The Museum of HP Calculators

HP Forum Archive 14

[ Return to Index | Top of Index ]

Cleaning an hp48 keypad
Message #1 Posted by andy on 24 May 2004, 3:31 p.m.

I have an hp48s which appears to have had a coke spilled on it. Fortunately the battery compartment looks to have been spared but the keypad has several keys which do not operate.

I noticed a previous posting which advocated soaking a 32s in distilled water overnight, however, I've seen the inside of a 48 and there are electrolytic capacitors on the PCB.

Any suggestions?

Thanks,

Andy

      
Re: Cleaning an hp48 keypad
Message #2 Posted by Randy on 24 May 2004, 7:54 p.m.,
in response to message #1 by andy

Distilled water will not bother them, 15 minutes max each rinse is all you need. There is only one electrolytic, the 1000uf battery bypass/backup cap.

Warm water is better (95-100f max. Remove the battery and port covers, soak, take out, shake out water, push all the buttons, resubmerge in same water then repeat with fresh water three times. Shake out well, leave to dry in a warm place for two days. A fan blowing on it helps.

Pop usually washes out okay. You need the warm water to dissolve the sugar. Pushing the buttons alot while submerged helps drive the crud out of the keydomes.

If the batteries where left in and it was really, really saturated with liquid it could be toast as the ON switch traces will open due to electrolysis. If it's dead after it's dry, that's usually the reason.

Edited: 24 May 2004, 7:58 p.m.

            
Re: Cleaning an hp48 keypad
Message #3 Posted by andy on 24 May 2004, 10:43 p.m.,
in response to message #2 by Randy

Thanks for the advice. Its not dead yet...it turns on but ~40% of the keys don't work (some work some of the time). Actually, to turn it on I have to hit on-C (the system halt sequence). The on key by itself won't turn it on. Hopefully that's not a portent of doom.

I'm going to try the distilled water. One more question:

Will distilled water damage the display? Should I only submerge the keypad section?

Thanks again,

Andy

                  
Re: Cleaning an hp48 keypad
Message #4 Posted by Randy on 24 May 2004, 11:34 p.m.,
in response to message #3 by andy

Any time a key is made electrically, it will not power up correctly. That may explain the behavior you see, I can't say for sure. The just get plain weird when full of stuff as the on resistance of a good key is about 8 to 10k ohms.

Dunk the whole thing so long as the batteries and cards are out of it, no worries about getting things wet, they just take a while to dry out thoroughly.

      
Re: Cleaning an hp48 keypad
Message #5 Posted by David Smith on 25 May 2004, 12:45 p.m.,
in response to message #1 by andy

If you have an ultrasonic cleaner, all the better.

Most people do not realize that most electronics boards go through the equivalent of a big dish washer after they are soldered. Some compenents like dip switches and some piezo beepers are sealed with tape that is removed after the bath.


[ Return to Index | Top of Index ]

Go back to the main exhibit hall