HP41c Repair

HP 41C Repair

HP 41C Repair
The HP 41c family of calculators started being produced at the end of 1979 and lasted in its last versions until 1991. Such production time span attests its quality and advantages for the work of engineers and scientists. Many of you had a HP41c at its day, or lusted for one and you've given yourself that gift. But one day you pick it up from the drawer, or it falls to the ground, and it doesn't work anymore. What do you do?
Repair it!
We are fanatics of the HP calculators, and the HP41c occupies a warm place in our heart. We have repaired many of them, and we think that we have seen most of the problems that these machines have. We do not claim to have found the solution for every problem, but we have for most of them. 
The first HP calculators were very solid and well designed. The body was independent of the circuits, and the screws that secured the circuit were not required to hold the machine together too. This resulted in more robust calculators. The HP41c, with all its technical advances, was not as well designed as the calculators that preceded it (with the exception of the Spice series, which was a true desing flop). We have identified several weaknesses that appear again and again, and we have found solutions for them. Click on each problem to go to the respective page.
How to determine what is your problem? Beware - you may have to disassemble your calculator!
Corrosion on the contacts is very easy to spot. You can see the battery contacts corroded. It is usually the leftmost contact which gets corroded first. This is the lowest potential point ("-" contact)
Broken upper back case screw head supports: you can see both halves of the case are loose in the upper part of the calculator. This impedes power transfer from the battery to the circuit. If you take the upper rubber feet out with a small flat screwdriver, taking care of taking the adhesive sheet with it, you see the screws below. You will be able to see that they are "free" in this case. If they are not free, the the problem may be the broken upper repair posts - and you'll need to disassemble the calculator to see it.
Broken lower screw posts: the lower part of the calculator seems loose, and it may happen that it works when applying pressure to the lower part of the calculator keyboard (around keys 1, 2 and 3)
Corroded or broken zebra contacts: you can only see it if you open the calculator. Indicators of this problem may be missing digits or segments in the screen, or the calculator not working.
Corroded circuit paths: you can only see it if you open the calculator. Usually happens with battery contact corrosion - never comes alone!
Damaged screen: in all cases disassembly is required.
- black spots: seen in the screen. You can only change the screen (soldering required!)
- not all segments lit: it can be the connections to the screen, the lower zebra corroded, the lower screw posts broken, etc.
Dirty screen: you can try with pressured air through the side openings, and if it doesn't work you will have to unsolder the screen.
Damaged plastic protection: complicated! sometimes the damaged plastic protection is easy to take off the machine; you need to disassemble and unsolder the screen; if it doesn't separate easily, we have not found yet a way to repair it.

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New Zebra connector for HP41C repair

Product no.: Zebra PCB

This piece is for repair of HP41c full nut calculator, substituting the damaged or corroded zebra connector that links the main board with the processor circuit. New design.

16.00 *
In stock

Spacer set for repairing old HP41c

Product no.: SpacerSet

Set of 8 pairs of spacers for nut-screwed full-nut HP41c calculators. Substitutes the nuts that are screwed on the lower posts to secure the circuit, 

10.00 *
In stock

lower post long screw - inox

Product no.: lowerscrew

Two long screw for the lower screw posts of HP41c calculators

1.00 / 2 piece(s) *
In stock

lower post long screw - black pair

Product no.: lowerscrewblack

Two long screw for the lower screw posts of HP41c calculators - black

4.00 / 2 piece(s) *
In stock

New Set of 4 screw for HP41 - inox

Product no.: Screwset

Two long screw for the lower screw posts of HP41c calculators + two long screws for upper posts.

3.00 / 4 piece(s) *
In stock

4 x Piece for repair of back case of HP41C

Product no.: brokenback4

4 pieces for repairing HP41c back cases.

This piece is for repair of HP41c back halves, specifically the support of the upper screw heads that is often damaged, and very difficult to repair in a lasting way.


50.00 *
Old price 72.00 €
In stock

New HP41c Lower Post Repair Kit

Product no.: Lower Post Repair Kit

Set of pieces needed to repair successfully the lower posts of HP41C, 41CV and 41CX full nut calculators, including zebra connectors, lower post part, and keyboard support for clothes' pegs to protect the keyboard

60.00 *
Old price 70.00 €

HP41c battery holder spring

Product no.: Spring

Stainless steel 304 springs for HP41C battery holder

3.00 *
In stock

Piece for repair of back case of HP41C

Product no.: brokenback

1 Piece for repairing HP41c back cases.

This piece is for repair of HP41c back halves, specifically the support of the upper screw heads that is often damaged, and very difficult to repair in a lasting way.


14.00 *
In stock

New Lower Post Repair part

Product no.: Lowpostrepair

Piece to repair HP41c full nut series lower screw posts

25.00 *
In stock

New Upper Post Repair part

Product no.: UpperPostRepair

Piece to repair HP41c series upper screw posts (tested with both fullnut and halfnut versions)

25.00 *
In stock

Keyboard support for repairs

Product no.: keyboard support

Piece required for the lower post repair of HP41c calculators.

25.00 *

New zebra connector holder

Product no.: zebraholder

Zebra Holder to keep the elastomeric zebra connectors in the contacts between main board and processor circuit in the HP41c calculator family, full nut versions.

12.00 *
In stock

Repaired HP41c back side

Product no.: HP41Cback

Repaired back side of HP41c. It can be used in case the original backside has the screw supports broken.

40.00 *
In stock
* Prices include VAT

Corroded Battery contacts

Instructions for battery and ports module


Broken upper back case screw head supports

Instructions to repair the upper back case screw head support.

Broken upper screw posts

Upper post repair

Broken lower screw posts

Broken Lower Screw Post Repair

Corroded or broken zebra contacts

  • Open the calculator


Corroded circuit paths

Under construction

Damaged screen - black spots

If there are black spots in the LCD, the only solution is to change the screen. These are not produced anymore, so you will need to find a donor HP41c.

Damaged screen - not all segments light on

When the screen does not allow all segments to be seen, it may be one of several faults:

- Bad connections of the lower zebras

- Bad connections of the lightly soldered screen pins

- Bad connection between the LCD and the screen driver

- One of the two screen driving circuits gone bad

We will discuss all cases in the article.

Dirty screen

How to get out of the screen these specs or dirt accumulated over so many years.

Damaged plastic protection

After a lot of time, we have just found a good solution to repair your scratched HP41C screen. There is an abrasive product used to repair watches' plastic screens, called Poliwatch. You can easily get it from Amazon and other sources. 

The method: just apply a little quantity on the scratch, and then rub firmly with a soft cloth. You will get, once cleaned, a bright surface without scratches. Note: after some tests, we have found that the dremel method can overheat the plastic and lead to internal cracks or material deformation. It has to be manual!

Beware: do not try to use this material on crystal - it is so hard that it would not help at all.