Recapped Macintosh IIsi powers on, but won’t power down unless unplugged

[VeryVon]

Hello, I just recapped a Mac IIsi and its power supply. It powers on and operates perfectly, but when I shut it down it powers back on immediately. I can reset it with the power switch, but it’s constantly stuck in power on mode.

I’ve checked over the motherboard, triple checked the capacitor polarities, re-disassembled the power supply and scrutinized there as well.

I tracked down some schematics to discern likely what failed, but have a hard time reading the circuit.

There’s a “power monitor line” that supplies a +5v 1ma trickle to the power supply (I just know this because of the comments on the schematic) which looks to be pulled low by the power switch.

Any ideas on which component(s) may have failed in this circuit?

 

[VeryVon]

Just to close this thread out, I took the power supply apart again, de-soldered the vertical sub-board and cleaned up solder on the recap job. It looked fine, but afterwards the problem is fixed. There may have been a short to ground on one leg of one of the caps.

 

[3lectr1c]

that's the soft power board and they're very picky. most of the time you have to desolder chips and clean under to get it working reliably, very bad spot for cap leakage. Good to hear that you got yours going.