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

[damaltor]

Harald: Will do, though I have already plugged a memory module in which works fine. I dont know if a memory module uses all Voltages though.

BobVA: I thought of that too. Who would drive a motor via zebra strips?? That is hilarious. But I don't think that this could be the problem, as the calculator malfunctions if I just plug the reader in it, I do not even have to switch it on or actually use the reader. Also it does not get better after removing the reader. Good idea though!