As seems to be typical with Apple IIc purchases these days, mine came without the external power supply. I have ordered some 7-pin female DIN plugs and other adapters that will let me plug a modern laptop power supply (in my case, a standard ThinkPad 20 V 65 W PSU) into the IIc power connector, but these will take a few weeks to arrive and I'd like to use the IIc safely in the meantime, if possible, while not doing anything that's likely to cause a short circuit.
The male DIN jack, documented on p. 234 of the Apple IIc Technical Reference Manual on which one is to deliver +9 V to +20 V has enough room to fit one alligator clip, which could be connected either to pins 2 and/or 3 (signal ground) or 5 and/or 6 (+V). (All pin numbers given here on this connector use the numbering from the Apple manual, not standard DIN pin numbering.) It's not clear if it's touching one or both pins, but since the adjacent pins seem to be shorted together, and it's definitely not touching the other pins on either side, it shouldn't matter which one/both it's touching.
That gets us one of ground or +V. However, finding another accessible location to which one could hook an alligator clip for its counterpart is difficult in the cramped space when the disk drive and PSU are installed. Looking at the bottom of page 2 of the schematics I see the following:
Here CCC and EEE are the ground and +V pins on the DIN connector, and FFF goes off to pin 12 on the "internal voltage converter" (the PSU providing regulated +5, +12, -12 and -5 V power) card edge connector. The switch physically looks like this:
Using a continuity tester, I've confirmed that the bottom, middle and top connections to the switch in the photo above are poles 1, 2 and 3 in the schematic. When the switch is in the off position, connecting pole 2/FFF to pole 3, pin 12 on the voltage converter edge connector is connected to +V on the DIN connector. When the switch is in the on position, connecting pole 2/FFF to ground, pin 12 on the voltage converter edge connector is connected to the ground pins on the DIN connector.
Since the connection to switch pole 3 is easily accessible to attach an alligator clip to without danger of shorting anything, my current plan is to connect +15 V from a regulated (bench) power supply to that and clip the 0 V side of same supply to pins 2/3 on the DIN power connector, like so:
This will, however, bypass both 10 A fuse F1 and inductor L1. I suspect that bypassing the fuse will make no difference since my bench supply won't deliver more than 5 A. (It goes into constant-current mode if asked to deliver more than that, which will cause the voltage to drop dramatically, which in turn should cause the voltage converter to shut down, according to the Apple manual). I have no real idea about the inductor, which you can see in the photo above as the big black cylinder next to the capacitor, but I suspect it's there merely for noise suppression.
Is what I'm proposing to do here likely to work ok? What are the risks associated with it? Can anybody think of a better way to connect power to this short of waiting for my 7-pin DIN connector to arrive and soldering up a proper cable?