Erratic HP 9100B

[Cosmo]

Dear All, I got an old 9100B that works erratically. To be precise it lights up but the CRT disappears after keying some specific keys, mostly advanced scientific functions such as the trig, log, exp. The remaining basic functions (add, multiply, square root and so on) work well including storage in the various registers. Opening the calculator I saw that the gummy wheel was entirely disintegrated and the gum fell on the mainboard (gummy spots). What would be the best way to remove those gummy spots (which chemical are safe) ? Thanks in advance for your kind help regarding such a wonderful machine.

[TASP]

I was in sparky school around 1982, if I recall correctly (LOL), in that era we were using an aerosol degreaser/cleaner to clean the circuit boards we made and worked on. I know it cleaned up rosin core solder residue really well.

I can't remember the exact hydrocarbon/fluorocarbon that was in the spray, I am sure it causes cancer, was radioactive, destroyed the ozone, was derived from asbestos and killed puppies and kittens. Might want to wait for a way better answer than I'm putting here.

Your device, IIRC, is older still, so I don't know if stuff from the 80s would be safe on stuff from the 60s. Same for whatever they use today; would it be safe for something that old made of materials they don't make anymore??

I think you are on to something with the rubber crud needing cleaned up. Hopefully it is just conductive enough to mess up the 9100 logic. If it is corrosive too, you might have a far more serious problem.

[Cosmo]

(04-30-2015 04:59 PM)TASP Wrote:  I was in sparky school around 1982, if I recall correctly (LOL), in that era we were using an aerosol degreaser/cleaner to clean the circuit boards we made and worked on. I know it cleaned up rosin core solder residue really well.

I can't remember the exact hydrocarbon/fluorocarbon that was in the spray, I am sure it causes cancer, was radioactive, destroyed the ozone, was derived from asbestos and killed puppies and kittens. Might want to wait for a way better answer than I'm putting here.

Your device, IIRC, is older still, so I don't know if stuff from the 80s would be safe on stuff from the 60s. Same for whatever they use today; would it be safe for something that old made of materials they don't make anymore??

I think you are on to something with the rubber crud needing cleaned up. Hopefully it is just conductive enough to mess up the 9100 logic. If it is corrosive too, you might have a far more serious problem.

Thanks very much indeed for the advice. I would be fine for me to know, since errors (display vanishes and I am obliged to switch off the calculator) are related to the use of advanced math functions, if a specific board might be involved in this problem. I guess some HP 9100A/B users experienced similar problem in the past ? Thanks for your help.