68kMLA Classic Interface

This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.

Click here to select a new forum.

Macintosh IIsi - Issues after boot

Posted by: MegaImg on 2025-06-05 17:56:44 Working on a Macintosh IIsi for a client. The logic board and power supply unit (PSU) have been recapped. The unit starts up and boots perfectly, but after a couple of minutes, a white screen appears with some bars. The machine has to be powered down manually. I check my work; everything checks OK. Remove the additional memory, test, and remove the add-on ROM, same behavior. Any idea! If the machine is cold, it will work for around 4 minutes.

Posted by: finkmac on 2025-06-05 20:39:19 sounds like the power supply is screwy. double check the little daughterboard on it. ensure you've cleaned all the leaked capacitor fluid.

Posted by: Boctor on 2025-06-05 22:49:37 Do you have a bench power supply of any kind? ATX->10pin adapter? I'd second the PSU suggestion, and test with a known good one, just to quickly confirm whether the PSU has the fault.

Posted by: Callan on 2025-06-06 07:58:43 I've had tons of problems with iisi power supplies, so i'd tend to agree too. If you have an iici (or model with the same power supple) its plug and play to test with. It's obviously heat related since you're getting 4 mins cold. If it ends up not being the power supply I'd get you a can of cold spray and work my way through the cap areas first .

Posted by: volvo242gt on 2025-06-06 13:19:04 IIRC, you can also subsitute a IIci power supply to test the board with. But, yeah, sounds like something's still not right with the power supply.

1