The Museum of HP Calculators

HP Forum Archive 13

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HP 41C fixes?
Message #1 Posted by Paul Pickett on 16 May 2003, 11:26 a.m.

Thanks for all the responses!

On second thought I'm beginning to think that maybe reviving my 41 to its original glory is the way to go. Can I apply a little 409 to the body and keypad or is 409 a calculator solvent?

I put the card reader on and slipped a card and yuck. It went halfway through and came out gunky. I've browsed the articles forum and I see some instructions on how to repair card readers. My question is could some first-timers tell me how their experience at using these techniques worked? The whole sequence looks a little daunting to me. Is this something "anyone" can do if he follows the instructions?

Also I have some corrosion on the battery contacts. It still works but it's ugly. Is there anything to do besides rub it off?

      
Re: HP 41C fixes?
Message #2 Posted by Randy Sloyer on 16 May 2003, 12:13 p.m.,
in response to message #1 by Paul Pickett

Never use 409. It contains sodium silicate. Etches glass, discolors plastics, especially old black 41's. Mild glass cleaners without additives are best. Don't soak them, spray lightly and invert to allow it work so it does not get into the keyboard.

The hardest part of card reader repair is avoiding loss of the little bits that come out upon disassembly. Take it slow, make notes if you feel the need. Cleaning the goo just takes time. It must be spotless with no stickiness remaining or you'll have problems. If you run into trouble, don't panic, put it aside and ask questions. Re-visit with a clear head and it will go back together.

Best to clean the battery holder out of the calculator in a dilute solution of vinegar. Follow up with a solution of water and baking soda to neutralize. It should remove the green without scraping. You may have to resort to a copper foil patch if the original gold/copper is gone.

      
Re: HP 41C fixes?
Message #3 Posted by Ellis Easley on 16 May 2003, 12:29 p.m.,
in response to message #1 by Paul Pickett

On the battery contacts, this recent thread mentioned two ways to repair serious corrosion:

http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/forum.cgi?read=33949

I haven't rebuilt a 41 card reader yet but I have done a 97 and a 67 which have a similar mechanism, although I understand the 41 card reader enclosure is a little tricky to open. Actually cleaning the goo was not difficult and you need to get rid of all of it. I used a lot of Q-Tips and 91% isopropyl alcohol. I used silicone rubber tubing to replace the wheel and it was very easy. I found the tubing at an RC model shop, they didn't have the sizes marked, just large and small, so I bought some of both and one was right. The pieces I used are not as concentric as they might be (machines "chug" a little) and since I have several feet of tubing, I'm going to select some more concentric bits some time and put them on.

I wouldn't use 409 on my calculators. I don't know what's in it or other cleaners that are intended to be used without rinsing. I use dishwashing soap solution on a clean sponge squeezed almost dry. For the keyboard, I use a brush with short bristles (~1/2") bigger in area than the calculator (~5" X 4") and load it with just soap suds - just damp with water and a little suds. I hold the brush with bristles up and lower the keyboard onto it and move it in small circles. Then keeping the keyboard facing down (laying it on a towel) I rinse the brush, shake out all the water I can, and use it to rinse the keyboard in a similar manner - I do this two or three times. Then, still holding the keyboard facing down, I use a vacuum cleaner with the small brush attachment (cleaned for the purpose!) to dry the keyboard and remove any water, suds, or loosened crud.

      
Re: HP 41C fixes?
Message #4 Posted by David Smith on 16 May 2003, 4:40 p.m.,
in response to message #1 by Paul Pickett

I used to use Novus plastic cleaner on my keyboards, but ran out. I also use Windex. Spray it on (I dont worry too much about it getting under the keys... HP keyboards are fairly well sealed against minor spills), clean with a soft toothbrush, wipe off with small wads of paper towels (change often, like between each row of keys). Blow keyboard with canned air, wipe off liquid blown out of keys. Repeat. If you can find it, do a final cleaning with a lens cleaner called ROR (residual oil remover).

            
Re: HP 41C fixes?
Message #5 Posted by Ellis Easley on 17 May 2003, 9:31 a.m.,
in response to message #4 by David Smith

I got a pamphlet about Novus plastic care products at the plastic supply house I went to recently. It is a system - cleaners and polishes. Are you talking about "Novus No. 1 Plastic Clean and Shine"? The place I went to is called Regal, it is on the east loop in Fort Worth and they have a place in Dallas on Merrell Rd. (also San Antonio, Austin and Houston, and that's just the southern region!) They have a $25 minimum but I might go back because they have a scrap pile of plastic sheet odds and ends they sell for 75 a pound.

                  
Re: HP 41C fixes?
Message #6 Posted by David Smith on 18 May 2003, 9:24 p.m.,
in response to message #5 by Ellis Easley

Yes, that's the stuff. I usually buy it from a place on Ebay that sells it for cleaning up pinball games. They also have a coarse and fine plastic scratch remover good for cleaning LED/LCD windows... but I don't like it becuase it is hard to get it out of the corners of the window.

      
Re: HP 41C fixes?
Message #7 Posted by Paul Brogger on 16 May 2003, 5:40 p.m.,
in response to message #1 by Paul Pickett

I just did my -97's card reader for the first time a few weeks ago. It all went pretty smoothly, but I had to do it twice -- the first time thru, I left some ArmorAll on the read/write head, and maybe that was enough to keep it from working. (It passed the cards fine, but gave an Error with each read attempt.)

Also, one of the references suggested I lightly sand the ends of the "little gold fingers" (switch contacts) inside. So, somewhere between a cleaner read/write head and cleaner switch contacts, the second time worked like a champ.

            
Re: HP 41C fixes?
Message #8 Posted by Ellis Easley on 17 May 2003, 9:17 a.m.,
in response to message #7 by Paul Brogger

I had to clean the fingers too but I used the famous "Pink Pearl" pencil eraser that is frequently recommended for cleaning the gold plated card edges on option boards.

                  
Thanks to everyone!
Message #9 Posted by Paul Pickett on 19 May 2003, 4:40 p.m.,
in response to message #8 by Ellis Easley

My 41C is looking and feeling like new again! And with no etching from 409!

I've assembled my tools for the card reader and will do that soon.

                        
Re: Thanks to everyone!
Message #10 Posted by Patrick on 19 May 2003, 4:59 p.m.,
in response to message #9 by Paul Pickett

With a name like yours, Paul, why aren't you collecting slide rules??

                              
Re: Thanks to everyone!
Message #11 Posted by Paul Pickett on 19 May 2003, 6:23 p.m.,
in response to message #10 by Patrick

I started to ask how Paul was a good name for collecting slide rules but then I got it! Obviously I'm hanging out with a sophisticated crowd here and I'm going to have to think before I reply to anything!

If I had been born about five years earlier I might have used a slide rule. Perhaps even one of those famous PAUL slide rules! :-)

                        
Re: Thanks to everyone!
Message #12 Posted by Ellis Easley on 19 May 2003, 5:26 p.m.,
in response to message #9 by Paul Pickett

Congratulations! Ain't it great?

                        
Re: Tools for Card Reader Repair
Message #13 Posted by Paul Brogger on 19 May 2003, 8:02 p.m.,
in response to message #9 by Paul Pickett

I should have mentioned, some of the cross-head screws on my '97 card reader were surprisingly tight. I had to exert more force than I would have expected to keep the screwdriver in the slots and get enough torque to loosen them.

So, Get yourself a good array of quality screwdrivers with sizeable handles. I found the regular jeweller's screwdrivers' handles were way too small for the kind of pushing and twisting that was required. (And take this all slow -- the kind of pushing I'm talking about was performed with the card reader "body" in my left hand -- you don't want to be stressing other parts unnecessarily, but neither do you want to punch a driver through your palm . . . )

Also, I never quite understood the pinch roller hub. It's kind of a hard nylon axle with a screwdriver slot at one end. It's supposed to help adjust the pressure on the pinch roller, but I couldn't come up with a theory as to how. (Maybe some knowledgeable person could hold forth on this topic?)

                              
Re: Tools for Card Reader Repair
Message #14 Posted by Katie on 20 May 2003, 11:03 a.m.,
in response to message #13 by Paul Brogger

The white nylon axle that the pinch roller rides on is actually call the "eccentric cam". Take a close look at it and you'll see that it's not quite symmetric. By turning it (that's why the screwdriver slot is there) you can very slightly vary the distance between the pinch roller and the head.

                                    
Great stuff! Thanks!
Message #15 Posted by Paul Pickett on 20 May 2003, 3:41 p.m.,
in response to message #14 by Katie

I'm ALMOST ready to attack this.I'm going to get some better screwdrivers tonight.


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