Console Repair

Hello,

so my old PS4 (Gen 1, I think, not a huge console person, it's my Bloodborne machine and nothing else) has an issue: it turns off after about 5 minutes of it being on, and when it reboots, it goes to safe mode, does some scans, boots and it happens again within 5 minutes.

At first I thought it was a heating issue or the old HDD breaking down, so I cleaned it thoroughly and replaced HDD with a new SSD. Issue did not go away, so in the name of troubleshooting, I blew cold air into it while it was on, but the exact same thing happened again. Have also reinstalled the OS clean when I swapped to the SSD, didn't do any cloning shenanigans.

Currently my theory is either the main board or PSU that's broken. One other idea I had was that the thermal compound has gone bad on CPU/GPU, but haven't tried replacing that yet, it seemed unlikely to be the issue after I increased the cooling temporarily, should have at least seen an increase in the time it stayed on by my logic.

I have another PS4 I found for free on second hand market app, seller said the PSU broke and is missing, but main board should work fine.

I've been googling this every once in a while, but haven't found any clear answers. I also took some measurements from the connectors, and they seem to give correct voltages, but haven't checked current, and haven't done any long term measurement when it shuts down, so no clue if it's a voltage spike or undervoltage that causes this issue. My oscilloscope is also out of commision, so that complicates any long term measurements.

Does this kind of issue ring a bell for everyone? Any further troubleshooting tips? Should I just plug the PSU into the other PS4 without a PSU and see if the same thing happens? Doesn't 100% rule out the mainboard being the issue, since I have no idea if the mainboard is a known good component on the spare part one either...

I'd really like to finish my Bloodborne perfectionist run some day :)