HP 41C display problem

[Alexander Oestert]

Hi experts!

I have recently acquired a 41C, serial No. 1947..., with a screwed on CPU PCB, so not easily removed.

Keying in numbers or letters shows something like this

The flaw occurs on the third position from the left, its shape depending on the number/character I'm keying in on the first (!) position. Most characters give something like an R shape on the third position, characters like "I", "J", "1" or "7" will produce a more slender shape in the third display position. In any case there is also an underscore in the second position and some semicolon and points all around. If this is too hard to understand I will make a video... ;)

I've helped myself by putting a program on a key in USER mode that shifts the display by four alpha spaces to the right. But this is not very convenient.

Does anyone know what can be done against this? Is it a matter of (ultra sonic) cleaning the keyboard and display? Is the graphic engine gone for good?

Thanks in advance!

[Raymond Del Tondo]

Two causes come to mind:

- contact problem of either CPU pcb and/or LCD tray pcb

- defective LCD driver

In any case, you may have to remove the CPU pcb and check the contacts.

Often there is some acid residue (or corrosion, the green stuff) from leaked batteries.

Also check the contact points between the LCD and the kbd pcb.

I had various of the old units where at least one of the metal strips had gone loose.

HTH

Ray

[Alexander Oestert]

Thanks, I will follow your hints!

A.

[Alexander Oestert]

I disconnected the CPU PCB from the keyboard PCB and found it clean. Nevertheless I cleaned it with isopropyl alcohol.

Then, I found the leftmost (looked at from the back) of the connections between the LCD and the keyboard PCB to be loose. I soldered it back on to the keyboard PCB, but there seems to be no lead coming from the soldering point on the keyboard PCB. It looks like I soldered it to the PCB plastic?!?! Should there be something?

Edited: 11 Aug 2011, 5:19 a.m.

[Raymond Del Tondo]

No, depending on the revision of the LCD pcb,
there won't even be a metal bridge;-)