HP41 card reader repair

[Karel]

Hello everyone.

A newbie here.

I am in the middle of repairing of two 41's and one card reader.
I got the reader from ebay today. Put it in working 41cx with fresh batteries. It sometimes does not switch on, sometimes does.
When I put a card in a slot, the calculator goes off and then "memory lost".
The reader is visualy intact. I am sure it was never opened.

Anyone got some hints what the possible problem might be? Looks like a short of some kind to me.

Also, I completely disassembled (including keyboard) one of the 41's - it is full nut tall keys 41c. I might post some pics of why I did it. Do you think it is a good idea to replace the tape covering the key domes with fresh one, maybe kapton?
Would like to clean the whole thing thoroughly.

Thank you in advance!

Karel