HP41 Cleaning Advice


I have 2 HP41's (Fullnut CV's), one with some dust,and what looks like paper or cotton fibres, behind the screen cover/lens, and the other has a sticky "PRGM" key.
I would love to send these to say Randy at FixThatCalc, but as I live in South Africa, the shipping costs would be prohibitive. So I need some advice.
I can get access to an ultrasonic cleaning bath, but have a few questions:

1. Can I just use water in the bath, or should some other cleaning solution be used?
2. How long should the calculator remain in the bath for?
3. What frequency should be used?
4. Should the LCD be kept out of the bath (I assume it should)?

Second issue (screen dirt):
1. Is it very difficult or dangerous (in a destructive meaning) to remove the LCD screen and clean out the dirt and dust behind?
2. Any precautions or advice in carrying out this task?

I would appreciate any advice from forum members.



I never 'bathed' any of my calculators while assembled, instead when needed I disassembled them as much as I could and cleaned the parts accordingly. Plastic parts I cleaned with water and small amounts of neutral detergent. In some parts, without painted labels, I try some water diluted bleach to remove watermarks or any residual that would not leave with detergent.

Components and boards I rarely clean, just remove any dirtiness with small handbrushes. If necessary I use metal polisher for contact surfaces, and some smeared micro oil to protect the overall circuits. Because circuitry is (almost) always enclosed inside the device case, they do not need bath.

The coconut LCD is not hard to remove. See some pictures here, starting with this one and ahead. Once removed it is easy to clean the space between the LCD and the transparent protective window.

(added) Precautions are standard for ESD sensitive devices: all available ESD preventing protection (grounded conductive surface workbench, grounded conductive wrist ring, etc.) and a lot of care when handling the calculator. If you believe you need extra physical force, consider that the procedure is probably wrong.


Luiz (Brazil)

Edited: 8 Apr 2012, 3:09 p.m.


Thank you Luiz, these are excellent photographs and will give me the confidence to proceed.
The reason I asked about the ultrasonic bath, is to clean inside all the key domes. I have cleaned the PRGM key with success, but it takes a long time with the fine wire bristles. To do all the keys seems quite a job.
As always thanks for your advice


Try compressed air for the dust removal behind the screen. I used a can with a thin pipe straw that came with it. Just apply gently by the upper edge from behind. Just be careful not to use too strong air.


For one problematic key, I would not resort to ultrasonic cleaning, you risk discoloration of the plastic, even with water. Stick with the wire brush technique.

Removing LCD assemblies: once unsoldered and all connections are free, flip it over and allow gravity to help remove the assembly. Do not try to force it out, just turn it over and it will fall out with a little tap on the front side. DO NOT attempt to remove without first ensuring all connections are free moving, otherwise you will almost certainly tear traces off of the keyboard assembly.

The edges of the polarizers (the part that sits above the glass and is smaller the the display area) are sticky which is why they hold the dirt. Use a cotton swab and isopropyl alcohol to remove. Be very, very careful with the polarizer, they are very soft and scratch at the slightest provocation. You do not need to remove the top and bottom clips that hold the LCD against the driver module nor would I recommend you do so. It would be too much stress on the LCD and you risk fracturing the glass to glass seal of the LCD and ending up with the "creeping crud" where the liquid crystal material leaks out at the edges and you end up with permanent black areas.


Thanks to everyone for the advice. Truly a great bunch of people, always ready to impart years of experience to help.
Thanks again

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