Biostar A320MH Ver 6x - Turning off on random seconds/minutes

[xZeroCool]

Hi, I've got a Biostar A320MH Ver 6x. This motherboard basically turns off by itself even if I'm only in the BIOS Screen.
Sometimes it will just turn on but no display, but if it POSTed it will show CMOS Fail everytime.
The things I did to try fixing the problems with no luck.
1. Changing CMOS Battery
2. Reflash BIOS CHIP with latest bios file using desoldering method.
3. Check voltages and it is just normal.
Any ideas what the problem might be?

[xZeroCool]

I have now tried using brand new BIOS chip but it still the same problem

[xZeroCool]

I tried, reheating PCH and CPU VTT Controller, same problem.

[xZeroCool]

When I only insert the 24 PIN ATX without the 4 PIN CPU it will not shut off by itself after turning on.
Maybe a Mosfet Issue?

[DynaxSC]

Would guess some cold solder point or a cap on the edge of failing (random but recovering shorts). Quite difficult to trace. Could try to use freezing spray or heating areas to trace. Try bending the board to confirm/rule out a mechanical issue - bad solder point. Can also be the chipset partially defect or end of life, issue with RAM or maybe PSU, bad contacting of RAM modules or CPU. Mosfet issue - very unprobable, they usually work or fail completely (short), parts which can fail to some extent are any kind of caps, resistors (especially low ohm smd resistors 0 up to 50 ohms under relatively high load, they often increase the resistance under long time high load) and highly advanced VLSI chips, eg. chipsets, memories. Electrolytic caps' life span is dependent on working conditions (mainly working temperature) 10-15 years, after such time they might loose the capacity almost completely (dry out) and can lead to non-stability of power supply lines. BTW, reflow of PCH must not necesarilly repair a bad contact, only reballing is a 100% failsafe metod.

The variety of possible failures is very difficult to describe and assess. To give an example, I recently had a ITX board starting only sometimes after Power Button pressed. The issue was a non-visible part of a bad track inside the board layers which did not conduct the Power On signal all the time (probably a bad inter-layer via). With bending the board the conduction sometimes came back, then disappeared again. Addind a simple wire by-pass track solved the issue, the board was almost factory new. I would never imagine this is even possible, nor it would be possible to trace such a hidden issue. But a simple tracing of signal flow without much thinking discovered the issue.

[DynaxSC]

Just another fresh experience from today. Gigabyte Z690 Aorus Elite DDR4 - symptoms very similar to yours: board starts only randomly correctly (however started always, but usually no boot, CPU LED lit and not progressing), once started shuts down randomly within seconds to minutes. Starting again only randomly again. Board is ca. 1 year old.
The reason was very strange, a partially broken linear regulator (AP7365-WG-7) supposed to supply a fixed 3.3V VCC voltage for the main PWM controller RAA229131 (CPU VRM controller). Sometime it delivered the 3,3V as desired, but randomly the voltage dropped to 2,84V during operation - very, very strange and unbelievable bahavior.
I came on this as the VCORE was not always present when board started, staying on CPU LED. Measuring the RAA controller VCC showed the strange jumping supply voltage.
After replacing the regulator all symptoms went away, and the board boots and works stable.
Just an example, as your board is completely different in design, but it shows what funny things can happen 😁.