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i disassembled my 41cx, help! - Printable Version

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i disassembled my 41cx, help! - David E - 11-15-2002

I took off the cover to clean a few of the contacts with an eraser as they were corroding, but now all bolted up again, it doesn't work!! I have only 2 CPU board to keyboard interconnect, is this correct, or did I loose one? also does it matter what direction they are placed. I cant think of anything else I may have screwed up :(

any help is appreciated.


Re: i disassembled my 41cx, help! - Vieira, Luiz C. (Brazil) - 11-15-2002


first of all, DON'T PANIC! Let's see what's going on.

You have the mainboard and the keyboard, so you have a fullnut HP41CX. What sort of connectors do you have between the mainboard and the keyboard? I know three different types of connectors and all of them go between these boards:

i - one of them consists of two tubular polymer and very-thin-trails zebra connectors built with an isolating sort of tape;
ii - the other consists of a pair of foam with not-so-thin-trails zebra connectors around them; in this case, the plastic separator built in the screw posts has four extensions, to guide the foam so it stays in position
iii - the last one resembles a conductive polymer, but it has a lot of thin conductors that once fold will hardly connect the boards.

Silly reasoning: in the last two cases, the conductors may be placed in a bad position OR rotated, what will not allow both main- and keyboard to connect with each other. Would you check for this, if you have not already done it?

Also, the "pressure" that keeps both PCB's and the connector between them comes from two different points in two different assembles:

i - one that has two big nuts around the screw posts; these nuts are directly "screwed" around the post itself, and keep enough pressure so both PCB's can "talk" to each other;
ii - the other uses the case screws to keep the physical pressure that maintain the contact between the two PCB's.

The best assy, for me, is the first one, because the nuts will keep the calculator working even when the case screws are not completely screwed. In the second case, if the threads of the PCB's posts are loose and the screws are failing to keep pressure, the calculator will often have contact problems.

Taking care with the posts is the best we can do; checking for cracks or any fatigue signal. Many techniques to rebuild these threads and the posts themselves were described by the collaborators in here. You should give us some info so we can focus on your particular solution.

Also, you may read (if you haven't already) this article because it contains descriptions about how to disassemble and reassemble an HP41CX. The method of soldering the two PCB's is effective and should work, but trying to keep the connector between them allows faster PCB's trading, when necessary.

I know this is more information only, but I'm waiting for a more detailed description of your 41CX's internals.


Re: i disassembled my 41cx, help! - David - 11-15-2002

thanks for the advice. I took some plastic washers from my other hp41C, and used them, and now it works. I about had a heart attack, as the CX was recently purchased. I don't know what the problem was, but it works now. It must have been the pressure. If this happens again, or frequently, perhaps I will just hard wire the thing, like the howto on this site says.


Re: i disassembled my 41cx, help! - Vieira, Luiz C. (Brazil) - 11-16-2002

Hi, Dave;

it's always good reading this sort of news!

I'd wriote an e-mail about the subject below, but you never posted yours, so...

Hardwiring both PCB's may sound good, but try doing this ans a last-shot, no-way-out solution. Consider loosing the zebra connectors, breaking the posts in a way you cannot repair, corroded contacts... Well, I'm writing this all because I have another HP41C that I suspect that is ready to work, but I did not find the time to rebuild the very-thin-traill zebra connector that came with this 41C. It's a time consumming activity, and there are others not yet even started, you see?

Well, this is just an advice based on what I would do: try to recover withoput soldering.

If, by any reason, you need to hardwire the PCB's, success!

Best regards.

Re: i disassembled my 41cx, help! - Emmanuel, France - 11-16-2002

I use to fix HP-41s. I think I'll write an article about that (another one because there's several).
For battery contacts, please GTO: