Buttons and lamps not working

[ersk3]

I had the issue where non of the buttons or lamps worked. I was able to fix it, just posting the repair log here in case anyone get the same fault. When I pressed any buttons, there was no reaction to the game. I checked LEDs on I/O board, and they did not lit up at all. I tried with a working CPU board, and then everything worked, so I knew the fault was on the CPU board.

After studying schematics I found out the supply voltage for the I/O board:
* 8Vac (mother board connector 17+U)
* 15Vdc (mother board connector 18+V)
* Common 0V (mother board connector (2+B)

The 15Vdc voltage was missing on the defective CPU board. I further studied schematics and found out the 15Vdc comes from rectifying diode D7 (1N4001) with capasitor C2 (2000uF). They are placed just below the small transformer. I meassured 8Vac supplied into diode D7, but no 15Vdc out of the diode. Therefor the diode must be defective.

Diode D7 was replaced. I did not have 1N4001 in stock, but had 1N4007, so I used IN4007 instead of 1N4001. Power supplied to machine and problem is solved. Buttons and lamps workes again.

Hope this repair log will help someone at some time. -Erik