HP 41 Repair for inexperienced owner

[dbhp67]

Hi,

I recently bought an inexpensive non working HP41CV which is in good cosmetic condition. I have done some research and had a look at the repairing book that is available. However I could do with some help in diagnosing what may be wrong with it.

So far I have:
1. Disassembled it. I have then checked the batteries are making a connection to the correct contact on the power connector. From memory I get 2x1.5V on line 3 and another 2x1.5v on one of the middle lines. So i am confident the battery is providing power to the main board.

2. I have checked for continuity wherever I could see any corrosion - there isn’t much, and there is a circuit working in each case.

3. Is there anything else that might be a common failure that I can check with a multimeter?

I have not unscrewed the nut to check the Zebra, but just looking at it it seems very secure. I could try spraying some contact cleaner in there if that might help.

Does anyone have any suggestions as to how best to diagnose a fault, then i can replace whatever i might need....

Many thanks in advance
DB

[aurelio]

(03-04-2021 02:36 PM)dbhp67 Wrote:  Hi,

I recently bought an inexpensive non working HP41CV which is in good cosmetic condition. I have done some research and had a look at the repairing book that is available. However I could do with some help in diagnosing what may be wrong with it.

So far I have:
1. Disassembled it. I have then checked the batteries are making a connection to the correct contact on the power connector. From memory I get 2x1.5V on line 3 and another 2x1.5v on one of the middle lines. So i am confident the battery is providing power to the main board.

2. I have checked for continuity wherever I could see any corrosion - there isn’t much, and there is a circuit working in each case.

3. Is there anything else that might be a common failure that I can check with a multimeter?

I have not unscrewed the nut to check the Zebra, but just looking at it it seems very secure. I could try spraying some contact cleaner in there if that might help.

Does anyone have any suggestions as to how best to diagnose a fault, then i can replace whatever i might need....

Many thanks in advance
DB

Hi DB, if the posts are in a good shape I' would unscrew the nuts in way to check better, sometimes it's possible to find a patina between the zebra and the keyboard/CPU contacts .
But, for better understanding you don't get any sign of life from the calculator?

[AndiGer]

Must be a very early version CV as it has the nuts that hold the mainboard. Never saw that on a CV though.

[mfleming]

(03-04-2021 07:15 PM)AndiGer Wrote:  Must be a very early version CV as it has the nuts that hold the mainboard. Never saw that on a CV though.

I have a single such calc, pretty sure a CV, and it used the gold wire loop style zebra. Relaxation of the core from years of compression may have allowed one or more loops to part from their contacts causing a disconnect of power or signal. The nuts could be loosened a bit, allowed to sit overnight, then retightened after giving the CPU board a bit of a wiggle. Failing that, time to disassemble!

[dbhp67]

    Hi,

Here is a picture of the nuts. Do you mean unscrewing these and maybe spraying some contact cleaner in there?

From the responses I assume it is very unlikely that a chip will be damaged.

Answer to the earlier question : Yes, there is no response whatever from the calculator at the moment. I have a basic ability to check circuits and do a visual inspection and a clean.

Thanks

DB

[aurelio]

(03-05-2021 10:49 AM)dbhp67 Wrote:  Hi,

Here is a picture of the nuts. Do you mean unscrewing these and maybe spraying some contact cleaner in there?

From the responses I assume it is very unlikely that a chip will be damaged.

Answer to the earlier question : Yes, there is no response whatever from the calculator at the moment. I have a basic ability to check circuits and do a visual inspection and a clean.

Thanks

DB

DB, it does not power up as I understand.

looking at your picture it seems definively a CV board

@AndiGer I also thought that nuts were only on the 41c, but if you look please at the CV board shown on Diego's site, here if I'm not wrong in that picture I see traces around the holes which could be left by nuts

DB remove the nuts please and check maybe there's any more dirty or corrosion ... do not spray anything, just clean deeply with isopropyl alcohol (or water and vinegar) and verify the continuity of the circuits, and the conditions of the zebra connector.
I see still green on the PCB, in the right down corner, hope that when you will remove the mainboard you will not find a surprise

[AndiGer]

I'm almost ever scared to open the nuts because they are screwed to the posts - and as we all know the post break often - also on calculators when they get dropped or opened.
So I would suggest to DB in a first step to follow Mark's advice.

Edit: @Aurelio: Thank you for the hint to Diego's pictures. Really looks as if there are traces from the nuts.

[dbhp67]

(03-05-2021 02:05 AM)mfleming Wrote:  

(03-04-2021 07:15 PM)AndiGer Wrote:  Must be a very early version CV as it has the nuts that hold the mainboard. Never saw that on a CV though.

I have a single such calc, pretty sure a CV, and it used the gold wire loop style zebra. Relaxation of the core from years of compression may have allowed one or more loops to part from their contacts causing a disconnect of power or signal. The nuts could be loosened a bit, allowed to sit overnight, then retightened after giving the CPU board a bit of a wiggle. Failing that, time to disassemble!

OK, so tomorrow I will carefully loosen the two nuts and leave it. Is there anything that you can spray on the posts to reduce the chance of damaging the post? Small amount of WD40 maybe? What happens if the post breaks. Can that be repaired / is there a spare part available? At the end of the day the calculator is not working so things can only go one way! ? I will report back!

[mfleming]

Common opinion seems to be that WD40 is not good for this sort of aged plastic. If you have DeOxIT on hand that might serve as a lubricant. A drop of isopropyl alcohol might serve the same purpose. Use of a socket tool would be far better than pliers since it would minimize side forces on the post that could lead to cracks. If resistance seems too great, loosen and tighten to break any adhesive force. In the end you just have to trust to your own feel as as to when the resistance is too great to overcome. The Calculator Store in Spain does have some repair parts, but maybe not for this lower post arrangement.

[dhe]

How's the repair going?