One of my 41's doesn't like modules in port 4

[BobVA]

(05-07-2016 08:07 PM)damaltor Wrote:  Interesting. I am a bit scared to open it though, because it is one of the very early ones with the delicate connection between the pcbs.

I had a similar problem with an HP-41 that refused to work with a card reader which turned out to be a defective pcb interconnect. The current to drive the motor runs though the interconnector. The elastomeric/"zebra" types are prone to developing high resistance.