Mac Pro 3,1 w/ Weird OT Problems! Help!

[okyproxd]

Hi all, just picked up a Mac Pro 3,1 (Early 2008) for $25 on Facebook Marketplace. Seller claimed it was working and provided a photo of the About This Mac screen, but no video of it actually booting.

Symptoms:
- Press power button, fans whir up for about a second, relay click sound from PSU area, then shuts off immediately
- No chime, no video output
- OT_A and OT_B LEDs are lit red automatically (no DIAG button needed)
- When pressing DIAG button, only STBY lights up (yellow)
- RAM Boards light their DIMM LEDs for a second

What I've already tried:
- SMC reset (both button on logic board and unplugging for 15+ seconds)
- Reseated both RAM risers and all DIMMs
- Reseated GPU (ATI card, in slot 1)
- Removed PRAM battery entirely — no change
- Blasted interior with compressed air

GPU note: the PCIe retention latch broke during removal so the card is sitting without the latch, held in by the bracket screw only — not sure if this is relevant.

Are the CPU heatsink temperature sensors glitching out or something?

Is this a PSU issue, logic board, or CPU fault? Any help appreciated — I know OT_A/OT_B threads tend to be inconclusive so hoping someone has cracked this one.

 

[okyproxd]

Yes, this was made by AI lol

 

[bmoraski]

relay click sound from PSU area, then shuts off immediately


Are the CPU heatsink temperature sensors glitching out or something?

Is this a PSU issue, logic board, or CPU fault? Any help appreciated — I know OT_A/OT_B threads tend to be inconclusive so hoping someone has cracked this one.

If fans are cranking high i know that can be because of thermal paste being bad but not sure if it would shut down immediately. My guess would be power supply but hopefully someone else can chime in. Just my 2 cents

 

[okyproxd]

If fans are cranking high i know that can be because of thermal paste being bad but not sure if it would shut down immediately. My guess would be power supply but hopefully someone else can chime in. Just my 2 cents

I don't even think the fans start. The GPU fan starts for a sec alongside like every other moving part inside of the computer, but then shuts back off. I ordered a new PSU on eBay for $45 so I'll see what happens if I replace it. Really hoping that its not a logic board failure!