H370M-HDV/M.2 + TX750 V2 issue

PSU won't POST on one board, works fine on every other system

This has been driving me nuts for 3 days now. I have got 4 power supplies and my main PC only refuses to boot with one of them, and even that's not consistent, it randomly works sometimes. Let me just explain it in order of how it happened.

My main PC is an ASRock H370M-HDV/M.2 with an i5-9500 and 64GB RAM.

The PSUs I have got are:

- Corsair VS550 (non-modular)

- Corsair TX750 V2 (non-modular)

- Cooler Master Elite 500 (non-modular)

- MSI MAG A1000G (modular).

The VS550, the Cooler Master, and the MSI one all boot the board perfectly every single time, no issues at all. Its only the TX750 V2 that's causing problems.

When I plug the TX750 into this board and hit power, everything just turns on instantly, like normal. CPU fan spins, case fans spin, GPU fan and lights come on, HDD spins up. Its not shutting off or restart-looping or anything, it just stays on. But there is no display, no POST, and USB straight up doesn't work either, my mouse doesn't even light up. I plugged a USB drive in just to check and it's light blinked on for a second and then turned off.

I tried basically everything I could think of. Cleared CMOS, pulled the GPU and ran off the iGPU instead, dropped down to a single 8GB RAM stick, reseated the RAM, reseated the 24 pin and the 8 pin CPU connector like around 10 times, turned off Fast Boot, poked around with Deep Sleep settings (had to boot with the VS550 to get into BIOS for these), and BIOS is already the newest version. None of it made any difference at all.

At that point I was pretty sure the TX750 itself was just dying, so I went and tested it elsewhere. First I put it into an old H61 board with a Pentium, which only has a 4 pin CPU connector (TX750 has a 4+4 EPS connecter), so I tested each half of the connector separately just to be safe. Both halves booted that PC fine on their own.

Then just to be thorough I plugged the TX750 back into the H370 board again, and somehow it booted up, no GPU, single stick RAM. I actually thought maybe whatever was wrong had fixed itself. So I shut it down and turned it back on to double check, and nope, straight back to the same broken state, no post, no display, just fans spinning. Tried for a good 30 min after that to get it to boot again and had no luck.

So then I put the TX750 in a way more serious system to really push it. MSI H270 PC Mate with an i7-7700K and dual RTX 3060s. Booted totally fine on that one too. I even did a CPU stress-test and ran llama.cpp benchmark on both 3060s for like 30 minutes straight on it just to stress it, completely stable the whole time, no crashes or shutdowns or anything weird.

So by this point I know the TX750 boots an old basic system fine, it boots a modern demanding system fine even under real load, and my H370 board boots fine with 3 other totally different PSUs. Its literally just this one PSU with this one board that has a problem.

And here's the part that's really messing with my head. I moved the TX750 back onto the H370 board at night and left it, then next morning tried powering it on and it booted straight into Windows, no problem. I thought okay, maybe its actually fixed now. Did a restart after that and it worked too. But a restart is not really a full power cycle, so I shut it down and turned it back on, and immediately back to the same issue. Fans spinning, no display, no post.

After that I just left it alone and checked on it every couple hours for like 12 hours, no change at all. Also tried fully draining it, held the power button for 30 seconds with the PSU switched off and unplugged from the wall, then waited an hour before trying again. Same result.

Now its day 3 and I turned it on this morning and it actually booted. Still no GPU plugged right now, and based on how is been going, it will probably go right back to not posting the second I shut it down.

At this point I dont think the board is the problem since it works fine with 3 other PSUs, and I dont think the TX750 is faulty either since it runs two completely different systems no problem, one of them under real load for half an hour. Its just this specific pairing that breaks, and even then its not consistent, it randomly decides to boot sometimes.

Thanks to anyone who reads through this whole thing. Any input at all would help a lot.

Thanks for the reply. Your explaination is plausible. I have two questions.

One - I tested this TX750 V2 in an old H61 + Pentium system, and it booted perfectly. I also tested it in another system with an MSI H270 PC Mate, an i7-7700K, and dual RTX 3060s. It booted normally there as well, and I stress-tested the CPU while running a llama.cpp benchmark on both GPUs for about 30 minutes. It stayed completely stable with no crashes or shutdowns.

Assuming the PSU is starting to fail due to aging capacitors, would you still consider it safe to keep using it in the H270 system for the time being since it appears to work flawlessly there? I can plan to replace it in the near future. Or is there a risk it could silently damage the motherboard, CPU, GPUs, drives, or corrupt data even though the system appears completely stable?

Second, do you think this points more towards an aging PSU, or could this simply be a rare PSU-motherboard compatibility issue? I came across this Linus Tech Tips thread where the exact PSU model was RMA'd, yet the replacement showed the same behavior with one motherboard while working fine in another system, so the issue appeared to be compatibility rather than a faulty PSU. I'm wondering if my case could be something similar, or if the intermittent nature of my issue makes you lean more towards PSU aging instead.

https://linustechtips.com/topic/1150127-power-supply-working-in-one-system-but-not-another/