41CV Repair Service



#3

Does anyone know on this board whether HP still service their vintage product like 41CV calculator? If yes, what is their web site address, and phone number?

I searched HP web site, but I could not locate any info on 41CV at all?

Thanks.


#4

I did not mention in my original post why did I need service to my 41CV?

The condition of my 41CV is just like I opened it from the brand new box just came out from the factory even though I bought it in 1983. It has been just well kept. No corrusion in the battery terminal at all. A few months ago when I tried to turn the calculator on, it did not come on. Immediately I changed the batteries, still did not come on. What a disappointment? I guarded this calculator with my life all this time, now I'm at a loss. That is the reason I posted the original message.

If there are any 41CV technical expert on this board, your help or suggestion would be greatly appreciated.

#5

... HP no longer support the HP41. But you may read this post first:

HP41 Gone Wild!

It's not the same situation as yours, but the first steps you should take in order to repair (at least start) are described there. Please, read the posts in that thread and reson about the mentioned procedures. Also, check if your HP41 is a fullnut or a halfnut.

Chances are we can get your HP41 repaired if you have the skills to delve into the solution.

Best regards and success.

Luiz C. Vieira - Brazil


#6

Luiz,
I think I found the problem. I unplugged all four modules from the compartments, then I cleaned them with ethylene alcohol and dried them, and then plugged all the modules back. Then put the battery chamber back in and turned the power on. Nothing happened. Then I put the calculator back on the table and hold it by left hand and turned the power on by right hand. It came back on. As soon as I lifted my left hand power went away. I pressed with my left hand again, power came back. After I searched through I found out that the left bottom corner is no longer snuggly fit the back layer of the calculator from the keyboard layer of the calculator. They are coming loose.

However, I could not see any screw anywhere. Screws are not visible at all from the outside. And I don't have any service manual for how to take a part without damaging it. Do you know how to get to that screw? Anyone? Can any hardware expert guide me through this operation? If can give me a link for step by step operation would be highly appreciated.

John


#7

As it says on the cover of a great book, "DON'T PANIC"

The screws are under the rubber feet. Peel them off carefully and stick them on the paper that stickers come on, like the ones that come with a video cassette. The feet are actually made with two layers: the outer one is rubber and the inner one is thinner vinyl. Peel the vinyl layer from the plastic case.

More help is on the way!

#8

The HP41 is assembled using connectors that are clamped together by the case -- if this is older ('Fullnut') unit, there's a connector between the logic board and the keyboard PCB at the front of the machine. All machines have a connector between the 'I/O assembly' (the battery contacts and the module connectors) and the keyboard PCB.
The case is held together by 4 self-tapping screws under the feet. Peel off the feet and remove the screws. Carefully separate the case parts, and clean the contacts with propan-2-ol (ispropyl alcohol). Then put it all back together. Don't overtighten the screws, but you do need to ensure the case is clamped together tightly. It often helps to turn the screw 'backwards' (counterclockwise) so as to engage the original threads before
tightening them -- this will reduce the risk of stripping the threads in the plastic case.
If the threads are stripped, or the plastic pillars in the top (keyboard part) of the case are damaged, then often all you need to do is fit a longer screw (it's a #2 self tapping screw), which I suspect you can get from a local hardware shop.
Oh yes, please take anti-static precautions when working insde the 41 -- this machine uses relatively delicate CMOS circuitry, and _all_ the chips are HP custom and unobtainable.


#9

If the plastic pillars are cracked, and this is causing the screws to be loose, there are some techniques that can be used to repair them. They involve using a solvent that will melt the surface of the plastic. By binding the parts together so the broken edges are in contact, and then applying some solvent, the edges will melt a little and then when the solvent evaporates, the pieces will be welded together - as strong as when they were newly made, I have read. Some people recommend wrapping the pillar with fine wire to make it even stronger, but it must be very fine so the diameter of the pillar is not increased much, or things won't go back together as they should. I think the reason the pillars tend to crack is because HP designed them with a smaller diameter than was most wise. The type of self-tapping screws HP used were new at the time and all the design requirement might not have been known.

The solvent is methylene chloride, also known as dichloromethane. It is sold in small bottles at hobby shops, I found some at a plastic distributor that sells primarily to sign companies.

If the pillars are broken off and not just cracked, there is a contributor here who has a way to replace them with a piece of plastic rod (I think that's what he is describing!)


#10

Thanks, Ellis and Tony. You both are helpful.

John


#11

Luiz, Ellis, and Tony,

I would like to ask a dumb question. Please don't laugh. Just give your honest and expert opinion.

As you all advised for fixing the broken or cracked plastic post, indeed an excellent one. How about if I press and hold the left corner such a way that the display starts to appear, then I apply just enough super glue at the meeting line of the upper and lower case (of that corner and its close proximity) and long enough to dry the super glue completely. Danger that I see of that I won't be able to take a part this calculator again. Is there any other downside for this permanent sealing?

Thanks, and waiting to hear from you.

John


#12

Hello, John;

I am almost sure everybody else will tell you the same: don't!

You'll leave watermarks, it's gonna be almost impossible to open it again without cracking the case and the separator, you'll need to "glue" twice or in both surfaces at the same time, chances are you'll experience the same problem later because you did not actualy solve it... and you're gonna do nothing but cause dammage to your calculator. If the glue leaks to the keyboard or internals it's gonna be hard to clean the mess.

What's bothering you, afterall? If you believe you can't accomplish the task in an easy way, others (me included) will offer to do it. I know, I'm in Brazil, it's a bit far from you, but I succeed repairing some calculators for a few fellows in here. Exception made to Scott Pritchard because I am still working on two of his calculators. And there are others closer to you than I am that would gladly offer themselves to repair your "unit". Mostly because it is working, it's only a craft job you need there.

Please, do not risk it. It "sounds" so easy to repair...

Anyway, if you want to do it, go for it. I would not, and I would never suggest this sort of solution to anyone. I used superglue sometimes to repair broken parts and even to replace broken posts because I did not find the type of glue that people at this forum use. It's a chemical "melting" solution that fuses plastics with each other. But I got good results when broken parts are kept under pressure for about three hours with superglue. And I never used any sort of glue to do this sort of "joining" you are trying to.

Be patient and I am sure you will succeed repairing your HP41 the best way.

Luiz C. Vieira - Brazil

#13

If you are not ready to do the permanent repair now, instead of superglue, why not use a rubber band? If it goes just below the display, or just below the top row of switches, or both, it wouldn't interfere with operation. The top feet would tend to keep it in place. Be sure to keep you programs backed up, because the rubber band might give up at a bad time! (So might the superglue)


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