PlayStation Development Network

Hi,

I'm trying to repair a PSU from a SCPH-7502 unit and I'm looking for some helpful advice.

The PSU has this design:


The problem is that the console randomly resets at various points during gameplay. I've confirmed (by testing with spares) that the problem is with the PSU and not the mainboard or the laser unit. I've also confirmed the issue is specifically related to the reset rail (pin 5) on the PSU output connector. I did this by disconnecting pin5 and running the machine for several hours without problems.

From the diagram, it seems to me the reset rail is controlled by the component M51957B, which seems to be a voltage detector / reset IC . According to the datasheet this IC sends a time-delayed voltage to the output pin (5) when the input pin (2) goes above 1.25V.

I noticed, while testing, that the reset switch seems to default to the CLOSED position, unlike the diagram which says it should be OPEN. Is this normal? It means there's always 1.25V on the IC input pin and there's always a voltage on the output pin. Pressing the reset button temporarily opens the switch and then closes it again on release, causing the desired reset behaviour. It's not a big deal, I suppose, but I found it weird that the design differs from the spec.

As far as I can tell, the random reset problem could be any of the following:
1. The reset IC is broken.
2. The delay capacitor is broken.
3. The voltage on the input rail has a ripple causing it to sometimes dip below the 1.25V threshold (I measured it at ~1.3V ~1.5V).
4. Something else (???)

I disconnected the delay capacitor and tested it with my multimeter. It seems to be healthy. I also disconnected and tested all the other electrolytic capacitors on the board. They all appear healthy too and within tolerances. Tonight I'll try swapping out the reset IC with a spare from a useless 110V spare PSU.

I have no idea how to test for voltage ripples or if this reset issue is indicative of something more sinister.

Any advice?

Well, I swapped out the reset IC and left the machine running for some hours. No dice

I still have no idea how to test for ripples without an oscilloscope. I'm considering replacing the reset switch with a new one that's open by default to avoid the issue altogether.

Check the resistors and diodes around the reset switch too.

There's a good chance of cracked solder joint with these supplies. I would look for that on the low voltage side, due to the symptoms. But redo the 2 power socket connections anyway. Those always crack.

Then you'll have to weigh the risk and effort for fixing one of these very common supplies

Just watch that large filter capacitor when working on it. I've had them give me a good shock through my hand because I thought it was discharged.