HP-41C Shows 12 Commas, Otherwise Unresponsive

[burkhard]

Good picture!
This must be a quite early 41C because it shows two nuts around the lower black posts, holding the daughter board onto the main board. The later versions of the 41 series don't have those nuts and only squeeze the daughterboard onto the main board with the skinny screws going into those two plastic posts. With age and use/abuse, the plastic posts crack and the "squeeze" is no longer so good, which causes all kinds are weird behavior because of the poor contact between the boards.

For yours, though, those two nuts *might* be holding things tight... I think they can be removed the get the daughterboard off at which point you could clean the contacts between the two and apply some DeOxit Gold. But.... I haven't taken apart one this old with those nuts myself and don't know if there are special cautions. You obviously do not want to break either of those two plastic posts off...

So, let's let somebody reply who has disassembled one of these early ones with the daughterboard nuts.