Short or not? If yes, how to determine the culprit?

Question

Iron

Continuation of the story from this question:
How to properly clean a PC from a vape?
(hello, Hedgehog and V. Proskurin)
One computer was repaired by replacing the mother (diagnosis and replacement took place in the repair service). Well, plus a thoughtful self-cleaning after returning the computer home. Night killed. The computer worked, but artifacts appeared almost immediately. I uprooted the video card and took it back to the service, where it is still being diagnosed. I'm still working on the integration, the flight is normal.
I asked to clean the second computer already in the service (no moral strength left). And he resurrected without additional replacements, and BEFORE cleaning. I brought it home, it was useful to install a wireless mouse in the front USB connectors (ie, on the face of the Zalman Z9 U3 tower). There are 4 of them. I inserted it into the first connector - the monitor went out. In the second - it went out again. Etc. On the fourth connector, the computer was cut down again - the coolers were spinning, but there was no picture.
Brought it back. Replaced mom. Brought home. In the repair, they turned off the front connectors and advised not to use them. OK. Useful, then, to install a wireless mouse ...))) You probably already guess.
In general, I put the mouse receiver in the rear connector (that is, in the mother) - the cursor slows down. I thought that the signal is bad (although this mouse breaks through the walls and moves the cursor in another room). I connected a simple usb extension cable, which, by the way, came with [another] wireless mouse. The monitor is off. The extension cable, apparently, already managed to burn out from this - it does not work on any computer.
The image was restored after a couple of seconds. Looking ahead - the braked cursor was cured by new firewood, but at that time I did not know this. Plugged in a wired mouse. The same picture. Okay, I think I'll do it. Carefully pushed the computer - from the movement it was instantly knocked out, that is, everything inside is spinning, but there is no picture. This time at all.
Rebooted. Works. But now it's scary to use it. What to do? What advice?

Answer 1

As I understand it, we are talking about a stationary computer in the ZALMAN Z9 U3 case.
In general, a strange position for repairmen. "I took it back, they replaced the mother, they advised me."
They were not supposed to advise, but to test. Total. Generally. Front panel, mat. boards, power supply, fans. I suspect mat. the board could be replaced with a cheaper and lower quality one. The service is clearly not telling something or it is not known what it is doing.
The service had to say exactly which component, and how exactly, does not work.
By the way, they could replace anything at all. Once such an attitude.
It could be at least that way.
1. pull out the mat from the system unit. board, power supply, hdd. collect it all on a non-conductive table. turn on. see, touch, move.
2. low-quality mat. the board, especially from manufacturers such as acer, msi, lenovo, and others, can give big glitches as a result of the loss of contact either at the junction of the microcircuits with the board, or in the board itself. (poor-quality circuitry). (in fact, almost all motherboards from Chinese manufacturers (lenovo, ...) (and not assembled in China) can completely die at any moment, and drag along all hard drives, memory, processor, and everything in general ... ) (the contact may disappear from an attempt to move the board / connector. Or a new contact may appear).
3. if the stand assembled on the table is buggy, the problem may be in it. there, according to the circumstances - or we are looking for a normal mat. board, or we connect another power supply, and we understand that this power supply interferes, and therefore everything is cut down, etc. seagate hard drives, lenovo memory - they can give almost any effect at the slightest mechanical impact. (yes, hdd can drag the motherboard into reboot, and possibly freeze; from lenovo / huawei components, the motherboard can burn out along with everything).
4. why in the previous paragraph "possibly"? because the problem somehow came there. for example, from the body.
4.1 fans. may interfere with nutrition. result - failure on the mat. board or power supply for voltage regulation and / or voltage conversion circuits, as a result - freezes / glitches. (but it's probably different).
4.2 there may be an electrical contact on the reverse side of the mat. housing boards. for example, if there is something crumpled in the case, or if the brass pins with threads on which the mat is attached. fees are too short. (you can just put a new A4 sheet between the board and the back wall - then see if there are scratches on it. If there is, then there is contact, bad. New food plastic bags are also good for this).
4.3 A common problem is various expansion cards. or during installation with a metal plate (where the mount) of the card, you can pick something off the board, or this metal thing itself creates contact with the mat. board where it shouldn't be. especially true for, for example, tp-link network cards, which have a curved metal mount, or metal. fastening with burrs, can shorten the entire mat. fee.
5. a possible problem is the power supply. due to many reasons, up to static electricity along the 3.3 volt line, it can give various glitches to all power circuits. (due, for example, to malfunctions of the circuit that monitors the quality of the output voltage in the power supply. However, there may be other problems). can also respond to mechanical influences.
6. in fact, against static electricity and the mat itself. the board may fail. especially true for lenovo, it can burn the processor and memory from a freely hanging piece of twisted pair plugged into a network connector. (or if there are lenovo / huawei components, such as memory, especially early ones).
7. Let's assume that we figured out the motherboard, power supply, and hdd. what else is in the box? Front Panel. it can be unscrewed (if nothing is glued), connected to the mat. board, and check if you are not afraid to burn the mat. fee. can be checked with a device - you need two multimeters, wires, and a computer power supply. (check mainly for short circuit, and for current when voltage is connected (if there are any circuits)). you can connect another mat. board / old computer, and see how it works. (In general, USB circuits should be easier than ever ...). Now in the photo on the network I saw a temperature indicator on the case. after our services, or after the computer is assembled by a store / service, this thing may well start to fail. (could break and "repair").
8. in general, one of the testing methods at home, and when there is no equipment, we pull everything out from everywhere, lay it out on the table. works good? We are looking for a problem in what is not connected now. does it work badly? we replace the components sequentially with live ones (well, yes, we need another live computer), we look at whether it works or not. (if you are not afraid to burn good components). as an option - we put components on a live computer from a half-dead one, sequentially, until problems appear. as they appeared - the problem component was found.
9. In general, in fact, huawei / lenovo components should be a red light for you right away. they can quite, including, burn good components to which they are connected. (for example, huawei / lenovo memory may well spoil the motherboard and hdd - an empirical effect).
10. You wrote about the disappearance of the image. Are your monitor/monitor connectors/wire/monitor wires OK?
In general, good luck with your testing! In general, learn to do everything yourself. Good services are almost non-existent. Unfavorable for them. They work on the verge of cost, sometimes even used components. And they still pay rent and wages.