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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.

Apple IIc power input connector with alligator clip

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:

Apple IIc power input schematic

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:

Apple IIc power switch

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:

Proposed power connection

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?

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  • What you're proposing appears likely to be ok, at least for the short term. And yes, your bench supply is likely to provide cleaner power than you'd get with the original power supply so skipping the inductor is probably harmless. But if it were me I'd put some test clips on the back of the DIN connector and hook up that way. Here's a link for the kind of test clips I mean (not a recommendation for this seller, just the first link I found) amazon.com/Elenco-Electronics-TL-21-Grabber-YELLOW/dp/…
    – Ken Gober
    Nov 5, 2019 at 13:36
  • @Ken I've got a set of cables with banana plugs on one end (perfect for connecting to my bench PSU) and those test clips on the other. But the pins in the DIN jack are quite a bit larger than what the clips are designed to grab. Between that and the rounded ends of the pins, even when you can get them attached they pop off if touched with more than the slightest pressure.
    – cjs
    Nov 5, 2019 at 13:49
  • I also tried the more traditional alligator clips but it's really easy with those to touch the clip to the metal ring surrounding the the pins, which would short +15 V to ground. (The alligator clips I use in the post above are fully covered in plastic on one side, preventing that.)
    – cjs
    Nov 5, 2019 at 13:49
  • That's why I like the hooks, and why I recommend attaching to the back of the connector. The leads from the connector to the board are usually easier to get a hook securely fastened to.
    – Ken Gober
    Nov 7, 2019 at 3:47
  • @Ken Just to be clear, you are saying you like the hooks with the understanding that they disconnect if the cable is moved even slightly, right? (Or have you tried hooks on a male DIN pin and had better results than me? If so, perhaps you could post an answer with a photo of how you got that to work?)
    – cjs
    Nov 7, 2019 at 5:07

1 Answer 1

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If you're really willing to do some jiggery-pokery, find some small gauge solid copper wire (like the twisted pairs from a CAT5 cable - I like to cannibalize old multi-conductor telecom cables) and get yourself two longish bits of wire. Strip the insulation back about 1 inch on one end of both wires.

Now find a toothpick or something very close to the diameter of the pins on the DIN connector. You want a diameter that is just a little bit smaller than the DIN pins. Twist the 1" copper around the enlarged toothpick like you are wire-wrapping a board.

You should have something similar to this:

twisted wire end

Now you can slide the improvised connector over one of the pins of the DIN. If you are careful, and lucky, friction will hold the improvised connector on the pin giving you an 'extension' you can easily connect an alligator clip to on the other end.

This is a quick example. It's the wrong connector, but the principle is the same...

a random example

Of course ALWAYS visually inspect your work and ring it out to make sure you are not shorting anything.

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  • Well, this does work, though it produces a quite noticable spark at the PSU output when I plug in the banana connector, even though the Apple's power switch is in the off position. (The Apple IIc still draws about 35 mA of current at 15 V even when it's powered off. When off, the +V power input is connected to a single pin on the PSU card connector via line FFF in the schematic above.) Because of that, I think I probably wouldn't recommend this unless you have a switch on your external PSU. (The manual for my bench PSU says it ought not to be powered up with a load.)
    – cjs
    Nov 7, 2019 at 9:48

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