The power supplies had a couple obviously bad capacitors. I didn't bother shotgun replacing them. The owner wanted to outright replace the PSUs with modern ones.
The Macintosh II line however puts +3..6.5V from the internal batteries onto the power supply's /PFW line. Once the power supply started up, the circuitry keeps this line high with power from the supply.
Seems a bit convoluted, but it boils down to having to invert the /PFW line using the standby power provided by the ATX supply.
Seems a bit convoluted, but it boils down to having to invert the /PFW line using the standby power provided by the ATX supply.
A simple bipolar transistor will do the trick. I chose a BC548C NPN, simply because I have a lot of them.
Some napkin math lead me to pick 10k for the base resistor and 470 Ohms for the collector. The +5V come from the standby power.
Some napkin math lead me to pick 10k for the base resistor and 470 Ohms for the collector. The +5V come from the standby power.
Ok I think I need some help. The idea was to use the HDD from the IIfx to boot and test the other macs as those came without any hard drives. I kinda misplaced the ROM module of the IIsi, so IIvx it is for now. It doesn't want to boot this HDD. Can you even do that? Is there a floppy image I can write to test these machines?
Ok I'm a bit of a dum dum. This is a 32bit CPU and needs all four RAM Simms populated. Boots now.
The onboard graphics however seemed to be bad. With a pattern that changed if I swapped the VRAM modules around. The ICs on there are ordinary DRAM.
After trying a different video cable it works though. Except the resolution is so weird that even the LCD cannot properly display it, without messing with every setting of that monitor. My CRT is still hopelessly confused. Ahhh, Apple
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That's pretty cool. Too bad that the mechanism in the other drive is jammed.