A device for repairing and testing computers - POST Card

Each time you turn on the power of an IBM PC (or compatible) and before it starts operating system The computer's processor performs a BIOS routine called Power On Self Test (POST). The same procedure is also performed by pressing the RESET button or the Ctrl-Alt-Del key combination. The main purpose of the POST procedure is to test the basic functions and subsystems of the computer (such as memory, processor, motherboard, video controller, keyboard, flexible and hard drives etc.) before loading the operating system. This insures the user to some extent from trying to work on a faulty system, which could lead, for example, to the destruction of user data on the HDD. However, a new specification for PC 2001 computers is currently being developed, which provides for a reduction in the time interval from the moment the PC is turned on to the start of the disk loader to 7 seconds (in the presence of SCSI devices - up to 10 seconds), including by reducing the POST procedure, which, in general, it should not please computer assemblers / repairers, and thoughtful users, too, I think: it’s better to lose 2 minutes than to restore the contents of the HDD later or wonder why the computer began to freeze so often. In the meantime, computers continue to delight professional computer builders/repairers with their built-in POST procedure, so let's look at the possibilities it provides for computer repair.

Before starting each of the tests, the POST procedure generates a so-called POST code, which is output to a specific address in the address space of the computer's input / output devices. If a fault is detected in the device under test, the POST procedure simply "freezes", and the previously displayed POST code uniquely determines which of the tests "freezes" occurred. Thus, the depth and accuracy of diagnostics with POST help codes are completely determined by the depth and accuracy of the tests of the corresponding BIOS POST procedure "a computer.

The port addresses for outputting POST codes depend on the type of computer: ISA, EISA - 80h, ISA-Compaq - 84h, ISA-PS / 2 - 90h, MCA-PS / 2 - 680h, some EISA - 300h, but in most cases (you can say, standard) port 80h is used. Since the POST procedure appeared in the IBM PC / XT with an eight-bit ISA system bus, it historically happened that POST codes are just one byte, which is listed in the POST code tables as one-digit hexadecimal numbers in the range 00h-FFh (0- 255 in decimal notation). It should be noted that the tables of POST codes are different for various manufacturers The BIOS and, due to the emergence of new tested devices and chipsets, are somewhat different even for different versions of the same BIOS manufacturer. POST code tables can be found on the respective websites of BIOS manufacturers: for AMI it is http://www.ami.com, for AWARD it is http://www.award.com, sometimes POST code tables are given in motherboard manuals (for example, manuals for P6SBA-P6DBS Supermicro boards).

To display POST codes in a human-friendly form, devices called POST Cards are used. POST Card is a common computer expansion card that is inserted (when the power is off!) into any free (corresponding to its slot - ISA or PCI) slot and has two seven-segment indicators for displaying POST codes. Previously, before the advent of the PC 99 and PC 99A specifications, the POST Card for the ISA bus was the most common. Now, due to the threat of the complete elimination of the ISA bus, more expensive POST Cards have begun to appear for PCI bus. For laptops that do not have ISA and PCI buses at all, POST Cards are available for installation in an LPT port. It should be noted that for the operation of such a POST Card, appropriate support is required from the BIOS "a laptop.

The simplest POST Card for the ISA bus from vendor noname displays POST codes at the fixed address 80h and has no switches to change this address. The passage of the RESET signal of the computer to such a POST Card is fixed by the blinking of the dots of the seven-segment POST code indicator or is displayed on it with special characters. More expensive POST Cards have switches for selecting the POST code port address, as well as additional LED indicators for the RESET and CLK signals of the system bus and indicators for the presence of supply voltages +5V (+3.3V), -5V, +12V, -12V. Such POST Cards are produced, for example, by Ultra-X, Inc (http://www.uxd.com) for ISA - QuickPOST PC and PCI - QuickPOST PCI buses, respectively. The same company also offers a POST Card for connecting to the LPT connector of laptops - MICRO POST. The original POST-Probe PCI from Micro2000, Inc (http://www.micro2000.com) is very interesting. On two adjacent sides of the PCI and ISA bus connectors are located at an angle of 90 degrees. It also includes an additional adapter for connecting to our exotic MicroChannel bus. Another POST Card manufacturer is DataDepot Inc (http://www.datadepo.com), which produces both the simplest POST Card (MiniPOST) and the more complex PocketPOST. However, the PHD 16 for the ISA (Professional Hardware Diagnostics) bus from Ultra-X, Inc. can be called a real professional tool. PHD 16 has two modes of operation: diagnostics and POST codes, which are selected by setting the appropriate jumpers. In the POST code mode, the codes generated by the POST system are simply displayed on a two-digit seven-segment PHD 16 indicator. The diagnostic mode is divided into a training mode - a long run of tests to detect floating errors motherboard BIOS boards are replaced with ROM BIOS Ultra-X with a special set of in-depth tests. As new motherboard chipsets are released, updated Ultra-X BIOS ROMs are also released. PHD 16 test results are displayed in special code on a seven-segment display and additional LEDs, and with a working video adapter, on a computer monitor. The more modern PHD PCI from Ultra-X, Inc. is designed for the PCI bus and, unlike the PHD 16, does not need an external video adapter, as it has a built-in standard SVGA video output for displaying test results on a monitor.

To better understand how to use the POST Card, consider a typical sequence of tests performed by the POST procedure:

1. Processor testing.
2. Checksum ROM BIOS.
3. Verification and initialization of the DMA, IRQ and 8254 timer controllers. After this stage, audio diagnostics become available.
4. Checking memory regeneration operations.
5. Testing the first 64 kB of memory.
6. Video controller initialization. After this step, diagnostic messages are displayed on the screen.
7. Testing the full amount of RAM.
8. Keyboard testing.
9. Testing CMOS memory.
10. Initialization of COM and LPT ports.
11. Initialization and test of the FDD controller.
12. Initialization and test of the HDD controller.
13. Search for additional ROM BIOS modules and initialize them.
14. Calling the operating system loader (INT 19h, Bootstrap), if the operating system cannot be loaded, an attempt to start ROM BASIC (INT 18h); on failure, system halt (HALT).

Before testing a computer using a POST Card, it is necessary to determine the BIOS manufacturer of the motherboard: this can be done either by the sticker on the BIOS chip, or by the inscriptions that are displayed on the screen by a similar working motherboard. Then you should find the appropriate POST code table for this BIOS: AMI - http://www.ami.com, AWARD - http://www.award.com.

The sequence of actions when repairing a computer using the POST Card is as follows:

1. Turn off the power of the faulty computer.
2. Install the POST Card in any free slot on the motherboard.
3. We turn on the power of the computer and read the corresponding POST code from the POST Card indicator, on which the computer boot "hangs".
4. Using the tables of POST codes, we determine which of the tests had problems and comprehend the probable causes.
5. When the power is off, we rearrange jumpers, cables, memory modules and other components in order to eliminate malfunctions.
6. We repeat points 3,4,5, achieving a stable passage of the POST procedure and the start of loading the operating system.
7. With the help of software utilities, we perform the final testing of hardware components, and in the case of floating errors, we carry out a long run of the corresponding software tests.

When repairing a computer without using the POST Card, points 2-4 of this sequence are simply omitted and from the outside, computer repair looks just like a feverish rearrangement of jumpers, memory, processor, expansion cards, power supply, and, to top it all, the motherboard. If large firms have a large stock of serviceable components, then for small firms and individuals, repairing a computer by installing known-good components becomes a difficult problem. It is even harder for service engineers who quickly travel to the customer and are forced to take a whole suitcase of spare parts with them. It happens that the replacement of computer components under the bewildered questions of the client stretches for whole hours and does not always lead to the desired result - you have to pick up the system unit or go for a new portion of serviceable parts.

How, in practice, is a computer repaired using a POST Card?

First of all, when the power is turned on, before starting the POST procedure, the system must be reset by the RESET signal, which is indicated on the POST Card by special characters or an LED. If the computer malfunctions in the most difficult case, the reset either does not work at all, or it does, but no POST codes are displayed on the indicator. In this case, it is recommended to immediately turn off the computer and remove all additional boards and cables, as well as memory from the motherboard, leaving only the motherboard itself with the processor and POST Card installed connected to the power supply.

If the next time you turn on the computer, the system resets normally and the first POST codes appear, then, obviously, the problem lies in the temporarily removed computer components; it is also possible, in incorrectly connected cables (especially often the IDE cable is inserted "upside down"). By inserting sequentially the memory, video adapter, and then other cards, and observing the POST codes on the indicator, a faulty module is detected. In case of faulty memory for computers with AMI BIOS, the sequence of POST codes usually stops at code d4 (for older 386/486 boards - at code 13); with AWARD BIOS - on codes C1 or C6. It happens that it is not the memory itself that is faulty, but, for example, the motherboard - the reason is poor contact in the SIMM / DIMM connectors (contacts are bent / closed to each other), or the memory itself is not fully inserted in the connector.

In case of a faulty video adapter for computers with AMI BIOS, the sequence of POST codes stops at codes 2C, 40 or 2A, depending on the BIOS modification, or skips these codes without the corresponding video card initialization lines appearing on the monitor (indicating the type, amount of memory and the manufacturer of the video adapter) .

Similarly, for computers with AWARD BIOS, if the video adapter fails, the POST code sequence either stops at code 0d, or skips this code (this is especially common on new Pentium I / Pentium II motherboards).

If the initialization of the memory and video adapter went well, then by installing the remaining cards one at a time and connecting the cables, based on the readings of the POST Card indicator, it is determined which of the components sits on the system bus and prevents the computer from booting.

Let us now return to the case when the initial reset of the system does not even pass (on the POST Card indicator at the very beginning of the test do not appear Special symbols, indicating the passage of the RESET signal or the corresponding LED does not light up). In this case, either the computer's power supply is faulty (for example, the PWRGOOD signal is not generated), or the motherboard itself (the RESET signal generation circuits are faulty).

The exact cause can be determined by connecting to motherboard a known good power supply.

Let us now consider the case when the reset signal passes, but no subsequent POST codes are displayed on the indicator; in this case, as described earlier, a system is tested, consisting only of the motherboard, processor, POST Card and power supply. If the motherboard is brand new, then the reason is usually in incorrectly set jumpers for selecting the frequency / multiplication / type of processor, sometimes in an incorrectly set Clear / Normal CMOS jumper. Very often, the reason for the failure is not pressing the processor to the stop in Slot 1 or the inverted position of the 486th processor. At the same time, if power is supplied to the motherboard with an incorrectly inserted processor for longer than 1-2 seconds, a complete failure of both the processor and the motherboard is possible.

From practice, it can be argued that the use of the POST Card, along with a good reaction of the engineer and fast shutdown power supply has already saved the life of more than one processor and motherboard.

If all jumpers and the processor are set correctly, but the motherboard still does not start, you should replace the processor with a known good one. If this does not help, then we can conclude that the motherboard or its components are malfunctioning (for example, the cause of the malfunction may be damage to information in the FLASH BIOS).

In conclusion, I would like to note that the main advantage of the POST Card is that it does not require a monitor for its operation, and testing a computer using the POST Card is possible at the early stages of the POST procedure, when sound diagnostics are not yet available, and even at the stage of sound diagnostics POST codes are much easier to understand than counting the duration and number of beeps on the computer. It can be said that the POST Card is the eyes and ears of a computer repair engineer.

Who can use the POST Card? First of all, service engineers, computer assemblers, salespeople in a computer store, system administrators - anyone who has to solve computer problems in a short time. The POST Card is also indispensable for professional motherboard repairers who make full use of the diagnostic capabilities of the POST BIOS procedure. Even convinced skeptics, after solving problems once or twice with the help of the POST Card, could no longer part with it, clutching at it in difficult cases, like a drowning man clutching at a straw. And, finally, the non-traditional use of POST Card by programmers who are very far from hardware problems is known. Since the status of the POST code port is displayed on the POST Card indicator, programmers, when debugging additional BIOS modules or programs of an industrial stand-alone control computer without a monitor, are able to track the passage of control points of your program by the POST Card indicator, simply by entering the conditional codes into the POST code register. For example, when programming in Turbo Pascal, in order to display the number 5Ah on the indicator of a POST Card operating at address 80h, you can use the statement:

port[$80]:=$5A;

And, finally, anticipating questions about where you can buy a POST Card? Industrial POST Card manufacturers classify computer repair equipment as professional, so if you have $100-150 (and for PHD PCI the price goes up to $1000), you can order a POST Card on the websites of the above manufacturers. The second way out is self-assembly of the simplest POST Card for the ISA bus. This POST Card with 8 LED binary code error indicator contains 4 widely available K555 (74LS) series ICs and can be made even by a novice radio amateur in 1-2 evenings, and the manufacturing cost is minimal.

The ISA bus is still quite popular, especially considering the fact that the simplest POST Card proposed for manufacturing will serve to repair a large number of already existing computers with the ISA bus. It is worth paying attention to the fact that many of the latest motherboards with the I820 chipset have one ISA slot. Therefore, I think that the simplest POST Card for the ISA bus will find application for at least another 2-3 years. In addition, the implementation of a POST Card for the PCI bus is quite complicated, since it requires special high-speed FPGAs and a specially manufactured printed circuit board, and is not available to a novice radio amateur.

A diagram of the simplest POST Card is shown in Figure 2, there is also a drawing of an expansion board with the numbering of the pins of the ISA connector to facilitate installation. On the DD2, DD3, DD4 chips, an output device address decoder is made with a fixed address 080h, which is most often used for issuing POST codes. The POST code values ​​coming from the SD0-SD7 data bus are fixed in the eight-bit register DD1 and displayed in binary form by the HL0-HL7 LEDs.

Any circuit board that has at least the first part of the ISA connector (pins A1-A31, B1-B31) is suitable for making a POST Card. As a last resort, you can use a cut-off from an old faulty MIO or VGA adapter lower part with an ISA connector by attaching a small piece of circuit board to it with two M3 screws. All connections on the circuit board are made with a thin stranded MGTF wire after the installation of discrete elements. In the design, you can use DD1 microcircuits of the K555IR23, DD2-K555LA2, DD3.4 - K555LE1 type, as well as their analogues from the K1533, K1531, K531 series (foreign 74LS, 74ALS, 74HC, 74F). LEDs HL0-HL7 must be placed in one row in the following order (from left to right):

HL7 HL6 HL5 HL4 HL3 HL2 HL1 HL0

These LEDs will display the POST code in binary form: the lit LED corresponds to a logical 1, the extinguished LED corresponds to 0. To translate the resulting binary code into two-digit hexadecimal form, accepted in the tables of POST codes, it is necessary to mentally divide the HL7 ... HL0 LEDs into two halves: the older one (HL7, HL6, HL5, HL4) and the younger one (HL3, HL2, HL1, HL0), then, according to table 1, determine for each half has its own hexadecimal character and mentally combine these characters in the correct order: the high half corresponds to the high character, and the youngest half to the low one. With some training, this whole procedure can be done in the mind.

After assembling the POST Card, you need to test it. To do this, you can use any program that allows you to enter arbitrary values ​​\u200b\u200bin the range 00h-FFh into the output device at address 080h, while you need to make sure that the POST Card indicator readings correspond to the data output to port 080h. Such a program can be obtained here: posttest.zip (4 Kb), in addition, it can be used for learning and training when translating POST codes from binary to hexadecimal.

What improvements can be proposed for the simplest POST Card? First of all, it is desirable to add the DD5 register (K555TM2) with the HL8 LED to fix the passage of the RESET signal (diagram in Figure 3). The RESET signal is generated by the computer's power supply when it is turned on, or when the RESET button is pressed. In the event of a complete failure of the motherboard with the installed processor, it may turn out that no POST codes are generated by this system, and the simplest POST Card (Figure 2) in this case will display random garbage that will be entered into the DD1 register every time the power is turned on. This garbage can be misinterpreted as some kind of POST code. If you install an additional register DD5 (Figure 3), then when a RESET signal is received and before the first POST code is written to the IC DD1, all LEDs HL0-HL1 POST codes will be extinguished by a high level at pin 1 of DD1. In addition, by a short flash of the HL8 LED, it will be possible to judge the passage of the RESET signal.

As a second improvement, we can propose the introduction of a decoder - a binary to seven-segment converter for displaying POST codes on a conventional two-digit seven-segment indicator. Unfortunately, I am not aware of standard one-two-bit microcircuits for converting a full four-bit binary code to seven-segment, but they can be replaced, for example, with programmable ICs. Schemes of the simplest seven-segment decoders, along with firmware for K155PE3, were published in the Radio magazine (for example, Radio N 12 for 1987, page 55). With some redundancy as a decoder, you can also use more affordable IS UFRZU K573RF2 (6). However, even the simplest POST Card displaying POST codes in binary form on 8 LEDs will significantly reduce the time for troubleshooting and, I hope, make life much easier for many computer assemblers/repairers!

Good day% habrauser%!

Most recently, I wrote a post about POST cards, good tautology a ;-)?
In it, I promised to write a sequel if the topic is interesting, and since the topic really turned out to be interesting to the Khabrovites, I continue!

Actually subject

As I mentioned in the comments, for my first article, I ordered cards for myself - this one for laptops and this one for desktops.

The order was placed on the twentieth of January (I can’t specify the exact dates, it was not me who ordered, tracked and received). The other day this card came, they say, a laptop one, you have to wait for a desktop one. Here I want to express some indignation -
1) The cards were ordered in one order, they go in different ways (I hope that the second one still goes, and is not lost);
2) Delivery times! Of course I can understand, they had Chinese New Year, but a month on the go (judging by the date on the package) is too much, especially in conjunction with the fact that they were completed with three ( THREE) weeks!
3) Diextreme takes about 200 rubles for issuing a parcel track, the track itself is free and is assigned to each parcel, so the verdict is hucksters!
On these points my indignation ends and I begin the review.

The card came in a parcel, inside the parcel is glued with a peace of mind generator, the card itself is packed in it and in anti-static, so the Chinese approach the packaging issues thoroughly. In anti static we have the card itself, USB cable and User Manual.

This card is designed for mini PCI and also has ( not intended why we read further) port for LPT, USB is needed to power the card. The first thing I wanted to do was naturally test it! But I don't have a laptop at hand, so with pure thoughts I decided to test it on the LPT port.

Actually stuck a card

When power is applied, the card displays "--" and "FF".

Turn on the car

Then the card changes the image several times, and again “FF00” the system boots up. A reasonable question and a desire to find out what kind of codes flashed, makes us make a simple conclusion that the only two buttons allow you to scroll through the codes, and voila! So it is, we poke on the button, we see

Now on the left scoreboard serial number POST code, on the right is the code itself. (not in order because it repeats at the beginning)

Tyk button

Tyk button

Tyk button

Poke again

Again poke

Once again

And a little more

Here is the last one

Here we come to one interesting point and not the most impressive conclusion.
An interesting point is the User manual, at the very beginning of the manual we have the designation of LEDs

"+5 volts" glows all the time while the mother is turned on, it is quite logical because USB ;-)

"+3.3 volts" the same power indicator as "+5 volts" does not light when there is no power to PCI slot(either the mother does not support, the couple did not figure out the exact translation, in the original )

"FRAME" lights up when the "FRAME" signal is active.

FRAME (I/O)
Contact A34

The FRAME signal is issued by the active master on the PCI bus. FRAME transition to low, i.e. active, the layer initiates the addressing phase. To signify the last data phase that completes the bus cycle, the main subscriber must deactivate FRAME again.

"CLK" lights up when the "CLK" signal is active.

CLK(O)
Contact B16

This pin carries the PCI timer signal that accompanies all PCI operations. In accordance with the technical requirements, its frequency lies in the range from 0 to 33 MHz.

"RSET" glows during reboot

"+12" turn on formal logic

"-12" enable formal logic

"-5" is the same as "+3.3 volts"

Decryption codes

BIOS on Phoenix mother.

FF in my cases is the presence of +5 on USB

A5 is not listed in the manual (just empty)

AA waiting for pressing F2

55 enable USB devices

04 get CPU type

The photos show "+5 volts"

So “an interesting point, the manual contains a table with all the codes for the Phinks, AMI Avardavian BIOSes, “not the most impressive conclusion” is that the card drives complete nonsense on LPT!

Speaking of the manual - 28 A6 pages of the purest information on POST codes, speaker signal designations and CMOS operation. I'll take care of the translations in the near future, and present it to the habrosociety, but I think I'll wait for the desktop map to make a consolidated manual.

I'm waiting for the second card and a martyr laptop for full-fledged tests and reviews. I translate and smoke the manual.

P.S Sunday at six o'clock in the morning, maybe I missed something. Questions in the comments, I will add if necessary.

P.P.S the article was written in real-time mode, “on the fly” while writing, rebooted and took a photo.

Two quotes were used in the preparation of the article

Testing faulty motherboards, whether desktop PCs or laptops, is unthinkable without POST cards. Unfortunately, in this moment the mini PCI bus in laptops is already gone, and there are no honest POST cards that work directly with the PCIe bus yet. All well-known testers, in fact, use the LPC bus, which some manufacturers output to the free pins of the mni PCIe connector. If the LPC bus is not brought out there, repairmen have to solder to some microcircuits on the board using enough a large number wires. No, of course, there are not very many of them, but I would still like it to be even less. Is it possible? It turns out that in many cases - yes!

Mysterious Connector

Let's take a look at the photo of the first laptop motherboard that came across. To do this, the author opened his own (the article is written on New Year's holidays, so the evil watchmen are not allowed to work).

Let's take a closer look at the connector marked with an arrow.

What's this? Unfortunately, the circuit of this particular board was not found in the collection (a shoemaker without boots), but here is a fragment of the circuit from a similar motherboard:

Turns out it's nothing more than a two-wire POST! And it is available on many motherboards manufactured by COMPAL (which are found in laptops from many manufacturers). True, on some, it is hidden under a sticker, but finding it is not so difficult, if there is a desire.

The abbreviation "P80" in the name of the chains means nothing more than "PORT 80", that is, the classic POST port.

Conclusion

Based on this, the ability to receive codes not only from traditional mini PCI and LPC buses, but also from this two-wire bus was added to the new POST testers of BVG Group. At the same time, the tester itself is still installed in the mini PCIe connector, from where it receives power (without this, the bus would be four-wire, you would also have to extend the ground and + 3.3V), and two additional wires are connected to a similar connector. After turning on the power, the tester detects the presence of a two-wire bus and starts diagnostics on it. Otherwise, the operation is completely identical to the classic modes of operation with the POST tester, you just need to solder less. In addition, it is necessary to solder not to the contacts of microcircuits with a small pitch, but to the seat for the connector, where the pitch is much larger. True, it is impossible to say that "this connector is standardized", there are also alternative pinouts, for example, the one below, but still, there are only two variants, and an error will not lead to any fatal consequences. It is enough to change the wires, and everything will work.

Greetings, dear Khabrovites!

Not the first year I have been engaged in diagnostics and resuscitation of desktops and laptops, mainly at the client's home. Over time, the conclusion suggests itself that it is necessary to have a suitcase with you, and perhaps even a suitcase with accessories for diagnosing a faulty piece of iron. Some may object to me - “You can do without components! Experience allows you to perform diagnostics without them! This is partly true, but it does not give one hundred percent accuracy, this is a fact.

Rely on speaker's POST codes? Not always possible specifically determine what he is complaining about. For example, one long, two short speaker beeps indicate a video system malfunction, but this does not always mean a malfunction of the video card itself. There are, for example, problems with additional power supply to this very video card, and this is already a malfunction of the power supply.

Here I will stop and tell dear readers what the speaker's signals are.

When you turn on the computer, the BIOS (basic input / output system) starts up - a fact known to everyone, but it will not be superfluous to mention. As part of the BIOS, there is a program called POST (power on self testing). As the name implies, the program is designed for initial diagnostics of devices and ports on the motherboard.

The POST initialization procedure is accompanied by displaying the image on the monitor:

After passing the POST, we see:

During POST execution, a so-called POST code is generated, which is written to a special diagnostic register.

Actually, the speaker signals are error codes when performing POST, if POST is performed without errors, we hear one short signal.

We pass to a subject.

POST cards.

POST card is an expansion card, most often there are PCI format cards:

There are also miniPCI cards (for laptops):

And there are cards for LPT (require additional USB power):

Having on hand a desktop with a wonderful diagnosis “does not turn on” (not to be confused with “does not start”), most often non-critical peripherals are first turned off sequentially - sound, tuner, network card, hard drives, drives.
Then, if no malfunctions are detected in the process, the replacement of components begins: RAM, video card, processor (yeah, the same suitcase with pieces of iron).

But here we have a POST card in our hands instead of a suitcase with iron, we save time bypassing the above procedure with replacing / turning off the iron (we save an average of 40 minutes, I note that after turning off one piece of iron, at least one on-off cycle is performed).

Actually, we insert our wonderful map and watch what happens.
And the following happens - on the scoreboard of the card we have post codes that indicate to us what is being tested in this moment. Having reached the faulty element, the POST execution procedure stops and the code remains on the scoreboard, most often a manual with POST codes is attached to the subject (they vary depending on the manufacturer and BIOS version).

By comparing the error code with its decoding, most often we get the final diagnosis, such as: faulty memory, processor, or a component on the motherboard.

I suppose to write a series of articles on diagnostics, if the topic is of interest to Khabrovites.