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HP Forum Archive 11

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HP-41C Dust in the display
Message #1 Posted by Jon on 5 Apr 2003, 3:14 a.m.

I have a working HP-41C thanks to the help I got in this forum (connection problems). Now I see it has dust in the display. It seems a common problem in these calculators. So, may be somebody knows how to remove it.

Thanks in advance


Re: HP-41C Dust in the display
Message #2 Posted by Randy on 5 Apr 2003, 8:42 a.m.,
in response to message #1 by Jon

Canned air will usually blast it out. Never use air from an air compressor, it will always contain moisture and oil. Just direct it in around the top and sides of the lcd. If it's a full-nut, remove the plastic strip along the top of the lcd for better access.

You can fish a strip of paper into the lens area to dislodge stubborn specs. I use a piece of plastic coated paper since it slides easily and holds it's column strength for a while. The paper off the back of an address label works well.

HP-32S DUST IN THE DISPLAY and my 2-bits worth
Message #3 Posted by NH on 5 Apr 2003, 3:42 p.m.,
in response to message #2 by Randy

HEY I have got several HP-32S that I bought around 1990, and those stinkers almost IMMEDIATELY began to accumulate household dust in their display.

Now one guy just said "dont use an air compressor it always contains oil and moisture" and I want to disagree with that. If you happen to have chosen an oil-less air compressor you can get some really nice dry air out of it. I chose oil-less for my garage-shop and have no regrets that the air is always clean & dry. Some of the metal-shop guys chastise me because the air-tools dont get lubricated. Thats what a hand-oil-can is for. Just put some drops right into the inlet of the tool. And about dryness, humidified air loses its moisture under pressure, thats why a puddle of water accumulates in a compressed air tank. Thats why any knowledgeable owner of an air compressor installs an easy-access ball-valve at the bottom and operates it often. Its even a safety issue to reduce the likelihood of a tank rust-through. Meanwhile when the air comes out the gun it is DE-pressurized, it is very dry because its been thru, effectively, a pressurized dehumidification process. The remaining risk is specs of debris in the hose, but the odds are in your favor there wont be much of that. Therefore at my shop, the air compressor is the FIRST THING I would reach for, not the last.

LASTLY, does anybody else have further info about how to clean out a 32S ?? I am not real enthused about the compressed air because it does not solve the real problem. I think you need to get in there and clean it out for real and maybe seal it, IF thats possible, I never tried but wondering if anybody else did (for reasons of house dust).

Although we are supposed to bow down and worship the might HP Calculator Gods, I think they are buffoons in regards to dust getting in the display. I was disappointed even around '92 when the dust in the display was appearing, I mean, '92 was hardly a medieval era, and it was a substandard design to have something so ridiculous as the display get dirty from the inside.

Modern equipment tests for new designs include

(a) test for electro-static-discharge immunity with a spark gun

(b) test for radio-frequency susceptibility or transmissions

(c) test for durability. This is often done by putting the unit in a tumble-dryer with a variety of objects and some house dust and grit. It has to get tumbled awhile and still be useful in the end.

Looks to me like HP didn't do any of that for their supposedly superior modernized "LCD" calculators or I wouldn't be asking about the dust in the display. I'd wager that the red LED HP-34C is more likely to pass the dust-in-the-display test. (NO you cant test mine!)

The 32S - It was supposed to be a low cost unit...
Message #4 Posted by Randy on 5 Apr 2003, 5:27 p.m.,
in response to message #3 by NH

Disagree all you want. Arguments are down the hall, second door on the left.

I seriously doubt the average Joe with an air compressor in the garage went through the same decision tree as you in selecting their unit and accessories.

When it comes to cleaning an expensive, vintage piece of electronic equipment, I defer on the side of safety. Even with clean air and an OSHA safety gun, I think the pressure delivered from a compressor could do some major damage to a calculator. Blow the rubber zebra strips out of place, knock the keyboard discs off center, etc,etc. Not to mention the static potential of air at that speed. Is it worth the downside risk to save $4? Not to mention the fact that a 3/8" diameter air chuck isn't going to get you very close to the fine gaps around the display as well as a 0.090" flexible tube. Use the right tool for the job is my motto.

As for your dusty 32S, it does usually blow out if you stick the flexible tube in the side of the case. Takes a while, but it can be done. You can always check the archives for Paul Brogger's article on how to open a Pioneer, it does make make the job easier if you dare. I suppose you could try to seal the LCD area, would not be too hard to do once the back was off. I would be concerned about condensation once closed though.

The first versions with the double lens unit was pretty quickly changed to eliminate the dust collector. I guess Hp felt it was better to scratch the surface of the LCD than to have dust collect between the two surfaces. I prefer the later version, not because of the dust issue, but because the recessed LCD does not reflect overhead light as badly, making for easier viewing on the desktop.

Opening the case on 32S better ...
Message #5 Posted by Norm on 7 Apr 2003, 12:56 a.m.,
in response to message #4 by Randy

Suggest that rather than get into all the various issues about an air compressor, it might be better to figure out how to open the case on the 32S.

I did try it just now. This air compressor that I have confidence in, it also has 2 connections on it... raw pressure from the tank, and then another that was dropped thru a regulator.

The tank pressure is about 130 psi. I dialed the regulator down to 40 psi and tried it. It really didn't seem to help with the old and dirty-looking display problem on the 32S.

Suggest that probably the best thing would be to open the case up, and clean it manually from the inside out. I'd be interested in starting a chat thread, about how you open the case on a 32S.


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