IIsi no soft power

[3lectr1cPPC]

I've just gotten a chance to properly check out the Mac IIsi that I got at the recent VCF East Swap Meet. It has had it's PSU and logic board recapped previously and the work they did looks good. It boots up fine into Mac OS, but has one issue I've seen - soft power isn't working.

It instantly powers on when plugged in, and pressing the rear power button doesn't shut it off. When shutting off in Mac OS, it brings me to the "You may now shut off this Macintosh" screen instead of shutting off. Anyone know what chip or circuit controls soft power? Hopefully it's just a bad trace somewhere or a bit of crap left on the board.

 

[joshc]

Has the power button been turned so that it powers up as soon as power is applied? These have a 'permanently on' setting.

 

[3lectr1cPPC]

Oh crap I'll bet you're right. Soft power did work the first time I plugged it in but I forgot about that setting. I'll try that.

 

[3lectr1cPPC]

Nope, it actually wasn't in that position.

 

[joshc]

So it depends if they did a full recap of the PSU or not. If it's the Sony unit, there is a small daughterboard in there which handles the soft power stuff.

Macintosh IIsi Power Supply - Recap-a-Mac

The Mac IIsi has a power supply that is extremely prone to leakage. In fact, I’d be very surprised to see any IIsi...

recapamac.com.au

 

[3lectr1cPPC]

Soft power board has been recapped, I checked myself. It looked pretty good when I looked at it but I'll bet that's where my problem would lie. I can get photos of it later but honestly it runs ok without soft power function so I might just leave it as is for now, instead of dealing with the dreaded IIsi power supply.

 

[David Cook]

I have a write-up that describes how to diagnose the motherboard's portion of the soft-power circuit here (starting with the sentence "The other Mac IIsi doesn't respond to the rear power button or the keyboard power button"):

IIsi Repaired By Reheating Solder Joints and Replacing Crystal

I recently bought two Macintosh IIsi computers. Neither worked upon arrival. The initial restoration steps are common: 1. Remove old battery 2. Blow out dust 3. Replace the capacitors on the motherboard and power supply. I decided to replace the big capacitors on the power supply as well. They...

68kmla.org

You can perform the tests without the power supply -- just install a PRAM battery and use a multimeter to test for a pin state change.