This part is a special connecting mechanism, it is located between the axle and the hub. A disk with a tire is attached to the latter. Such a part is made of two rings, and conical elements are inserted between them, insulated with a rubber part. This element is classified as rolling bearings. The wheel bearing resource is quite large and averages 150 thousand kilometers. The part can not be changed for 5 years.
How to understand that the wheel bearing is defective? In such a case, an unpleasant and very low-frequency rumble is added to the standard tire noise while driving. In addition to the constant hum while driving, a wheel bearing failure may be accompanied by the following “symptoms”:
- The car pulls to the side - this is due to the fact that the faulty part seems to stop. As a result, the car pulls to the right or to the left, as if there was a camber failure.
- With a worn bearing, vibration usually appears, while driving it gives off to the steering wheel and to the body. This is one of the clear signs of a bad wheel bearing. It is important to replace this element as soon as possible, as the clip is very worn out, and a “wedge” is about to occur.
Another of the signs of a rolling bearing failure is a kind of crunch when the car is moving. This happens due to the fact that the clip has almost completely collapsed and the spherical elements are located incorrectly. It is easy to recognize such a crunch, it is well audible in the cabin.
Why is a bad bearing dangerous?
If you ignore the hum that appears, which is characteristic of a wheel bearing failure, then it will intensify. As a result, it will be noticed not only by the driver, but also by all passengers. An unpleasant noise when a wheel bearing fails is not the main problem.
Much worse, if no action is taken, the element may jam. As a result, the axle shaft is completely deformed, and the ball joint of the lever instantly fails. It is especially dangerous when such a breakdown occurs when driving at high speed, for example, outside the city.
Why can a bearing fail?
Such elements have a long service life and break quite rarely. However, every motorist still faces a similar problem. The most common root cause of wheel bearing failure is driving on bad roads. The bad condition of the roads always entails serious consequences for the car. That is why the load on the entire suspension is significantly increased.
Another cause of failure is improperly pressed bearings.
If it does not stand correctly, for example, obliquely, then it will wear out pretty quickly. Enough of it no more than 2 - 3 thousand kilometers.
How to check for wheel bearing failure
The very first sign that the front wheel bearing is faulty will be a very low-frequency and very unpleasant rumble, which gradually only grows. And yet, how to check the front wheel bearing? For the most detailed definition, it is possible to adopt the following method, which uses left and right turns.
- When turning to the left, the car begins to roll to the right. In the same case, the greatest load will go to the right wheel, the entire load is removed from the left.
- When driving a car at a speed of 10 to 15 km per hour, due to a very sharp turn of the steering wheel to the left, the extraneous hum completely subsides. This means that there are problems with the wheel bearing of the left wheel. If the noise goes away when turning only to the right, then the right wheel bearing is broken.
To make the diagnosis most correct, you will need to raise the car with a jack or a lift (if any). After the engine of the car accelerates to 4 gears. The speed should reach 70 - 80 km per hour with the help of a car jack. It is required to start the engine, disperse the car, squeeze the clutch, and then disengage the gear. Next, you need to leave the cabin, and then accurately determine the source of the noise by ear. When the wheel is fully up, you need to take it in your hands along the upper and lower parts, starting to swing it in a vertical position.
The presence of even a small backlash - in this case, we can talk about the identified failure of the wheel bearing.
In exactly the same way, you can see the presence of play when the wheel is rocking also in a horizontal plane. There is another option how to check the wheel bearings:
- First you need to put the car on a flat surface. For this purpose, the most even asphalt surface will ideally go.
- First of all, a check is made for the backlash of the vertical axis. To do this, you need to take the wheel at the top point and try to swing it strongly.
- If clicks are heard, then we can already talk about the presence of hub play.
- To be completely sure that there is a bearing failure, you need to raise the wheel using a jack and begin to rotate it quickly by hand. If there is a crunch, it's time to go to the service station.
Drivers have long been accustomed to comfortable conditions in the cabin, which are provided by air conditioning. Therefore, its breakdown significantly affects the well-being of the driver and passengers. Repair and maintenance of car air conditioners is usually carried out by specialists at the service station, but in order to save money, the driver can do it with his own hands, having the necessary tools at hand. The article describes how to detect malfunctions of the car air conditioner and repair it yourself.
The air conditioner consists of several elements that form a closed system with a front and rear circuit, through which freon moves - coolant. The circulation in the rear and front refrigerant circuits is carried out by the compressor. The compressor compresses the freon, providing pressure in the system. In the compressor, the refrigerant is heated and exits as a gas. Freon enters the condenser, where the system cools the gas, and it turns into condensate.
Then the refrigerant is cleaned of impurities in the receiver-drier and moves to the thermostatic expansion valve (TRV). Next, the liquid refrigerant enters the radiator, where it again turns into a gaseous state. At the same time, it cools the air by absorbing heat from it. The radiator greatly cools the air as it passes through it. Cooled air enters the cabin. Freon returns to the compressor through the rear circuit, and the cycle repeats from the beginning.
Any of the elements of the air conditioning system can become unusable, which will affect the operation of the entire system. Therefore, you need to figure out what malfunctions can occur, how to diagnose them, why this or that malfunction occurred, and how to fix it.
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How to identify a malfunction?
To troubleshoot with your own hands, you do not need a tool, you should diagnose the system when it is working: visually inspect the rear and front circuits, listen to the noise and smells produced, check if water is dripping. If there are extraneous sounds and unpleasant odors, water is dripping - all this indicates some kind of malfunction.
If faults are found after diagnosis, they should be fixed immediately to avoid more expensive repairs.
Below are the types of faults and their causes:
We repair the compressor
If the compressor does not turn on, then this takes the air conditioning system out of service. The first cause of a malfunction may be a freon leak, therefore, first of all, it is necessary to diagnose the system to detect refrigerant leaks.
To do this, inspect the following structural elements:
- cracks on the air conditioner housing due to equipment defects;
- malfunction of the line tube, it can be frayed, especially for the air conditioning of rear seat passengers, since the pipeline passes under the bottom of the car;
- wear of rubber gaskets at the junctions of the elements of the system, the pump.
Particular attention should be paid to the gasket of the compressor. Compressor failure can be caused by faulty electronics and a clogged capacitor. Usually the compressor is not repaired, but replaced with a new element.
The exact cause of equipment failure can be given by a complete diagnosis using professional equipment.
Fix freon leak
If the car air conditioner turns on, but it does not cool the air in the cabin, then you need to find the reason why. The reason for this, most likely, is a freon leak on the front or rear circuit, at the joints. This is the most common air conditioner problem. This breakdown can be avoided if the machine is diagnosed and serviced on time.
Before fixing a refrigerant leak, you need to find the leaks. Diagnosis is performed without tools using special gas analyzers that detect the presence of freon and can pinpoint the exact location of the leak.
The second way: charging the system with refrigerant with an ultraviolet dye. Checking the front and rear circuits, as well as the entire system, is carried out using an ultraviolet lamp. If a leak is detected, you must either replace the part, or, if the part is metal, put a patch, having prepared the necessary tools and materials. Worn rubber parts should be replaced with new consumables.
We repair pipes and hoses
Any air conditioning system on a car includes pipes, rubber gaskets, seals, and line hoses. All of them are connected into a single system, with a front and rear circuit, ensuring its tightness. If one of the elements becomes unusable, then depressurization occurs, water drips and the air conditioner does not work well. After a visual inspection and detection of refrigerant leaks, it is necessary to replace the damaged parts, both the front and rear circuits, and refuel the system with freon.
Small cracks on aluminum tubes can be eliminated by hand without tools by processing with special compounds. With their help, soldering cracks in the form of patches is performed. Mixtures are applied to holes in several layers, the thickness of which is 2-3 mm. If the cracks are large - 2-3 mm wide, then the repair of auto-conditioners is carried out using argon-arc welding. You need to purchase a special tool: pipe bending machine, pipe cutter and welding. Instead of a pipe cutter, you can use a metal file.
In order for the details of the front and rear contours to remain elastic, it is necessary to constantly use the air conditioner for prevention, even in winter, and monitor its cleanliness.
We fix the radiator
The air conditioner radiator is located in such a place that it is constantly affected by various objects: dirt, pebbles, water, salts and more. Over time, it wears out, corrosive processes occur, and equipment depressurizes. This is manifested in the fact that the system does not cool the air, water begins to drip.
The best way out in this situation is to buy a new unit, since if you repair the capacitor with your own hands, there is a high probability that depressurization will occur elsewhere. Water will drip again and new repairs will be required. In addition, if special equipment, welding and tools are used to troubleshoot, the working lines are blocked, which affects the power and productivity of the air conditioner.
Summarizing
If the car has been operated for some time with a removed compressor or a faulty concessionaire, as well as after a do-it-yourself repair, before filling the air conditioning system, it needs to be flushed. During flushing, dirt, moisture, various contaminants, used oil, which interfere with the quality operation of the air conditioner, will be removed from the system.
Flushing of the equipment is also necessary when the compressor cycles, as in this case metal chips and other contaminants can get in. Do-it-yourself washing requires a lot of time and effort, as you have to wash each part separately. For do-it-yourself washing, you will need a tool for disassembling and assembling equipment and special tools with which all contaminants are easily removed.
Repair of car air conditioners is best done at a service station, since high pressure is involved in the air conditioning system. After repair work, it will be necessary to flush and refuel the system with freon and oil, while you need to know exactly the amount of liquid to be filled. The service station has all the necessary equipment, tools for repairing, washing and refueling the air conditioner.
Each car owner must monitor the condition of his car and, for the sake of prevention, regularly diagnose and maintain all car equipment.
Video "Car air conditioner maintenance"
This video from "Autodiagnostics 24" tells how to diagnose, repair and refuel a car air conditioner.
Regular automatic transmission diagnostics will help to avoid serious malfunctions and, in the event of the first signs of a breakdown, solve the problem at an early stage of its development.
Diagnosis of automatic transmission independently
What to look for before buying a car with automatic transmission?
Driving a car with an automatic transmission is very comfortable and convenient. But the cost of a new car with such a transmission is somewhat higher than the equivalent on the "mechanics". Therefore, often motorists turn to buying a used car. In this situation, you need to be very careful and know how to check automatic transmission before buying a car. Here are some tips to remember and stop buying if:
- previously a car with automatic transmission was under a taxi;
- the gearbox has already been repaired;
- the car was restored after the accident;
- the car has a towbar (towing contributes to the wear of the automatic transmission).
If you do not want to buy a pig in a poke, we recommend that you conduct a thorough automatic box computer diagnostics in a specialized car service.
Reasons for the breakdown of the automatic transmission
The failure of an automatic transmission can be caused by various reasons that can be combined into several related items:
Malfunction of the control cable due to incorrect adjustment or souring;
Breakdown of hydraulics or mechanical part of the system;
Wear of friction discs;
Or freewheels;
Malfunction of electronics (for example, control unit);
Violation of the general automatic transmission settings.
If the transmission began to function with deviations, there were suspicions of its breakdown, then urgent automatic box check. The sooner the cause is identified, the less expensive the repair will be.
Transmission diagnostics. How to check automatic transmission?
We tried to collect in one article all the diagnostic procedures that will help you figure out what exactly failed in the automatic transmission. We advise you to search for a breakdown of the “machine” in the following sequence:
- checking the level and condition of the oil;
- visual check of the throttle valve control cable;
- stall test check on a braked car;
- car diagnostics in motion;
- oil pressure check.
Checking the level and condition of the oil
Before proceeding with this procedure, let's take a closer look at . In fact, there is nothing difficult in this. We start the car engine and switchselector box to position "P" (parking). While the car is idling, check the oil. We take out the dipstick, wipe it and insert it back. After that, take out the dipstick again and look at what level the oil is. Now you need to wipe the probe with white paper. There should be no traces of metal shavings or other extraneous microelements on the paper sheet. If the oil has darkened (ideally it should be red), then it has not been changed for a long time. On some modern models of cars with automatic transmission, the indicated probe is missing. In such a situation, you can check the level and condition of the oil only in a car service.
Checking the level and condition of fluid in the automatic transmission | Video
Checking the adjusting cable
next step automatic transmission diagnostics is to check the throttle valve control cable or, as it is also called, the adjusting cable. During the operation of the gearbox, the adjusting cable wears out, which leads to disruption of the entire transmission. In particular, the need for cable adjustment is indicated by premature gear shifting at high or low speeds. As a result, the wear of the main components of the box increases, and fuel consumption also increases. The cable may need to be lubricated or tightened if it is loose.
How to check the automatic transmission on a stationary car
This procedure is recommended to be carried out in the presence of a qualified specialist. The so-called Stall Test is carried out on a fully braked car, with the engine running at maximum power. As a result of this test, it is possible to evaluate the braking properties of friction discs, the quality of the torque converter and the engine as a whole.
Before checking, you must make sure that the car is safely braked. Set the automatic transmission selector to the "P" position, and also apply the main and auxiliary brakes. In addition, fix the wheels with any stops. When carrying out the check, there should be no people in front and behind the car.
This test will not take long. For automatic transmission checks you need to do the following:
- switch the automatic transmission selector to the "D" mode;
- depress the throttle pedal as much as possible;
- fix the maximum engine speed;
- move the gearshift lever to "neutral" (position "N") and let the engine idle for at least one minute, this will cool it down.
If during this procedure unusual extraneous noises appear in the operation of the engine, then the check must be urgently stopped.
After that, it is necessary to compare the obtained indicators with the values set by the manufacturer. If the number of revolutions exceeds the manufacturer's figures, then the problem is probably low pressure in the main line. If, on the contrary, the number of revolutions does not reach the recommended value, then, most likely, the clutch of the free movement of the torque converter reactor has become unusable.
How to check the automatic transmission in the movement of the car
Road testing is one of the most important automatic transmission diagnostic tools. During this test, the following transmission performance indicators are checked:
Timeliness of gear shifting;
No jerks when driving;
The presence of third-party noise or vibration under the hood;
Correct operation of the box in various driving modes;
Timely response of the box, no slippage.
If, as a result of this check, slipping of the car or an unforeseen increase in engine speed when shifting gears was detected, then, most likely, the friction discs or a problem in the freewheel have become unusable.
Checking the oil pressure in the automatic transmission
Automatic transmission diagnostics completed by checking the oil pressure. This procedure must be carried out in strict accordance with the requirements of the vehicle operation manual. This is due to the fact that the process of this diagnosis is different for each.
After checking, it is necessary to compare the obtained indicators with the values \u200b\u200bspecified by the manufacturer. If there are deviations from the recommended indicators, then we can talk about the presence of malfunctions in the operation of the transmission hydraulic system. The definition of a problem area depends on the experience and knowledge of the basics of the operation of this automatic transmission model. If there is no such knowledge, then you should contact the professionals in a specialized service center.
In progress automatic transmission diagnostics Don't be in a hurry as you may miss important details. It is also necessary to pay attention to the little things, they will help to understand a possible problem in more detail. Self-diagnosis of the automatic transmission box does not cause great difficulties. Any novice driver can handle this. However, if you want to be completely confident in the automatic transmission, you need to contact the service station.
Pressure test - Video
Many PC owners are faced with various errors and failures in the computer, but cannot determine the cause of the problem. In this article, we will look at the main ways to diagnose a computer, allowing you to independently identify and fix various problems.
Keep in mind that high-quality computer diagnostics can take a whole day, allocate it in the morning specifically for this, and do not start everything in the late afternoon.
I warn you that I will write in detail as for beginners who have never disassembled a computer in order to warn about all the possible nuances that can lead to problems.
1. Disassembling and cleaning the computer
When disassembling and cleaning the computer, do not rush, do everything carefully so as not to damage anything. Store the accessories in a safe place prepared in advance.
It is not advisable to start diagnostics before cleaning, since you will not be able to identify the cause of the malfunction if it is caused by clogged contacts or the cooling system. Additionally, diagnostics may fail to complete due to repeated failures.
Unplug the system unit from the outlet at least 15 minutes before cleaning to allow the capacitors to discharge.
Perform disassembly in the following sequence:
- Disconnect all wires from the system unit.
- Remove both side covers.
- Disconnect the power connectors from the video card and remove it.
- Remove all memory sticks.
- Disconnect and remove the cables from all drives.
- Unscrew and remove all discs.
- Disconnect all power supply cables.
- Unscrew and remove the power supply.
There is no need to remove the motherboard, CPU cooler, case fans, you can also leave the DVD drive if it works fine.
Gently blow out the system unit and all components individually with a powerful stream of air from a vacuum cleaner without a dust bag.
Carefully remove the cover from the power supply and blow it through without touching the electrical components and the board with your hands and metal parts, as there may be voltage in the capacitors!
If your vacuum cleaner does not work for blowing out, but only for blowing in, then it will be a little more difficult. Clean it well so that it pulls as hard as possible. We recommend using a soft bristle brush when cleaning.
You can also use a soft brush to remove stubborn dust.
Thoroughly clean the CPU cooler heatsink, first considering where and how much dust it has clogged with dust, as this is one of the common causes of CPU overheating and PC crashes.
Also make sure that the cooler mount is not broken, the clamp is not open and the heatsink is firmly pressed against the processor.
Be careful when cleaning the fans, do not let them spin too much and do not bring the vacuum cleaner nozzle close if it is without a brush, so as not to beat off the blade.
At the end of cleaning, do not rush to collect everything back, but proceed to the next steps.
2. Checking the motherboard battery
The first thing after cleaning, so as not to forget later, I check the battery charge on the motherboard, and at the same time reset the BIOS. In order to pull it out, you need to press the latch with a flat screwdriver in the direction indicated in the photo and it will pop out by itself.
After that, you need to measure its voltage with a multimeter, optimally if it is in the range of 2.5-3 V. The initial voltage of the battery is 3 V.
If the battery voltage is below 2.5 V, then it is advisable to change it already. The voltage of 2 V is critically low and the PC is already starting to fail, which manifests itself in resetting the BIOS settings and stopping at the beginning of the PC boot, prompting you to press F1 or some other key to continue booting.
If you do not have a multimeter, you can take the battery with you to the store and ask them to check it or just buy a replacement battery in advance, it is standard and very inexpensive.
A clear sign of a dead battery is the constantly flying date and time on the computer.
The battery needs to be changed in a timely manner, but if you don’t have a replacement on hand now, then simply do not disconnect the system unit from the power supply until you change the battery. In this case, the settings should not fly off, but problems can still arise, so do not delay.
Checking the battery is a good time to completely reset the BIOS. This resets not only the BIOS settings, which can be done through the Setup menu, but also the so-called volatile CMOS memory, which stores the parameters of all devices (processor, memory, video card, etc.).
Errors inCMOSare often the cause of the following problems:
- computer does not turn on
- turns on once
- turns on and nothing happens
- turns on and off
I remind you that before resetting the BIOS, the system unit must be unplugged from the outlet, otherwise the CMOS will be powered by the PSU and nothing will work.
To reset the BIOS for 10 seconds, close the contacts in the battery connector with a screwdriver or other metal object, this is usually enough to discharge the capacitors and completely clear the CMOS.
A sign that the reset has occurred will be a lost date and time that will need to be set in the BIOS the next time the computer boots.
4. Visual inspection of components
Carefully inspect all capacitors on the motherboard for swelling and leakage, especially in the area of \u200b\u200bthe processor socket.
Sometimes capacitors do not bulge up, but down, which causes them to tilt as if they were just slightly bent or unevenly soldered.
If some capacitors are swollen, then you need to send the motherboard for repair as soon as possible and ask to re-solder all the capacitors, including those that are next to the swollen ones.
Also inspect the capacitors and other elements of the power supply, there should be no swelling, drips, signs of burning.
Inspect the disc contacts for oxidation.
They can be cleaned with an eraser and after that it is imperative to replace the cable or power adapter with which this disk was connected, since it is already damaged and oxidation has most likely occurred due to it.
In general, check all the cables and connectors so that they are clean, with shiny contacts, tightly connected to the drives and the motherboard. All cables that do not meet these requirements must be replaced.
Check that the wires from the front of the case to the motherboard are connected correctly.
It is important that the polarity is observed (plus to plus, minus to minus), since there is a total mass on the front panel and non-observance of the polarity will lead to a short circuit, due to which the computer may behave inappropriately (turn on every other time, turn itself off or reboot) .
Where the plus and minus in the contacts of the front panel is indicated on the board itself, in the paper manual for it and in the electronic version of the manual on the manufacturer's website. On the wire contacts from the front panel, it is also indicated where the plus and minus are. Usually the white wire is negative, and the positive connector can be indicated by a triangle on the plastic connector.
Many even experienced builders make a mistake here, so check.
5. Checking the power supply
If the computer did not turn on at all before cleaning, then do not rush to assemble it, the first thing to do is check the power supply. However, in any case, it won’t hurt to check the PSU, maybe it’s because of it that the computer fails.
Check the power supply when fully assembled to avoid electric shock, short circuit, or accidental fan failure.
To check the power supply, short the only green wire in the motherboard connector with any black one. This will signal to the PSU that it is connected to the motherboard, otherwise it will not turn on.
Then turn the power supply into the surge protector and press the button on it. Do not forget that the power supply itself may also have an on / off button.
A spinning fan should be a sign of turning on the power supply. If the fan does not spin, then it may have failed and needs to be replaced.
In some silent power supplies, the fan may not start spinning immediately, but only under load, this is normal and can be checked during PC operation.
Use a multimeter to measure the voltage between the pins in the connectors for peripheral devices.
They should be approximately in the following range.
- 12 V (yellow-black) - 11.7-12.5 V
- 5 V (red-black) - 4.7-5.3 V
- 3.3 V (orange-black) - 3.1-3.5 V
If any voltage is missing or goes far beyond the specified limits, then the power supply is faulty. It is best to replace it with a new one, but if the computer itself is inexpensive, then repairs are allowed, PSUs lend themselves to this easily and inexpensively.
The start of the power supply and normal voltages is a good sign, but in itself it does not mean that the power supply is good, since failures can occur due to voltage drops or ripple under load. But this is already determined in the subsequent stages of testing.
6. Checking the power contacts
Be sure to check all electrical contacts from the outlet to the system unit. The socket must be modern (for a European plug), reliable and not loose, with clean elastic contacts. The same requirements apply to the surge protector and cable from the computer power supply.
Contact must be reliable, plugs and connectors must not dangle, spark or be oxidized. Pay close attention to this, as poor contact is often the cause of failure of the system unit, monitor, and other peripheral devices.
If you have a suspicion of a power outlet, surge protector, power cable for a system unit or monitor, then change them as soon as possible to avoid damaging your computer. Do not delay and do not skimp on this, as repairing a PC or monitor will cost significantly more.
Also, poor contact is often the cause of PC failures, which are accompanied by a sudden shutdown or reboot, followed by failures on the hard drive and, as a result, disruption of the operating system.
More failures can occur due to voltage drops or ripples in the 220 V network, especially in the private sector and remote areas of the city. In this case, failures can occur even when the computer is idle. Try to measure the voltage at the outlet immediately after a spontaneous shutdown or reboot of the computer and observe the readings for a while. So you can identify long-term drawdowns, from which a linear-interactive UPS with a stabilizer will save.
7. Assembling and turning on the computer
After cleaning and inspecting the PC, carefully assemble it and carefully check that you have connected everything you need. If the computer refused to turn on before cleaning or turned on every other time, then it is advisable to connect the components in turn. If there were no such problems, then skip the next section.
7.1. Step by step PC build
First, connect the motherboard power connector and the processor power connector to the motherboard with the processor. Do not insert RAM, video card and do not connect disks.
Turn on the power of the PC and if everything is fine with the motherboard, the CPU cooler fan should spin. Also, if a buzzer is connected to the motherboard, a beep code usually sounds, indicating the lack of RAM.
Memory installation
Turn off the computer with a short or (if not possible) long press of the power button on the system unit and insert one stick of RAM into the colored slot closest to the processor. If all slots are the same color, then just the one closest to the processor.
Make sure that the memory bar is inserted evenly, all the way and the latches snap into place, otherwise it may be damaged when you turn on the PC.
If the computer starts up with one memory bar and there is a beep, then a code usually sounds, signaling that there is no video card (if there is no integrated graphics). If the beep code indicates problems with the RAM, then try inserting another bar in the same place. If the problem continues or if there is no other bar, then move the bar to another nearest slot. If there are no sounds, then everything is probably fine, continue on.
Turn off the computer and insert the second stick of memory into the slot of the same color. If the motherboard has 4 slots of the same color, then follow the instructions for the motherboard so that the memory is in the slots recommended for dual-channel mode. Then turn it on again and check if the PC turns on and what beeps it makes.
If you have 3 or 4 sticks of memory, then just insert them in turn, each time turning off and on the PC. If the computer does not start with a certain bar or gives a memory error code, then this bar is faulty. You can also check the motherboard slots by rearranging the work bar in different slots.
Some motherboards have a red indicator that glows in case of memory problems, and sometimes a segment indicator with an error code, the decoding of which is in the motherboard manual.
If the computer starts, then further memory testing occurs at another stage.
Installing a graphics card
It's time to test the video card by inserting it into the top PCI-E x16 slot (or AGP for older PCs). Do not forget to connect additional power to the video card with the appropriate connectors.
With a video card, the computer should start normally, without beeps, or with a single beep, indicating a normal self-test.
If the PC does not turn on or emits a beep error code for the video card, then it is most likely defective. But do not rush to conclusions, sometimes you just need to connect a monitor and keyboard.
Monitor connection
Turn off the PC and connect the monitor to the video card (or motherboard if there is no video card). Make sure that the connector to the video card and the monitor is connected tightly, sometimes tight connectors do not go all the way, which is the reason for the lack of image on the screen.
Turn on the monitor and make sure that the correct signal source is selected on it (the connector to which the PC is connected, if there are several).
Turn on the computer and a graphic splash screen and motherboard text messages should appear on the screen. Usually this is a suggestion to enter the BIOS using the F1 key, a message about the absence of a keyboard or boot devices, this is normal.
If the computer turns on silently, but there is nothing on the screen, there is most likely something wrong with the video card or monitor. The video card can only be checked by moving it to a working computer. The monitor can be connected to another working PC or device (laptop, player, tuner, etc.). Do not forget to select the desired signal source in the monitor settings.
Keyboard and mouse connection
If everything is fine with the video card and monitor, then we move on. In turn, connect the keyboard first, then the mouse, each time turning off and on the PC. If the computer freezes after connecting the keyboard or mouse, then they need to be replaced - it happens!
Connecting Drives
If the computer starts with a keyboard and mouse, then we begin to connect hard drives in turn. Connect a second drive without an operating system (if any) first.
Do not forget that in addition to connecting the interface cable to the motherboard, you also need to connect the connector from the power supply to the disk.
Then turn on the computer and if it comes to BIOS messages, then everything is fine. If the PC does not turn on, freezes or turns off by itself, then the controller of this disk is out of order and needs to be changed or taken in for repair to save data.
Turn off the computer and connect the DVD drive (if any) with an interface cable and power supply. If after that problems arise, then the drive fails in power supply and needs to be changed, it usually does not make sense to repair.
At the end, we connect the main system disk and prepare to enter the BIOS for initial setup before starting the operating system. We turn on the computer and if everything is fine, proceed to the next step.
When you turn on your computer for the first time, enter the BIOS. Usually, the Delete key is used for this, less often others (F1, F2, F10 or Esc), which is indicated in the prompts at the beginning of the download.
On the first tab, set the date and time, and on the “Boot” tab, select your hard drive with the operating system as the first boot device.
On older motherboards with a classic BIOS, it might look like this.
On more modern ones with a graphical shell, UEFI is a little different, but the meaning is the same.
To exit the BIOS and save the settings, press F10. Do not get distracted and watch the operating system fully boot to notice possible problems.
After the PC has finished booting, check if the fans of the processor cooler, power supply and video card are working, otherwise it makes no sense to carry out further testing.
Some modern video cards may not turn on the fans until a certain temperature of the video chip is reached.
If any of the case fans are not working, then this is not a problem, just plan to replace it in the near future, do not be distracted by it now.
8. Error analysis
Here, in fact, diagnostics begin, and all of the above was only preparation, after which many problems could go away and without it it made no sense to start testing.
8.1. Enabling memory dumps
If blue screens of death (BSOD) appear during computer operation, this can greatly facilitate the identification of a malfunction. A prerequisite for this is the presence of memory dumps (or at least self-written error codes).
To check or enable the dump recording function, press the key combination "Win + R" on the keyboard, enter "sysdm.cpl" in the line that appears and press OK or Enter.
In the window that appears, go to the "Advanced" tab and in the "Startup and Recovery" section, click the "Options" button.
The "Write debug information" field should be "Small memory dump".
If so, then you should already have previous error dumps in the C:\Windows\Minidump folder.
If this option was not enabled, then dumps were not saved, enable it at least now to be able to analyze errors if they are repeated.
Memory dumps may not be able to be created during severe crashes such as rebooting or shutting down the PC. Also, some system cleaning utilities and antiviruses can remove them, you must disable the system cleaning function for the duration of the diagnosis.
If there are dumps in the specified folder, then proceed to their analysis.
8.2. Memory dump analysis
To analyze memory dumps in order to identify what causes failures, there is a wonderful BlueScreenView utility, which you, along with other diagnostic utilities, can download in the "" section.
This utility shows the files that have failed. These files belong to the operating system, device drivers or some program. Accordingly, by the ownership of the file, you can determine which device or software was the cause of the failure.
If you cannot boot your computer in normal mode, then try booting into safe mode by holding down the "F8" key immediately after the disappearance of the motherboard graphic splash screen or BIOS text messages.
Go through the dumps and see which files appear most often as the culprits of the crash, they are highlighted in red. Right-click on one of these files and view its Properties.
In our case, it is easy to determine that the file belongs to the nVidia video card driver and most of the errors were caused by it.
In addition, in some dumps, the file "dxgkrnl.sys" appeared, even from the name of which it is clear that it refers to DirectX, which is directly related to 3D graphics. So, it is most likely that the video card is to blame for the failure, which should be subjected to thorough testing, which we will also consider.
In the same way, you can determine that the cause of the failure is a sound card, network card, hard drive, or some kind of program that gets deep into the system such as an antivirus. For example, if a disk fails, the controller driver will crash.
If you cannot determine which driver or program a particular file belongs to, then look for this information on the Internet by the name of the file.
If failures occur in the sound card driver, then most likely it is out of order. If it is integrated, then you can disable it through the BIOS and install another discrete one. The same can be said about the network card. However, network failures can be caused, which often resolves by updating the network card driver and connecting to the internet through a router.
In any case, do not make hasty conclusions until the diagnostics are completed, maybe your Windows just crashes or a virus has climbed, which is solved by reinstalling the system.
Also in the BlueScreenView utility, you can see the error codes and inscriptions that were on the blue screen. To do this, go to the "Options" menu and select the "Blue Screen in XP Style" view or press the "F8" key.
After that, switching between errors, you will see how they looked on the blue screen.
By the error code, you can also find a possible cause of the problem on the Internet, but it is easier and more reliable to do this by file ownership. You can use the F6 key to return to the previous view.
If different files and different error codes appear in errors all the time, then this is a sign of possible problems with RAM, in which everything crashes. We will diagnose it first of all.
9. Testing RAM
Even if you think that the problem is not in the RAM, still check it first. Sometimes a place has several problems, and if the RAM fails, then diagnosing everything else is quite difficult due to frequent PC failures.
Running a memory test from a boot disk is a must, as it is difficult to get accurate results on a Windows operating system on a failed PC.
In addition, "Hiren's BootCD" contains several alternative memory tests in case "Memtest 86+" does not start and many more useful utilities for testing hard drives, video memory, etc.
You can download the "Hiren's BootCD" image in the same place as everything else - in the "" section. If you do not know how to burn such an image to a CD or DVD, refer to the article where we reviewed, everything is done in the same way.
Set BIOS to boot from DVD drive or use Boot Menu as described in , boot from Hiren's BootCD and run Memtest 86+.
Testing can last from 30 to 60 minutes, depending on the speed and amount of RAM. One full pass should be completed and the test will go for the second round. If everything is fine with the memory, then after the first pass (Pass 1) there should be no errors (Errors 0).
After that, testing can be interrupted using the "Esc" key and the computer will restart.
If there were errors, then you will have to test each bar separately, taking out all the others to determine which one is broken.
If the broken bar is still under warranty, then take a photo from the screen using a camera or smartphone and present it to the warranty department of the store or service center (although in most cases this is not necessary).
In any case, it is not advisable to use a PC with a broken memory and carry out further diagnostics before replacing it, as various incomprehensible errors will pour in.
10. Preparation for component tests
Everything else, except for RAM, is tested from under Windows. Therefore, in order to exclude the influence of the operating system on the test results, it is advisable to do, if necessary, temporarily and most.
If this is difficult for you or there is no time, then you can try testing on the old system. But, if failures occur due to malfunctions in the operating system, some kind of driver, program, virus, antivirus (i.e., in the software part), then testing the hardware will not help determine this and you may go the wrong way. And on a clean system, you will have the opportunity to see how the computer behaves and completely eliminate the influence of the software component.
Personally, I always do everything right from start to finish as described in this article. Yes, it takes a whole day, but neglecting my advice, you can fight for weeks without determining the cause of the problem.
The fastest and easiest way is to test the processor, unless of course there are obvious signs that the problem is, say, in the video card, which we will discuss below.
If your computer, after some time after turning on, starts to slow down, freezes when watching videos, in games, suddenly reboots or turns off under load, then there is a possibility of overheating of the processor. In fact, this is one of the most common causes of such problems.
At the stage of cleaning and visual inspection, you should have made sure that the CPU cooler is not clogged with dust, its fan rotates, and the heatsink is firmly pressed against the processor. I also hope you didn't take it off when you cleaned it, as that requires replacing the thermal paste, which I'll talk about later.
We will use "CPU-Z" for the stress test with the processor warming up, and "HWiNFO" for monitoring its temperature. Although it is better to use the proprietary utility of the motherboard to monitor the temperature, it is more accurate. For example, ASUS has "PC Probe".
To begin with, it would be nice to know the maximum allowable thermal package of your processor (T CASE). For example, for my Core i7-6700K it is 64°C.
You can find out by going to the manufacturer's website from an Internet search. This is the critical temperature in the heat spreader (under the processor cover), the maximum allowed by the manufacturer. Don't confuse it with the temperature of the cores, which is usually higher and is also displayed in some utilities. Therefore, we will focus not on the temperature of the cores according to the processor sensors, but on the overall temperature of the processor according to the readings of the motherboard.
In practice, for most older processors, the critical temperature above which failures begin is 60 °C. The most modern processors can work at 70 ° C, which is also critical for them. You can find out the real stable temperature of your processor from tests on the Internet.
So, we launch both utilities - “CPU-Z” and “HWiNFO”, find the processor (CPU) temperature sensor in the motherboard indicators, run the test in “CPU-Z” with the “Stress CPU” button and monitor the temperature.
If after 10-15 minutes of the test the temperature is 2-3 degrees lower than the critical one for your processor, then there is nothing to worry about. But, if there were failures under high load, then it is better to run this test for 30-60 minutes. If during testing the PC freezes or reboots, then you should think about improving the cooling.
Keep in mind that a lot also depends on the temperature in the room, it is possible that in cooler conditions the problem will not manifest itself, but in hotter conditions it will immediately make itself felt. So you always need cooling with a margin.
In case of CPU overheating, check if your cooler complies with . If not, then you need to change it, no tricks will help here. If the cooler is powerful enough, but can't cope a little, then you should change the thermal paste for a more efficient one, and at the same time the cooler itself may be installed more successfully.
From inexpensive, but very good thermal pastes, I can recommend Artic MX-4.
It should be applied in a thin layer, after removing the old paste dry and then with cotton wool soaked in alcohol.
Replacing thermal paste will give you a gain of 3-5 ° C, if this is not enough, then simply install case fans, at least the most inexpensive ones.
14. Drive testing
This is the longest stage after the RAM test, so I prefer to leave it for last. To begin with, you can test the speed of all disks using the HDTune utility, to which I give "". This sometimes helps to identify freezes when accessing the disk, which indicates problems with it.
Look at the SMART options, where "disk health" is displayed, there should be no red lines and the overall status of the disk should be "OK".
You can download the list of the main SMART parameters and what they are responsible for in the "" section.
A full surface test can be performed using the same utilities from under Windows. The process can take 2-4 hours depending on the size and speed of the disk (about 1 hour for every 500 MB). At the end of the test, there should not be a single broken block, which are highlighted in red.
The presence of such a block is an unequivocal verdict for the disk and a 100% guarantee case. Save your data faster and change the drive, just don't tell the service that you dropped your laptop
You can check the surface of both conventional hard drives (HDD) and solid state drives (SSD). The latter really do not have any surface, but if the HDD or SSD drive freezes every time during the check, then the electronics most likely will fail - you need to change or repair (the latter is unlikely).
If you are unable to diagnose the disk from under Windows, the computer crashes or freezes, then try to do this using the MHDD utility from the Hiren's BootCD boot disk.
Problems with the controller (electronics) and the disk surface lead to windows with errors in the operating system, short-term and complete freezes of the computer. Usually these are messages about the impossibility to read a particular file and memory access errors.
Such errors can be mistaken for problems with the RAM, while the disk may well be to blame. Before you panic, try updating the disk controller driver, or vice versa, return the native Windows driver as described in.
15. Testing the optical drive
To check an optical drive, it is usually enough to simply burn a verification disc. For example, using the Astroburn program, it is in the "" section.
After burning a disc with a message about successful verification, try to completely copy its contents on another computer. If the disc is readable and the drive reads other discs (except for poorly readable ones), then everything is fine.
Drive problems I've encountered include electronic failures that completely hung up or prevented the computer from turning on, breakage of the retractable mechanism, contamination of the laser head lens, and breakage of the head as a result of improper cleaning. In most cases, everything is solved by replacing the drive, since they are inexpensive and even if they have not been used for several years, they die from dust.
16. Hull check
The case also sometimes breaks, then the button sticks, then the wiring from the front panel falls off, then it closes in the USB connector. All this can lead to unpredictable behavior of the PC and is solved by a thorough inspection, cleaning, tester, soldering iron and other improvised means.
The main thing is that nothing is short, which may be indicated by a broken light bulb or connector. If in doubt, disconnect all wires from the front of the case and try to work at the computer for a while.
17. Checking the motherboard
Often, checking the motherboard comes down to checking all the components. If all the components individually work fine and pass the tests, the operating system is reinstalled, but the computer still crashes, it may be the motherboard. And here I won’t help you, only an experienced electronics engineer can diagnose it and identify a problem with a chipset or processor socket.
The exception is the crash of a sound or network card, which is solved by disabling them in the BIOS and installing separate expansion cards. You can resolder the capacitors in the motherboard, but let's say replacing the north bridge, as a rule, is not advisable, since it is expensive and there are no guarantees, it is better to immediately buy a new motherboard.
18. If nothing helps
Of course, it's always better to find the problem yourself and determine the best way to solve it, as some unscrupulous repairmen strive to hang noodles on your ears and tear off three skins.
But it may be that you follow all the recommendations, but you will not be able to determine the problem, it happened to me. In this case, the matter is more often in the motherboard or in the power supply, maybe there is a microcrack in the textolite and it makes itself felt from time to time.
In this case, nothing can be done, bring the entire system unit to a more or less well-established computer company. No need to wear parts in parts, if you are not sure what the matter is, then the issue will never be resolved. Let them figure it out, especially if the computer is still under warranty.
Computer store specialists usually do not worry, they have a lot of different components, they just change something and see if the problem is gone, thus fixing the problem quickly and simply. They also have enough time to conduct tests.
19. Links
Transcend JetFlash 790 8GB
Hard drive Western Digital Caviar Blue WD10EZEX 1 TB
Transcend StoreJet 25A3 TS1TSJ25A3K
There are two test methods for diagnosing a malfunction in an electronic system, device, or printed circuit board: functional testing and in-circuit testing. Functional control checks the operation of the module under test, and in-circuit control consists in checking individual elements of this module in order to find out their ratings, polarity, etc. Usually, both of these methods are applied sequentially. With the development of automatic control equipment, it became possible to very quickly in-circuit control with an individual check of each element of the printed circuit board, including transistors, logic elements and counters. Functional control has also moved to a new qualitative level due to the use of computer data processing and computer control methods. As for the principles of troubleshooting themselves, they are exactly the same, regardless of whether the check is carried out manually or automatically.
Troubleshooting must be carried out in a certain logical sequence, the purpose of which is to find out the cause of the malfunction and then eliminate it. The number of operations performed should be kept to a minimum, avoiding unnecessary or meaningless checks. Before checking a faulty circuit, you need to carefully inspect it for possible detection of obvious defects: burned out elements, breaks in conductors on a printed circuit board, etc. This should be given no more than two to three minutes, with the acquisition of experience such visual control will be performed intuitively. If the inspection did not give anything, you can proceed to the troubleshooting procedure.
First of all, it is performed functional test: the operation of the board is checked and an attempt is made to determine the faulty block and the suspected faulty element. Before replacing a defective element, you must carry out in-circuit measurement parameters of this element in order to verify its malfunction.
Functional Tests
Functional tests can be divided into two classes, or series. Tests series 1, called dynamic tests, applied to a complete electronic device to isolate a faulty stage or block. When the specific block with which the fault is associated is found, tests are applied series 2, or static tests, to identify one or two possibly faulty elements (resistors, capacitors, etc.).
Dynamic tests
This is the first set of tests performed when troubleshooting an electronic device. Troubleshooting should be carried out in the direction from the output of the device to its input along bisection method. The essence of this method is as follows. First, the entire circuit of the device is divided into two sections: input and output. A signal is applied to the input of the output section, similar to the signal that, under normal conditions, acts at the split point. If at the same time a normal signal is obtained at the output, then the fault must be in the input section. This input section is divided into two subsections and the previous procedure is repeated. And so on, until the fault is localized in the smallest functionally distinct stage, for example, in the output stage, video amplifier or IF amplifier, frequency divider, decoder, or a separate logic element.
Example 1. Radio receiver (Fig. 38.1)
The most suitable first division of the radio receiver circuit is the division into the AF section and the IF / RF section. First, the AF section is checked: a signal with a frequency of 1 kHz is fed to its input (volume control) through an isolation capacitor (10-50 uF). A weak or distorted signal, as well as its complete absence, indicate a malfunction of the AF section. We now divide this section into two subsections: the output stage and the preamplifier. Each subsection is checked starting from the output. If the AF section is OK, then a clear tone signal (1 kHz) should be heard from the loudspeaker. In this case, the fault must be sought inside the IF / RF section.
Rice. 38.1.
You can very quickly verify the serviceability or malfunction of the AF section using the so-called "screwdriver" test. Touch the end of a screwdriver to the input terminals of the AF section (after setting the volume control to maximum volume). If this section is OK, the loudspeaker hum will be clearly audible.
If the fault is found to be within the IF/RF section, it should be divided into two subsections: the IF section and the RF section. First, the IF section is checked: an amplitude-modulated (AM) signal with a frequency of 470 kHz 1 is fed to its input, i.e., to the base of the transistor of the first IF, through a decoupling capacitor with a capacitance of 0.01-0.1 μF. FM receivers require a 10.7 MHz frequency modulated (FM) test signal. If the IF section is OK, a clean tone (400-600 Hz) will be heard through the loudspeaker. Otherwise, the IF partitioning procedure should be continued until the faulty stage, such as an IF or a detector, is found.
If the fault is within an RF section, then the section is split into two subsections, if possible, and checked as follows. An AM signal with a frequency of 1000 kHz is fed to the input of the cascade through a decoupling capacitor with a capacity of 0.01-0.1 μF. The receiver is tuned to receive a radio signal with a frequency of 1000 kHz, or a wavelength of 300 m in the medium wave band. In the case of an FM receiver, a test signal of a different frequency is naturally required.
You can also use an alternative verification method - method of cascading verification of the signal passage. The radio turns on and tunes in to a station. Then, starting from the output of the device, using an oscilloscope, the presence or absence of a signal at the control points is checked, as well as the compliance of its shape and amplitude with the required criteria for a working system. When troubleshooting in any other electronic device, a nominal signal is applied to the input of this device.
The considered principles of dynamic tests can be applied to any electronic device, provided that the system is properly partitioned and the parameters of the test signals are selected.
Example 2. Digital divider and display (Fig. 38.2)
As can be seen from the figure, the first test is performed at the point where the circuit is divided into approximately two equal parts. To change the logical state of the signal at the input of block 4, a pulse generator is used. The Light Emitting Diode (LED) at the output should change state if the latch, amplifier, and LED are OK. Further troubleshooting should be continued in the dividers preceding block 4. The same procedure is repeated using the pulse generator until the faulty divider is determined. If the LED does not change state in the first test, then the fault is in blocks 4, 5, or 6. Then the pulse generator signal should be applied to the input of the amplifier, etc.
Rice. 38.2.
Principles of static tests
This series of tests is used to determine the defective element in the cascade, the failure of which was established at the previous stage of checks.
1. Start by checking static modes. Use a voltmeter with a sensitivity of at least 20 kOhm/V.
2. Measure voltage only. If you want to determine the amount of current, calculate it by measuring the voltage drop across a resistor of known value.
3. If measurements at direct current did not reveal the cause of the malfunction, then and only then proceed to dynamic testing of the faulty stage.
Testing a single-stage amplifier (Fig. 38.3)
Typically, the nominal values of the DC voltages at the control points of the cascade are known. If not, they can always be estimated with acceptable accuracy. By comparing the actual measured voltages with their nominal values, you can find a defective element. First of all, the static mode of the transistor is determined. There are three options here.
1. The transistor is in a cutoff state, not producing any output signal, or in a state close to cutoff (“goes” into the cutoff region in dynamic mode).
2. The transistor is in saturation, producing a weak distorted output signal, or in a state close to saturation ("goes" into saturation in dynamic mode).
$11. Transistor in normal static mode.
Rice. 38.3. Rated voltages:
V e = 1.1 V, V b = 1.72 V, V c = 6.37V.
Rice. 38.4. Open resistor R 3, transistor
is in cutoff state: V e = 0.3V
V b = 0.94V V c = 0.3V.
After the real operating mode of the transistor is set, the reason for the cutoff or saturation is found out. If the transistor is operating in normal static mode, the fault is related to the passage of an AC signal (such a fault will be discussed later).
cutoffThe cut-off mode of the transistor, i.e., the cessation of current flow, occurs when a) the base-emitter junction of the transistor has zero bias voltage or b) the current flow path is broken, namely: when the resistor breaks (burns out) R 3 or resistor R 4 or when the transistor itself is faulty. Normally, when the transistor is in the cutoff state, the collector voltage is equal to the power supply voltage V CC . However, if the resistor breaks R 3 collector "floats" and theoretically should have the potential of the base. If you connect a voltmeter to measure the voltage across the collector, the base-collector junction is in forward bias conditions, as seen in Fig. 38.4. In the circuit "resistor R 1 - base-collector junction - voltmeter "current will flow, and the voltmeter will show a small amount of voltage. This reading is entirely related to the internal resistance of the voltmeter.
Likewise, when the cutoff is caused by an open resistor R 4, the emitter of the transistor "floats", which theoretically should have the base potential. If you connect a voltmeter to measure the voltage at the emitter, a current flow circuit is formed with a forward biased base-emitter junction. As a result, the voltmeter will show a voltage slightly higher than the nominal voltage at the emitter (Fig. 38.5).
In table. 38.1 summarizes the faults discussed above.
Rice. 38.5.Open resistorR 4, transistor
is in cutoff state:
V e = 1.25 V, V b = 1.74 V, V c = 10 V.
Rice. 38.6.Transition short circuit
base-emitter, the transistor is in
cut-off state:V e = 0.48 V, V b = 0.48 V, V c = 10 V.
Note that the term "high V BE " means the excess of the normal forward bias voltage of the emitter junction by 0.1 - 0.2 V.
Transistor failure also creates cutoff conditions. The voltages at the control points depend in this case on the nature of the fault and the ratings of the circuit elements. For example, a short circuit of the emitter junction (Fig. 38.6) leads to the current cutoff of the transistor and the parallel connection of resistors R 2 and R 4 . As a result, the potential of the base and emitter is reduced to a value determined by the voltage divider R 1 – R 2 || R 4 .
Table 38.1. Cutoff conditions
|
Malfunction |
Cause |
|
V b V c V BE |
vac |
Open resistor R 1 |
V b V c V BE |
High Normal V CC Low |
Open resistor R 4 |
V b V c V BE |
Low Low Low Normal |
Open resistor R 3 |
In this case, the collector potential is obviously equal toV CC . On fig. 38.7 considers the case of a short circuit between the collector and the emitter.
Other cases of transistor failure are given in Table. 38.2.
Rice. 38.7.Short circuit between collector and emitter, transistor is in cutoff state:V e = 2.29 V, V b = 1.77 V, V c = 2.29 V.
Table 38.2
|
Malfunction |
Cause |
|
V b V c V BE |
0 Normal V CC Very high, cannot be sustained by functioning pn-transition |
Breaking the base-emitter junction |
V b V c V BE |
Low Low V CC Normal |
Discontinuity of base-collector junction |
As explained in ch. 21, the transistor current is determined by the forward bias voltage of the base-emitter junction. A small increase in this voltage leads to a strong increase in the current of the transistor. When the current through the transistor reaches its maximum value, the transistor is said to be saturated (is in a state of saturation). Potential
Table 38.3
|
Malfunction |
Cause |
|
V b V c |
High ( V c) High Low |
Open resistor R 2 or low resistance resistorR 1 |
V b V c |
Low Very low |
Capacitor short circuitC 3 |
collector decreases with increasing current and when saturation is reached, it is practically equal to the emitter potential (0.1 - 0.5 V). In general, at saturation, the potentials of the emitter, base, and collector are approximately at the same level (see Table 38.3).
Normal static modeThe coincidence of the measured and nominal DC voltages and the absence or low level of the signal at the output of the amplifier indicate a malfunction associated with the passage of the AC signal, for example, an internal open in the coupling capacitor. Before replacing a suspected open capacitor, make sure it is faulty by connecting a serviceable capacitor of close rating in parallel with it. Break of the decoupling capacitor in the emitter circuit ( C 3 in the diagram in fig. 38.3) leads to a decrease in the signal level at the output of the amplifier, but the signal is reproduced without distortion. A large leak or short circuit in this capacitor will usually change the DC mode of the transistor. These changes depend on the static modes of the previous and subsequent stages.
When troubleshooting, keep the following in mind.
1. Do not make hasty conclusions based on comparing the measured and rated voltages at only one point. It is necessary to record the entire set of measured voltages (for example, at the emitter, base and collector of the transistor in the case of a transistor stage) and compare it with a set of corresponding nominal voltages.
2. With accurate measurements (for a voltmeter with a sensitivity of 20 kOhm / V, an accuracy of 0.01 V is achievable), two identical readings at different control points in the vast majority of cases indicate a short circuit between these points. However, there are exceptions, so you need to perform all further checks for the final conclusion.
Features of diagnostics of digital circuits
In digital devices, the most common malfunction is the so-called “sticking”, when a logic 0 (“constant zero”) or logic 1 (“constant one”) level is constantly on the output of the IC or in a circuit node. Other failures are also possible, including breaks in the IC leads or a short circuit between the PCB traces.
Rice. 38.8.
Diagnostics of faults in digital circuits is carried out by applying the signals of a logical pulse generator to the inputs of the element under test and observing the effect of these signals on the state of the outputs using a logical probe. For a complete check of a logical element, its entire truth table is “passed”. Consider, for example, the digital circuit in Fig. 38.8. First, the logical states of the inputs and outputs of each logic element are recorded and compared with the states in the truth table. A suspicious logic element is tested using a pulse generator and a logic probe. Consider, for example, the logical element G 1 . At its input 2, the logic level 0 is constantly active. To check the element, the generator probe is installed at pin 3 (one of the two inputs of the element), and the probe probe is at pin 1 (element output). Referring to the truth table of the OR NOT element, we see that if one of the inputs (pin 2) of this element has a logical level of 0, then the signal level at its output changes when the logical state of the second input (pin 3) changes.
Element truth tableG 1
|
Conclusion 2 |
Conclusion 3 |
Conclusion 1 |
For example, if in the initial state a logical 0 is active at pin 3, then a logical 1 is present at the output of the element (pin 1). If now using the generator to change the logical state of pin 3 to logical 1, then the output signal level will change from 1 to 0, which and register the probe. The opposite result is observed when, in the initial state, a logic level of 1 acts on pin 3. Similar tests can be applied to other logic elements. In these tests, it is imperative to use the truth table of the logical element being tested, because only in this case can one be sure of the correctness of testing.
Features of diagnostics of microprocessor systems
Troubleshooting in a microprocessor system with a bus structure takes the form of sampling the sequence of addresses and data that appear on the address bus and data bus, and then comparing them to a well-known sequence for a running system. For example, a fault such as a hard 0 on line 3 (D 3 ) of the data bus would be indicated by a hard logical zero on line D 3 . The corresponding listing, called status listing, obtained using a logic analyzer. A typical status listing displayed on the monitor screen is shown in fig. 38.9. Alternatively, a signature analyzer can be used to collect a bit stream, called a signature, at some node in the circuit and compare it to a reference signature. The difference in these signatures indicates a malfunction.
Rice. 38.9.
This video talks about a computer tester for diagnosing problems with personal computers such as IBM PC:
