Macintosh II - powers on immediately

[egrath]

Hi,

I have a Macintosh II here that I got as DOA. Recapped and cleaned everything, looks good so far. However, one issue remains:

The device powers on as soon as voltage is supplied to the power supply. Also Soft-Power-Off does not work.

Any hints on what I can check first?

With kind regards,
Egon

 

[blturner]

This writeup is the main reference I'm using for Mac II's with power issues: https://www.downtowndougbrown.com/2015/03/explanation-of-the-macintosh-iiiix-power-onoff-circuit/

Another great resource is over on TinkerDifferent by @David Cook https://tinkerdifferent.com/threads/macintosh-ii-advanced-diagnostic-techniques.5020/

 

[egrath]

Thanks for the link, I'll take a look into it!

 

[egrath]

Can anyone please tell me if a voltage output of 2.8V on UB2, Pin 3 is normal when batteries are inserted, but the logicboard is otherwise don't connected. I measure from B2 negative to the UB2 Pin 3.

And is it normal that when measuring from B1 negative to UB2 Pin 3 that there is no voltage difference at all?

And one additional question: Does someone know the pinout of SW1 and how to check if it's hanging?