IIsi start issue

slicknick13

New member
Didn’t see anyone else with the same problem after a search so here goes:

Recapped my logic board and power supply and had an issue where the computer wouldn’t stay on. This got worse and worse until I ended up where I am today, the computer won’t latch on at all.

I thought it was the power supply as the daughter card was pretty mangled when I capped the PS, but then I just put a caymac supply in with the same symptoms.

If I hold the power button on the back of the machine on, it will cycle the supply on and off, checking the output of the 6805, I can see the pfw signal output to start the computer and I can also see the 5v from the supply coming through the diode that I imagine is latching the signal on. What I guess is happening is that pfw is getting pulled back low by the 6805 but why? I imagine it’s not liking what it’s seeing or I’m not catching the watchdog in time.

I can short the trickle supply and the pfw and I do get a chime for what that’s worth.
 
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