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hp25 on/off switch - Printable Version

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hp25 on/off switch - thaddeus boruta - 04-17-2004

My hp 25 on/off switch has given up the ghost.(It used to repond after 1 or 2 on-off cycles, eventually it took many off-on cycles, now it does not respond.)
I had taken the circuit board out, and found the switch location, but it looks like i would have to cut through the welded plastic attachment buttons to get at the switch. I fear that that would create a bigger problem than my off-on switch. Does anyone have any suggestions? Thank You, Thad

Re: hp25 on/off switch - David Smith - 04-18-2004

If your keyboard version is the type with the holes under each key you may be able to clean the switch contacts using a small wire brush made up of three bristles twisted together, inserted into a pin vise, and trimmed flush. Place a drop of 91% isopropyl alcohol onto the hole under the switch contact, dip the brush into more alcohol, and gently "scritch" around in the switch hole. Some HP25 keybaords have a hole near each end of the switch contacts. If so, do both holes. This technique is not nearly as effective on HP25 power switches as it is on the key contacts...

Re: hp25 on/off switch - Jon - 04-18-2004

I have repaired that problem removing the full keyboard. You have to eliminate the less possible plastic. If you do it properly you will have material enough to fix the keyboard again using a hot tool.

Re: hp25 on/off switch - thaddeus boruta - 04-19-2004

Thank you; I will try it.

Re: hp25 on/off switch - thaddeus boruta - 04-19-2004

Thank You for the help. Are there many loose pieces that fall out when you take the back of the circuit board off?

Re: hp25 on/off switch - Vieira, Luiz C. (Brazil) - 04-19-2004

Hi, Thadeus;

I was about to post something too, but David and Jon already managed to help you. (this site rules...)

About loose parts: all keys become loose, so don't turn the upper case "up" again unless you plan to hold the keys; also, four others: the two black, plastic sliding switches themselves ([ON OFF] and [PRGM RUN]) and the metal contacts underneath them.

The "function" keys may sometimes be held in place by a sheet of flexible plastic that is found in most Woodstocks (2X series), so you may also keep them in place easier. If you decide to remove the keyboard PCB in order to clean the upper case, beware of two important facts: if using water and some sort of neutral detergent, some inks used in some models may smear and fade; avoid this procedure if you don't need to clean the upper case. When placing the keys back, make sure to check their positions before "gluing" the keyboard back in place; sometimes it happens that some keys are placed in wrong position, and returning them back to their original place after fixing the keyboard means removing the keyboard PCB again... So, double and triple checking means no headache.

The metal contacts in both [ON OFF] and [PGM RUN] keys are sometimes grasped to the keyboard by the "grease" used to reduce the friction between the metal contacts and the printing board.

Hope this helps a bit.

Edited: 19 Apr 2004, 2:15 p.m.

Re: hp25 on/off switch - thaddeus boruta - 04-19-2004

Dear Mr. Luiz,
Thanks for the tips. I will try the "no cutting" method first. . . . . this calculator has been so much a part of me, that I will have to "get my courage up" before i can start "operating." Thanks again, Thad

Re: hp25 on/off switch - David Smith - 04-20-2004

I have never seen a disassembled keyboard that went back togther again quite the same. One thing that is worth a try may be to give the keyboard a bath in an ultrasonic cleaner. I use three baths of fresh distilled water between each cycle. Shake as much water out of the keyboard after each bath. Dry the keyboard in an oven on low (like 140 F) overnight.

Re: hp25 on/off switch - bill platt - 04-20-2004

And remember---TAKE THE BATTERIES out first! :-)

Re: hp25 on/off switch - Tony Duell - 04-20-2004

I'd love to see anyone dismantle a Woodstock-series calculator without taking the battery pack out :-)

Re: hp25 on/off switch - bill platt - 04-20-2004

Hi Tony,

I interpreted the ultrasonic technique as applying to the entire calculator--I was thinking of the Pioneer cleaning regimen!



Re: hp25 on/off switch - Jon - 04-21-2004

Hi David:

I have disassembled several woodstock keyboards and the result when reasembling was perfect. The same for HP-41 calculators. If you take care and remove the minimum plastic (resulting a plastic cilinder) you can use a hot tool later and the result is just perfect.

Sorry for my english. If somebody needs more detailed information I can try it.


Re: hp25 on/off switch - David Smith - 04-21-2004

If you can get the machine apart you only need to clean what needs to be cleaned. Pioneers don't come apart gracefully so they get dunked whole.

Re: hp25 on/off switch - Tony Duell - 04-22-2004

Pioneers come apart very easily. It's putting them back together that's the hard part ;-)

Re: hp25 on/off switch - David Smith - 04-22-2004

Been there, done that... or at least tried. My $1 HP42 is still a bit lumpy.