PU22 board works fine from cold boot, won't restart after use.

[Ichisuke]

I have a PAL SCPH 7502 model with this strange issue.
Basically you can turn on the console and play just fine for hours.
Once you turned it off and instantly turn it on again, the console won't boot at all.
Just a black screen and nothing works (no disc spinning, moving laser etc).
If I wait like a couple of minutes, the console turn on again and works fine.
Also it doesn't do that if instead I reset the console while is still working, the reset doesn't cause the issue.

I know for sure it's not related to the PSU, since I even used a repsx psu, and the console has the same issue.
If it's a capacitor issue I don't know which one is to blame.
If it's a cold solder joint I really don't know where to look at...

[nocash]

What happens if you push the reset button while it hangs with black screen?

That's just the plain console, without any expansion carts attached?

Oh, and instantly switching it back on sounds like bad practice, I would wait 1-2 seconds betswen power cycles (just in case you literally meant "instantly").

[Ichisuke]

What happens if you push the reset button while it hangs with black screen?

That's just the plain console, without any expansion carts attached?

Oh, and instantly switching it back on sounds like bad practice, I would wait 1-2 seconds betswen power cycles (just in case you literally meant "instantly").

1) nothing, just stays on the black screen. I have yet to test if the console will "unfreeze" by leaving it like that and press reset at a later time.
Update: leaving the console.on the black screen and resetting, ot keeping the reset button down for about 1 minute won't unfreeze the console.

2)it does that with nothing attached to the console too (in fact I tested it even by simply tuning it on with a game)

3)I've found it by chance, changing a game disc. So instantly is the tests I've made. But in "normal use" think of the time you take for changing a game by power cycling the console instead of resetting it. I still have to check precisely how much time is needed before the console can boot again, but it can take several seconds. (Last test It took 25 seconds to boot again after about 40 minutes of playing)

I can leave the console on the black screen for some seconds, turn it off and then it turn on normally...
I also noticed (and this doesn't always happen) that when the screen is black with the console "turned on" the TV constantly flash the RGB signal "warning".

[nocash]

I would search for broken solder points. Visually inspect the through-hole solder points on the PCB bottom side. And for SMD chips, try to push down the CPU, Main RAM, BIOS ROM chips, and check if things get better (or worse) when booting up while pushing down those chips. As far as I remember, the boot screen should come up without CDROM drive connected, so you can put the CDROM drive aside when doing those tests.