Macintosh II Power Supply Questions

[Busterswt]

Hello all,

Recently picked up a Macintosh II (Rev A, I think) and am attempting to get it setup with System 7.1 Pro. I had success installed 7.1 on a MacSD scsi emulator, but over the last week I've experienced some oddities with relation to SCSI, specifically "locking up" during writes. At first I chalked this up to the scsi emulator after having performed a firmware update, but today I happened to notice that the power supply fan was not running and the power supply case itself was very hot to the touch after the machine had locked up/frozen during a finder copy operation. I've been running with the lid off to negotiate sd card swaps.

Anyway, just curious to know if the fan is variable or should run at some constant speed all the time. Also, is any sort of recap necessary on these power supplies?

Thanks for your time.

 

[markkrueg]

I also have a Rev A Mac II. The fan is quite loud on those and runs continuous (not variable). It cools the entire system, so is important. I recently removed and opened my power supply. The fan is connected to a pretty standard 2 pin header. I connected a larger 12v fan and zip tied it outside the PSU. I did this because it’s a much quieter fan. It’s working well for me, but long term I would like to find a correctly sized replacement.

Note that working inside the power supply can be dangerous, and the large caps can hold a lot of charge.

Removing the fan is a bit tricky. You should un-bolt the white plastic cable clip shown at the top of the first photo. This will let you move those cables around and then you can carefully angle the fan out of position and remove it from the PSU. It sits on that square plastic piece shown in the third photo.

 

[markkrueg]

Here is what my temporary fan mod looks like. It’s not great; as I’m running the PSU without its cover (not safe). But it’s running smoothly for now. Note the orientation (air flow arrows on top of the fan). It is blowing air from inside the case through the power supply and then out the side vents of the case. This is the same orientation as the original fan.