Missing segments on LCD of HP41C



#5

I'm trying to repair the very much loved HP41C of a coworker. At first it wouldn't even turn on. This could easily be solved by cleaning the inter-PCB contacts. But even before the HP quit service the LCD wasn't working properly. I assume a bad contact between LCD-PCB and glass. Actually I noticed a change in the contrast of several segments over short periods of time. I think I'll need to solder another LCD to the keyboard-PCB. Has anyone attempted to do this? Does anybody have a broken HP41C (CPU bad) with good LCD? Many thanks for your help.
Cheers Daniel


#6

It is quite easy to change out the '41 LCD modules. Just unsolder the pin contacts from the keyboard and the module can be tilted out and replaced. Use as little heat as possible to keep from unsoldering the end of the pin that connects to the LCD module (they are a bit of a pain to put back). If you don't have a solder pump you might try sliding an exacto knife blade under each pin as you go. Be careful not to touch the soldering iron to the front screw posts. They are close to some of the pins.

You might even want to try opening up the LCD module and cleaning the contacts. The instructions for doing this are in the '41 service manual available on the HPMUSEUM CD ROMS or the HP41.ORG web site.

#7

It's not hard to remove the LCD module from a non-halfnut machine (which is what this sounds like). Take it apart as usueal, remove the little support strip at the top edge of the display,
desolder the contacts from the keyboard PCB and remove the complete display module. Be warned that the display drivers are CMOS and static-sensitive.
Once you've got the display module out, it's worth trying to repair it by uncliping the clips on the long sides of the module. Then the LCD glass will come off the hybrid, they're connected by zebra-strip connectors. Clean all the contains (LCD glass, PCB, zebrastrips)
with propan-2-ol, and put it all back togther. You might find the segments work again.


#8

David, Tony,
Many thanks for your help. The LCD works again like new. I tested it with the PPC function 'DT'. My coworker was highly delighted. He said this was a souvenir from the University in USA before he came to work in Switzerland.
Cheers Daniel


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