The CoCo wiki project was started on October 29, 2004. --OS-9 Al

From CoCopedia

I don't know how many versions were made, but mine runs off a single +5 volt supply. It does not use batteries to get the programming voltage, it uses a DC-to-DC voltage contverter to generate the +12V, +21V, or +25V programming voltage. By using a DC-to-DC converter, it allows it to work on all versions of the coco. This IS compatable with the CoCo3.

repair tip: I had my DC-to-DC converter go bad (I broke it, by overloading it, it was an accident), and I simply tested the 4 transistors and replaced the bad one(s). With the price of these small signal transistors, you're probably better off to just replace all of them.

I will try to get a picture of mine posted before too long. Someone contact me if I forget.