Dead 41C?

[Jean-Michel]

Hello all

It seems that my ’79 HP-41C passed away last night… I was unable to switch it on this morning. I tested the batteries and they all show 1,47 V or so.
I scrached the terminals to remove corrosion (there was not, but who knows?)
I tested the BEEP in case the screen was the only one faulty, with no success.
Before doing anything bad, could you please share your advices?
Yes, I know, this might be detailed somewhere in the forum, but, to be honest, I must confess I'm too lazy to look for it.
Should I leave it overnight with no batteries?
I have other HPs handy, but as many of you, I have a special relationship with this model.
Help much appreciated. Many thanks advanced.

JM.

[d b]

See this from the old forum.
It's originally from page 63 of Extend You HP-41 by Dr. W Mier Jedrzejowicz
Thanks to Steve for typing it out there and leaving additional notes.

My note on #11's "short the contacts with foil and leave for a long time": according to Corvallis, a long time is 6 months. That is a long time but it worked for me and is why I got my second 41.

[quantalume]

If the suggestions that Den linked to don't work, then I suspect that some of the internal connections may have become interrupted due to a broken screw post. One thing you can try in this case is to set the machine down on a desk and press firmly in all four corners while pressing the ON switch. Given the vintage of your machine, it may have nuts holding the CPU board in place, and in this case the four-corner method may not work. However, it's very rare that a 41C cannot be made to work again, given the required patience and skill.

[Geoff Quickfall]

Modify that old post with the following:

DO NOT do the drop method.
DO NOT do the twist method.

DO check that the screws are tight, but, DO NOT over tighten. Loosen them then tighten until they JUST sinch up.

So do the following before opening up testing at each step:

-Check screws for tightness. DO NOT over tighten. Are any stripped? Are any loose and will not tighten? Do the two shells look or feel loose, Check for gap between the two shells and the spacer.
-Two finger salute: ON and CLEAR memory reset.
-Remove batteries and short the far left to the far right battery contacts.
-Remove batteries and replace in opposite polarity. Place in calculator, turn on and count to five then turn off. Remove pack, correct polarity. Reinstall and check.
-Remove batteries and leave a few days.

DO NOT THROW OUT!

Next will require surgery:

-Separate the shells (four screws under the foot pads).
-inspect the screw posts, any cracks, are they broken at the base?
-Foot pads are anti static impregnated with conductive material.
-Any visible corrosion?
-There are two contact groupings on the full nut keyboard. Clean the keyboard PCA contact points with lint free cloth and anhydrous alcohol (or isopropanol 99%). Do not substitute with a harsher solvent.
-Clean the battery/module contact points in the same manner.
-Inspect the battery/module block. There is a foam strip which pushes the contact on the battery/module block against the keyboard PCA. Is it flattened? Pinch the sides of it to get it to push the contact point higher.
-Clean the contact block (wire wrap or elastomer assembly).

Do all the above then reassemble.

There is a capacitor in the calc down by the old battery ball contacts on the keyboard PCA. It is electrolytic and MAY need replacing. Last resort would be to replace it as it may have dried up internally.

Let us know how it goes!

Geoff


Don!

Cell phone is for work and on days off I never carry it as I don't want to work! So I did not get your message until going to London Saturday. The problem has been solved via the committee.

Cheers, Geoff.

P.S. Quanta lumes suggestion is excellent, before the surgery follow his press suggestion. The intent is to see if the compression force at all four corners of the calc will revive it. If the screws are tight and this does work it indicates the contact mechanism of the battery/module block or the wire wrap or elastomer assembly at the lower contact point are not fully functional.

[Jean-Michel]

Thank you all three for your prompt and detailed replies!

I will print them and plan some free time to cure my old lady. I tried to firmly press the shells one onto the other this morning, with no success, but I did it only once and probably not firmly enough and also not at the right place, so I will try again better. I was at work with not much free time, so I picked up my 33C to do my computations and leaved the problem aside.

I will keep you informed of further steps and come back to you if needed.
Geoff, don't be afraid, I won't throw it out, even if my skills are not good enough to make it work again! These are venerable pieces of calculators.
Cheers.

JM.

[wojtek]

(02-17-2016 01:53 PM)Jean-Michel Wrote:  ................... I tested the batteries and they all show 1,47 V or so.

One more idea: change the batteries, or check the ones you used for the current they can provide. Correct voltage doesn't mean that the batteries are OK for sure. I still have a set of completely used 4 pieces of N-size batteries of 1980's (Hitachi/Maxell), valid through 1992, which have 1.49V but the current they give is less than 1mA. As they have no traces of any leakage I stiil keep them as a curiosity.

[Brad Barton]

(02-18-2016 12:27 AM)wojtek Wrote:  One more idea: change the batteries, or check the ones you used for the current they can provide. Correct voltage doesn't mean that the batteries are OK for sure. I still have a set of completely used 4 pieces of N-size batteries of 1980's (Hitachi/Maxell), valid through 1992, which have 1.49V but the current they give is less than 1mA. As they have no traces of any leakage I stiil keep them as a curiosity.

When testing (non-rechargeable) batteries it's a good practice to short the ends together for a few seconds with a paper clip or small wire. This allows you to discharge the 'surface charge' that even a spent battery can build up over time. Careful, the paper clip can get hot, so only hold it for a few seconds. Then test the voltage. A good battery will recover full voltage very quickly.

[Jean-Michel]

Hello

As promised, here you are some news.
I tested what Brad suggested to me, and batteries are good. Surprisingly for such an old device, none of the screw posts is broken. I follow your advice and did not over tighten, Geoff.
Having a closer look at it, it appears that the problem was only caused by a loss of electrical contact at one of the four terminals. The thin copper sheet is worn at the top of the dome, at the location where the battery applies the pressure.
Since I have not much skills in soldering such tiny parts, and probably also not the right tool (my soldering iron seems to big, even if already small), and also I did not want to damage anything, I ended up with a simpler quick and dirty solution: I cut and folded twice a small sheet of aluminum (for cooking use) that I just put between the faulty terminal of the calculator and the battery terminal.
This works just fine, but I would be pleased with a more definitive solution, less fragile. I would also know if aluminum is conductive enough or if copper is better, just in order to have the same current drain at each of the four terminals.
What would you suggest to me at this point?
Many thanks advanced and kind regards.

JM

[Dave Frederickson]

(02-22-2016 08:25 PM)Jean-Michel Wrote:  What would you suggest to me at this point?

[Massimo Gnerucci]

Diego's new flexible I/O contacts are the best solution.
Alternatively you can try with conductive paint. I did on one of my 41s and it still goes strong.

[cruff]

(02-22-2016 08:25 PM)Jean-Michel Wrote:  I cut and folded twice a small sheet of aluminum (for cooking use) that I just put between the faulty terminal of the calculator and the battery terminal.
...
What would you suggest to me at this point?

Two dissimilar metals/alloys in contact, with an electrical potential across them, will cause further corrosion. Thus, you should consider replacing the I/O flex board as suggested.

[aj04062]

(02-23-2016 12:20 AM)cruff Wrote:  

(02-22-2016 08:25 PM)Jean-Michel Wrote:  I cut and folded twice a small sheet of aluminum (for cooking use) that I just put between the faulty terminal of the calculator and the battery terminal.
...
What would you suggest to me at this point?

Two dissimilar metals/alloys in contact, with an electrical potential across them, will cause further corrosion. Thus, you should consider replacing the I/O flex board as suggested.

If it is either one of the two center contacts, these just provide a contact connection for the batteries in the tray. I've used some sticky back copper tape to fashion a contact that can be applied over the top of the two center contacts.

No dissimilar metal problems!

[Jean-Michel]

Hello all, and especially Massimo

Thanks for your tips. I apllied conductive paints on the faulty terminal and it works nicely!
Kind regards.

[Massimo Gnerucci]

(03-03-2016 07:40 AM)Jean-Michel Wrote:  Hello all, and especially Massimo

Thanks for your tips. I apllied conductive paints on the faulty terminal and it works nicely!
Kind regards.

Glad it worked.
Another 41 still alive and kicking! :)