HP 41CV Key Issues

[Michael Lopez]

Hi all,

I recently acquired a 41CV which is in excellent cosmetic condition & works fine except for the "." & "Alpha" keys occasionally not registering despite a positive click. All the keys on this calculator feel fine & very similar to the ones on my 41CX which works flawlessly.

The 41CV is a fullnut version where the 41CX is a halfnut.

Just wondering if there is any simple way of cleaning/lubricating the contacts in these keys without pulling the whole calculator apart as it is hardly worth doing when they work 8 out of 10 times?

Many thanks,

Michael

[Geoff Quickfall]

I had the same problem on two restorations. Both had positive clicks but failed to register the key input.

One was the on/off rocker arm similar to you alpha key and the other calculator had 3 of the digit keys not registering. The keyboards were in excellent condition.

Try the following, get an eye dropper and place a drop of water on the offending key. Work the key back and forth numerous times. Blot the water off and then add a drop of alcohol, repeat the key exercise. Let dry and try the keys. I use a lens cleaner bulb blower to force air around the key when drying.

If it does respond, or does not, the next step and with nothing to lose, dis-assemble the calculator; i.e. remove the back case, then remove the PCB and the zebra strip from the keyboard.

During the following, keep the LCD above the level of the liquid.

- Get a tall glass wide enough to accept the keyboard upright.

  Fill with luke warm mildly soapy water to BELOW the level of the

  LCD panel.  Insert the keyboard and let soak.  Agitate the water

  by stirring or by subsequent and repeated removals of the 

  keyboard out of and back into the water.  The intent is to 

  remove any sugar based or sticky water soluble material from the 

  keyboard contacts.

- If you suspect corrosion as indicated by leaky batteries or blue 

  corrosion on some of the contacts then using the same glass,  

  rinse the keyboard in dilute white vinegar.

- I then rinse the keyboard in the glass with water, using the

  same method. 

- Next rinse with alcohol in the same manner.

- Air dry or use a drying box to accelerate the drying proceedure.

  (see photo below)

-Re-assemble and try it out.  

1 The soapy water will remove non conductive oil based, sugar 

  based (coffee spill, sherry!!) as well as particulate   

  contamination.

2 The vinegar will dissolve the corrosion due to outgassing  

  batteries.

3 The water rinse will also remove sugar based contaminants, 

  particulate matter and soap residue.

4 The alcohol removes or mixes with remaining water and will help

  in the drying process

THIS HAIR DRYER HAS A "COLD" SETTING, no heat applied!!!

[Michael Lopez]

Thanks Geoff. I'll try the eye dropper trick first & see how that goes.

Cheers,

Michael

[Michael Lopez]

Done & can confirm Geoff's eye dropper trick works. Thought I would start with an even slightly simpler approach & just added a drop or two of rubbing alcohol to the keys & repeated use with the calculator off then on whilst absorving the excess alcohol with tissue paper.

The "." key improved immediately whilst the "alpha" key took a little longer & I think I got a bit carried away with the amount of alcohol I added as the display went a bit funny for a while (a bit disturbing) but all came good with a bit of forced cool air drying.

Now all keys work fine first time.

Thanks again Geoff.

Cheers,

Michael

[John Mosand]

Shortly after I bought my 48SX in 1991, the following happened:
One morning I came down to the kitchen and found that the cat had tipped over a flower vase, dumping its contents over the calculator. Unfortunately, the water contained an amount of 'growing additive'.
Turning it on resulted in crazy displays, numbers that I never knew existed :-) Keys sticky. I removed the batteries and rinsed it under running tap water, shook it out and left it in the convection oven at its lowest temperature. When I came back from work and replaced the batteries I was pleasantly surprised. Wow, it behaved like normal and has been perfect ever since! (BTW I have changed batteries only once.)
Of course, I don't know if the 41CV and the 48SX are similar in this respect...

[Geoff Quickfall]

in 1986. Flight attendant places a glass of sherry on my table tray and then reaches over to the passenger beside me, knocking over the glass onto the keyboard.

I watched the display act up and die. Of course the sugars in the sherry as well as other compounds completely altered the resistivity and electrical qualities of the circuit.

Rubbing alcohol did not work as a cleaner as it did not dissolve the sugar. I had to resort to a warm water rinse and then the alcohol to aid in drying.

Cheers, Geoff

[Gene Wright]

Hmm...

I was wondering what your class was studying at University to be having a glass of sherry handy.

(former business professor... could not resist)

[Geoff Quickfall]

OOPs

"business class" in an airplane GENE, as opposed to "business class" at University.

;-)

Although I did have beer in my office as a Teaching Assistant at University, would that count!!!

Ha Ha , Geoff

P.S.

Got an email from Joe, have you recieved my registration, second form sent last night.