Bad HP41 display? Shows @'s and whistles

[mfleming]

Thanks everyone for the suggestions. I'm struggling to restore three "for parts" 41CVs with questionable zebra connectors. A couple worked for a while, then went intermittent - sometimes worked, sometimes not. In swapping out suspect parts one at a time, I may have zapped one of the CPU boards. I've put that board aside and I'm using another one that works fine, which I think rules out the display. I've found the zebra connector to be a constant source of headaches, so much so that I never again open a calculator once I get it working

Quote:Is there a source for golden zebra replacements or substitute for reasonable prices? Or solder all contacts from keyboard to mainboard as I have seen somewhere (Monte and the 41CL?)

I got into this fix a couple of months ago with a flaky 41C (zebra again!). I tried the soldered wirewrap approach and made a complete mess of it. Wires constantly popping off cold solder joints and/or breaking off when flexed. That calc now lies abandoned in a junk bag in hope it can be resurrected in the future, when science finds a cure for bumbled repairs.

It did inspire an effort to find a substitute for the zebra connector. After a couple of failed approaches, I have a third replacement approach that seems to work. I've managed to successfully replace the zebra connector on two of the three calculators, and I'm working on getting a repeatable and reliable replacement process worked out. The principle is simple, but the details are anything but.

       

The two images show the basic idea; In the first image, a flex circuit with gold contacts carries the signals from the keyboard PCB to the CPU PCB. The second image shows the flex installed, ready to be folded over to make contact with the underside of the CPU board. Two lengths of lamp cord are held in place over the lower contacts with two-sided tape. The cords serve to press the top and bottom flex contacts to their corresponding PCB contacts. This is where all the trial and error with materials comes into play.

The two gold zebra connectors in the first photo are now spare parts. Hopefully soon I'll reach a point where all this will be useful to others.

Well, back to the bench...
~ Mark