Mac II/IIfx fan

[beachycove]

I have a Mac II that was converted to a IIfx, complete with sticker, at some point in the early 90s. It has the loud II power supply fan. The IIfx had a variable speed fan and was much quieter.

Does anyone know if a variable speed fan can be straightforwardly installed in the Mac II PS, or is there new circuitry required?

[IIfx]

I do believe there is new thermal detection circuitry in the IIfx PSU. Be aware that if you have a lot of power sucking cards, the PSU will be loud very quickly.
I think that the old single-speed fan is better for reliability and total cooling.

[zuiko21]

Can't say for sure because I haven't finished my hack yet, but... since the connector on both PSUs is very much the same (you're have connected a II PSU on a IIfx board, indeed) I don't think the IIfx has any way to "send information" to the PSU's fan (no spare pin!) so the fan speed control should be in the PSU itself.

All the large machines in the Mac II series (the II, IIx and, I presume, the IIfx too) have a thermal shutdown device on the motherboard, as a safety measure against overheating, but that's all-or-nothing.

(Someone please correct me if I'm wrong)