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

[AndiGer]

Hi Karel,

IIRC once had a similar issue. It was corrosion on the I/O port. Those days I sent Diego some pictures and he discovered the fault that I could repair with some soldering.

So check the I/O port thoroughly.

Andi

[Karel]

Thank you Andi.

The 41cx got port block from 41c for the time being. I am waiting for new ribbon from calculator store to repair the block for 41cx. It had bad battery leak. I cleaned the board thoug.
The 41c tallkey fullnut was in bad shape as well but no leakage as far as I can tell. I used its port block in 41cx while working on the 41c keyboard and display board.
The display was badly soldered on and there were snots of solder everywhere. It must have shortened some traces - the display was faulty. Few segments missing.

K.

[AndiGer]

I found the picture where one can see the faulty connection

[Karel]

Yep. Thank you for your effort!

I took out magnifying glass and found some green stuff on the module connector.

Yuck!

All the best,

Karel

[David Hayden]

At the risk of stating the obvious, I assume you're aware of the gummy wheel problem? A gummy wheel might cause the symptom you describe. Insert card, gum prevents wheel from spinning. Motor sucks too much current. Voltage drops. Memory lost.

[Karel]

Thank you David.
I am aware of the wheel issue. Already got some material for repair just in case.

It is now in the state that when I plug in the reader, it is recognized by the calc. I can do catalog 2 on it.
When i insert a card, it starts behave wrongly. But I do not hear or feel the motor trying to spin.

[David Hayden]

(11-21-2023 09:10 PM)Karel Wrote:  Thank you David.
I am aware of the wheel issue. Already got some material for repair just in case.

It is now in the state that when I plug in the reader, it is recognized by the calc. I can do catalog 2 on it.
When i insert a card, it starts behave wrongly. But I do not hear or feel the motor trying to spin.

I'm certainly no expert, but your symptoms seem consistent with a gummy wheel that's preventing the motor from spinning. EVERY card reader drive wheel turns into gunk, so if it hasn't been repaired, it needs to be. Note that you should repair the dampening couple that holds the worm gear to the drive motor axle at the same time. It's made of the same gunk.

[Karel]

Thank you again, David.

You are right. I opened the reader and foud deteriorated gummy wheel indeed.
I cleaned everything and I am now searching for right size of wire insulations to repair the coupling between motor shaft and worm gear.
As seen in this thread:
https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=163396

Karel

[David Hayden]

(11-27-2023 04:19 PM)Karel Wrote:  Thank you again, David.

You are right. I opened the reader and foud deteriorated gummy wheel indeed.
I cleaned everything and I am now searching for right size of wire insulations to repair the coupling between motor shaft and worm gear.
As seen in this thread:
https://www.hpmuseum.org/cgi-sys/cgiwrap...ead=163396

Karel

If you have a drill press, consider the method described here starting on page 41.

[Karel]

Thanks!
I finished the repair. I used some wire insulation on motor shaft. It made the shaft almost the same diameter as the worm gear. Still smaller than the inner dia of alu tube. I then used some shrink wrap to build the diameter and connect the shaft and worm gear together. Pressed the assembly into the tube. Secured the worm gear end with tiny amount of E6000 glue.
The reader worked fine but intermittently. So I remembered what AndyGer wrote in his reply to this thread and checked the ribbon contacts. :-(

I got two 41 calc. One was halfnut CX described as for repair. It had badly corroded contacts. The other was C fullnut. Described as working. But when I got it the display was erratic. I disassembled it and used the battery connector block temporarily in the other one - the CX because it looked fine (seen from the side of battery contacts). Have not noticed the gunk on module contacts. Anyway, the infected trace seems to be cracked as well and that is probably the reason of erratic behavior after repair.
The fullnut 41C that was supposed to be working was previously heavily and not very profesionally repaired. I found the battery block glued with ca glue to back part of the case and under it broken post glued with crazy glue as well. That fell off with tiny amount of force. Lower posts where the processor board is located were smeared with superglue too and the spacer block under zebra contacts was glued to those posts. All and all bigger project than I thought.
I need to wrap new ribbon contacts around the two connector blocks first. Then repair the back case with new "improved" posts. I did not know that when I ordered the ribbon contacts from calculator store. So I am in the phase of contemplating of either placing new order or modeling and printing them myself.