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IIsi and IIci Power Problem Troubleshooting


Well-known member
My IIsi and IIci are both having trouble booting, with the same symptoms. Both systems worked when I put them in storage about 2 years ago. Both logic boards have been recapped. The IIsi power supply was also partly recapped. I don't remember about the IIci power supply.

When the power button or keyboard power key is pressed, the computers repeatedly turn on and off a couple of times per second. After many attempts I did finally get the IIsi to boot, and it runs for a while, but then spontaneously turns off after 5 minutes or so. And if I do a normal shutdown from the Finder menu, the IIsi reboots instead of shutting down.

Any suggestions where to start looking? Is this a likely PSU problem, or maybe something else?  



Well-known member
The ATX power supply works! At least on the IIsi - I haven't tried the Iici yet. The only problem is that the IIsi audio doesn't work, but I don't think that's related to the power supply. As I recall, the IIsi speaker contacts are prone to corrosion.

What I did was get an 8-inch ATX extension cable, 24-pin to 24-pin, and rearranged the wires on one end to match the Mac power supply pinout. Then I hacked off part of the connector to make it a 10-pin instead of 24-pin. I didn't bother to hook up the soft power circuit, but I saw plans in another thread for doing that. For now the Mac turns on and off with the ATX power supply's built in switch.

Now that I know it's definitely a power supply problem, I can move ahead with recapping the original supply, or maybe I'll just live with this ATX solution for a while.





I'm wondering if my ancient WAGs about IIsi/soft power/ATX might be of help?

Suggestion: test wiring the AC input and ATX soft power setup of your PSU to run through the IIsi's AC input board adapter. Se if that fixes your soft power problems. If that doesn't work, you could fix the IIci PSU first and use an ATX extension straight thru from IIci PSU to IIsi board. Had I known about that trick seven years ago the metal can of one of my spare Q700 PSUs would still be intact. But I rather like its nasty hacked appearance. :lol:

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