PS2 PSU no 12V

[rtstorm]

Hello, I have a PS2 fat console that has no 12V on the power supply board.

Thinks that I checked:

• Input
• Fuse
• 4 rectifier diode
• all small diodes on board
• replace the 2 green caps

I have 340V on the transformer's input but 0V on the outside (the DC side).
I have checked the optocoupler and I have 1.3V on the hot side and 0V on the DC side. I remove the octo from the board and it is ok

Board look's pretty simple but cannot figure it out

[stj]

replace the small cap near the heatsink - it starts the psu.

[rtstorm]

Woow that was fast, thank you it works now.

[CapLeaker]

You can also read this. https://www.badcaps.net/forum/showthread.php?t=43028

[Pharaoh35]

Sorry to high jack this thread, but being that it is already solved I am hoping to ask a few questions.

First question is for OP, rtstorm. Are you able to show what you did exactly? Is there a type of heat sink on the PSU that I am not familiar with, or are you referring to the heatsink on the main mobo?

Second question is for anybody that is willing to answer:
This PSU doesn't look like it is terribly complicated, so I was hoping for a general explanation on this circuits design. How does this PSU work?

I can see that that power is coming from the two prong connector. The fuse immediately after it, but then there are two black components with wound copper which I am not familiar with. I would assume the big cap there because it needs to regulate a large amount of voltage from the power source. I also know that the four pin connector is what powers the mobo. Everything seems like a mystery.

[CapLeaker]

Stj meant the little caps around the heat sink on the PSU.
Every power supply has a high voltage (hot or primary side) and a low voltage (cold or secondary) side. Each side has its own ground reference. So do not mix them up, it will screw your measurements.
Using that picture above, basically AC power comes in goes trough the fuse, then AC filtering inductors and a high voltage X cap, more filtering, bridge rectifier (4 diodes), an inrush current limiting resistor, the big fat high voltage bulk capacitor that holds the rectified AC voltage (120VAC x 1.414= 169.68VDC). Then this high DC voltage is getting switched on and off very fast using a mosfet and a gate drive circuit (this gate drive has a start up capacitor) and a feedback loop. The feedback loop is a voltage that’s comes from the secondary going through optoisolator and back into the gate drive. This is how the gate drive knows how hard it has to work. Back to the secondary. This high voltage, switched voltage (remember Mosfet) is going through the transformer. After that there is a rectifier diode, cap, inductor (filter), cap, the beginning of the feedback loop going to the hot side and the output. This is a very simple power supply, and they can get way more complicated than this.