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Musings and comments about our common interest

 

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File away these solder peaks!

 

I have been doing some repairs lately, and I have seen some full-nut modules that did not want to work. In the past, I have always classified them as defective and go with another. 

However, this time it was a CX module. This are far rarer and very expensive to get. What's more, I saw it working on-and-off before the repair. (It was a lower post repair), so it should work - but it was not working in the original repaired calculator. Others were working, thoug, and I also managed to make work the CX module on another not repaired body. What could be the problem?

Here is a picture of the lower post repair piece:

test_-_24

I have designed a couple of pads on the left and right of the screw posts to allow for more surface to "glue" onto the keyboard circuit. In principle this surface does not collide with any part of the circuit. In practice, it does: there are some solder points that are a little bit too high - and these press onto the pads and avoid a good contact with the zebra. I have discovered that last week and filing them away has allowed me to "save" this CX circuit - and probably many others goign forward.

The ones to file are the ones at the right and left of the connectors, and sometimes also the ones between both connector lines.

IMG_2379

This may also happen on some cases with non-repaired units when using the zebras over the old support: I see the marks of the solder points on the surface of the film connecting the two parts of the zebra. 

I am updating also the book with these comments.

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Glue for HP41 repairs

In our book we insist on using E6000 glue. This product has been stopped and replaced by the E6000+. The reason for the change is a legal (safety-based) one: there are components and odours that may be hazardous to our health in the old mix. (You can find some in Ebay still - go grab it while it lasts.)

Unfortunately, the E6000+ does not work for our application. I have used it for a low post repair and for a glued battery assembly and it does not hold for too long. In the low post repair, it is enough to impede proper working. The glued batttery assembly did not allow for very tight screwing. The material is too flexible and not adhesive enough for the material we are using. Even if I am too repetitive: E6000+ DOES NOT WORK WELL FOR OUR APPLICATIONS!!

We have heard a lot of good things about the epoxy 2-component glues, and we re testing, but the challenge with these is that you need to do a previous preparation of the glue, by mixing both components and applying the paste onto the parts. I have run some tests this holidays and I am waiting for the glue to cure to make some strenght tests. I will report once I have tested the samples thoroughy. Again, it is a pain compared with the plain E6000 !

 

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HP vintage calculators prices in Europe

 

I wanted to discuss briefly the current price situation for old calculators in Europe. I don't know if this situation is temporary or it will just increase over time. 

We all know that calculator prices have been increasing during the last 2-3 years. I just did not realized how much. 

We do repairs for our customers, and for the HP41 family 90% of the repairs are quite easy and straightforward with our tools and parts. However, something that still requires an original part is when the screen is defective. It may be the LCD, or -more frequently- the display drivers. In these cases, the screen does not show anything or it shows the screen only when pressing a key. According to the service manuals, you need to change the screen then. Your otherwise perfect calculation cannot work unless you find another screen from a donor calculator. (apart from the difference between half-nut and full-nut calculators, the full-nut displays are largelly compatible with each other, save for a little capacitor if you're to use one of the very ealry screen with a later calculator processor)

So, we are always looking for calculators to act as donors. And for that purpose, it is better to find a defective calculator (if it were working well, why use it as donor? you just use it!!)

When I found a lot of 3 defective calculators in eBay Germany, I said "Perfect! I have most likely a couple of screens to repair and maybe other spares too). Be aware that these calculators had already been stripped of all port covers (which are the easiest and nices spare you can get from a defective calculator), so I said "OK - I can offer 150€ tops: two of them are C (for which I have already many processors) and there is only just one CV - for which the processor has a little market value. Then the interesting part are the screens! Let's assume (since these are sold as defective, never forget), that 2 of them are fine, the other really defective. I would be paying 150€ for 2 screens and a CV processor. One of the bodies is tall keys, also - that may have a slighllty higher value. I have plente of bodies without screen, so the body in itself has no value to me (unless it is tall keys, of course). So I bid 150€.

You have here below the results of the bid: 330€! This is crazy! This makes buying an old calculator in Europe (seems that the US is somewhat different and cheaper) totally crazy and you really need to repair your own calculator. The secopnd thing is that we need to say goodbye to calculators that have defective screens - it is just not economical to buy defective calcs for spares, at the price of roughly 100€ per screen (not counting the work of unsoldering and soldering back in the calculation that is being repaired). A pity!

Captura_de_Pantalla_2022-06-23_a_las_19.59.04

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HP Repair book

hprepairbig

Finally it is here!! 133 pages of our repair experiences and methods. Thanks also to the help and advices of Ignacio Sánchez, who suggested many of the repair methods and helped testing them.

You can click on the link below:

HP Repair book in amazon

It is also available on all amazon country sites.

Here is the chapter list:

1. The HP41C family of calculators
Some History
Special features
Serial number and places of production
Peripherals
The HP-IL loop
2. Identify your HP41
C, CV and CX
Full nut and half nut
Tall keys and normal keys
Screen revisions
Special models
3. Tools and Parts
Tools - Required
Tools – nice to have but not required
Contact enhancers
Glues
Conductive inks
Cleaning
Documentation
Other tools
Spare Parts – replacement parts
4. Modes of Failure (or typical problems in HP41c Calculators)
Types of failures
5. Opening and Closing the calculator
Opening
Closing
6. Battery and ports module replacement
7. Zebra replacement
Installation instructions
8. Broken lower post repair
Material needed
Use longer screws.
Cyanoacrylate over the inner part of the post.
Broken post repair
9. Upper Post repair
10. Broken screw head supports
Instructions: first method: back repair piece.
Alternative Method: integral piece.
10. Corroded Circuit Traces
11. Screen Problems
Dirty screen
Screen repair
Damaged Screen Protection
12. Damaged Keyboard
13. Calculator Testing
Test with a Service Module (C or CV/CX)
HP41c
HP41cv/cx
Test without Service module
14. New: CL module installation
15. Peripheral repairs and other items.
Hp 82104A Card Reader
Vinyl Case
Missing port covers
Battery holder
16. Conclusion
Aknowledgements
Appendix 1: The Calculator Store Spare Parts
Appendix 2:HP41C List of parts
Appendix 3: Full-nut circuits
Appendix 4: list of software modules
References and interesting websites.
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