This one had some problems with the internal batteries when I first got it but it ran like a champ on the external power input (which I found out from Jerry is wired around the power switch). I replaced the internal batteries myself the first time but pulled a tiny wire out while doing it. He moved a couple of things around while he was under the hood but it seems to have happened again.
Mine has all the components encased in epoxy. Hopefully I can fix what's wrong with it by figuring out how to get the boards out to get to the power section and see if there's a broken solder connection and loose wire down there. If not, I know someone in town who may be able to take a look at it for me. He fixed my SD 442 for less than half of what SD was asking just to bench it. His main gig is vintage hifi audio - power amps, classic receivers, tape decks, etc.