MP 1,1-5,1 Mac Pro 3.1 Shut Down randomly

[Degtus]

Hi.
Not so long ago I bought a Mac Pro 3.1.
Found that he sometimes refuses to start if he stood off for more than an hour. In this case, it does not reach the sound of turning on and the Mac just turns off. The time from switching on to spontaneous switching off is different, but, as a rule, does not exceed a second. (I can record a video if required.)
It often happens that it starts normally, but turns off in the middle of the macOS boot (it happened on different versions and sometimes from Installation USB Stick). At the same time, it can remain on for a long time while waiting for a disk to be loaded. (If I press an Option/Alt key)
Sometimes it starts normally.
It happens that it turns off when the system is already loaded, without issuing any messages. Just a “click” - and I see a black screen. More often this happens immediately after login.

The problem is not due to HDD/SSD — Because I tried several different models from different manufacturers.
The CMOS-battery already changed.
Resetting NVRAM/PRAM does not help.
Turning off power supply for a long time does not help.

I give a configuration below.
CPU — 2 * Xeon X5482 3.2 GHz
RAM — 4 GB on 2 risers (Transcend 2G 2Rx8 DDR2 800 FB on each riser)
Graphics — AMD Radeon HD 5770 1 GB

 

[Degtus]

Today I tried to turn it on. Happened.
I was able to get a log, but found nothing useful.
Despite the fact that the last 3 shutdowns were sudden.

Spoiler: Shut down cause log

ProDegtus:~ degtus$ log show --predicate 'eventMessage contains "Previous shutdown cause"' --last 1000h Filtering the log data using "eventMessage CONTAINS "Previous shutdown cause"" Skipping info and debug messages, pass --info and/or --debug to include. Timestamp Thread Type Activity PID TTL 2020-06-12 10:24:17.785952+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-12 10:31:10.742541+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-12 10:33:34.752541+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-12 10:35:06.749354+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-12 10:37:18.743601+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-12 10:41:00.766468+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-12 11:54:34.781841+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-12 14:11:07.752879+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-12 21:43:25.745439+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-13 12:51:55.730814+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-13 12:55:18.791715+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-13 12:57:58.744777+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-13 13:10:29.779873+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-13 13:29:38.720463+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 2020-06-13 13:36:53.704937+0300 0xb4 Default 0x0 0 0 kernel: (AppleSMC) Previous shutdown cause: 0 -------------------------------------------------------------------------------------------------------------------- Log - Default: 15, Info: 0, Debug: 0, Error: 0, Fault: 0 Activity - Create: 0, Transition: 0, Actions: 0

I also got a full log in the last 5 minutes. 20 seconds after completion of this operation, the computer shuts down spontaneously.

12 MB 5 minutes full log file

I noticed that if I use a hairdryer to slightly heat the power supply, the computer turns on and works for a while.
All fans are operating normally.

Can someone provide a MacPro 3.1 power circuit diagram?