Growing up, I never had any interest in the TRS-80 MC-10. It was underpowered and had a terrible little keyboard compared to its bigger brother the CoCo. I would poke around on one now and then at Radio Shack but it never really had much interest to me. But since I've been lurking in lots of retrocomputing corners of the internet lately, I keep seeing them pop up and people are still doing interesting things with them. So when I saw a super cheap one on Craigslist, with the 16K RAM pack, cassette cable, and video cable included, I couldn't resist. Unfortunately, what wasn't included was the power supply.
Normally a missing power supply would be no big deal. I've already got a few universal power adapters that I've been using for my Model 102, CCR-82, and PC-3 Printer. But the MC-10 is a weird little machine. It actually requires an 8V AC adapter, not DC. I did some googling and found posting in a forum that said DC would work fine, but the RS-232 port wouldn't work. I couldn't find anything to substantiate this claim but I did eventually look at the service manual and it does look like the circuitry should handle DC voltage just fine. It basically runs the AC through a recitifier to convert it to DC anyway. The service manual states that "a small amount of negative voltage is required to the RS-232 output op-amp" which you can see in the lower part of the circuit diagram above. "Vee" represents the negative voltage. In the full schematic, unless I'm missing something, the only place Vee is used is indeed an op-amp that makes up part of the RS-232 port. So in theory, as long as I don't use the RS-232 port, it should work okay on DC. . So I decided to give it try and, sure enough it boots up fine.
I do still plan to get the correct AC power supply at some point. My local Guitar Center has one that should work but that's considerably more than I paid for the MC-10 itself. A lot of people suggest the Atari 400/800 power supply is a good replacement so I may go with that, or I might try my luck on ebay but for now it's good enough to mess around with. It is also in pretty rough shape (this picture actually looks better than it does in person) so I think I'll take it apart and give it a good cleaning and try to retrobrite the case, which seems to be all the rage with the kids today.