davidc@pyr.gatech.EDU (David Carter) (08/08/88)
[Probably more than you ever wanted to know about keyboards. Clip and save; you may have this problem someday] rminnich@metropolis.super.org (Ronald G Minnich) writes: >Well my poor A500 finally got sick. The right side shift key does not work. I have a similar problem; my keypad 0 stopped working. >2) On the bottom of the keyboard are about 10E6 little screws holding >a metal plate. Is this an fcc special or will taking this plate off >allow me to get at what i think may be a cold solderjoint? There are two kinds of Amiga 500 keyboard mechanisms (that I know of). One kind has the metal plate covering most of the bottom, about 30 tiny screws holding the plate, and a small 1" x 6" pc board (containing the 6570 keyboard chip and 3 other small chips). Yours is this kind. The key "switches" are more like what is in calculators: Each keycap pushes down a plastic plunger. At the bottom of the plunger is a rubber, conductive contact. This contact is mashed against two pads on a membrane style pc board, completing the circuit. The membrane lies beneath the entire keyboard, and is connected to the 1x6 pc board. There are no "solder" joints at all on the membrane. In the bad key on my keyboard (and probably yours) the rubber part has stopped being conductive enough. I measured mine with an ohm meter and the value is about 10 times higher than the other keys. Scraping off the top layer of the rubber part made no difference. Incidentally, the rubber piece easily detaches from the plastic shaft (kind of a "insert tab A into slot B" arrangement). Also, the shaft+rubber parts are completely interchangeable. So if you'd rather have your HELP key be the one that doesn't work, you can swap them. The second kind of Amiga keyboard has a single, large pc board which contains the chips mentioned above and individual keyswitches soldered to the board. So if a key went bad on this kind, you could unsolder and replace the offending keyswitch. On an Amiga 500, you need not take apart the machine to see which kind you have. Just look in the expansion RAM port. If you see the metal plate and a small pc board in the upper corner, it's the membrane style. If you see all pc board, it's the other kind. Now for the bad news: After I determined that the only thing wrong with mine was a 5 cent (or less) piece of rubber, I tried my local service center to order a replacement. That part wasn't listed, and the best they could do is offer me a replacement keyboard for $60!! I tried again through Commodore directly. The answer was that they just don't deal with parts that small on the keyboards. However, it had taken so long just to get that answer, that the local Commodore person (thanks Andre!) managed to arrange a keyboard swap, gratis. But I'm still waiting for him to receive the replacement (2+ weeks so far). If you are less fortunate and are forced to buy a replacement, hold on to the old one and sell the parts! I would have paid $5 for a couple of plungers. With 94 keys, you could eventually cover the cost of the replacement keyboard. If only my local service center would have done this... David Carter davidc@pyr.gatech.edu
feb@cbnews.ATT.COM (Franco E. Barber) (08/10/88)
In article <6199@pyr.gatech.EDU> davidc@pyr.gatech.EDU (David Carter) writes: >[Probably more than you ever wanted to know about keyboards. Clip and > save; you may have this problem someday] > >rminnich@metropolis.super.org (Ronald G Minnich) writes: >>Well my poor A500 finally got sick. The right side shift key does not work. > >I have a similar problem; my keypad 0 stopped working. > ... >The key "switches" are more like what is in calculators: Each keycap >pushes down a plastic plunger. At the bottom of the plunger is a rubber, >conductive contact. This contact is mashed against two pads on a membrane >style pc board, completing the circuit. The membrane lies beneath the >entire keyboard, and is connected to the 1x6 pc board. There are no >"solder" joints at all on the membrane. > >In the bad key on my keyboard (and probably yours) the rubber part has >stopped being conductive enough. I measured mine with an ohm meter >and the value is about 10 times higher than the other keys. Scraping >off the top layer of the rubber part made no difference. Incidentally, >the rubber piece easily detaches from the plastic shaft (kind of a >"insert tab A into slot B" arrangement). Also, the shaft+rubber parts >are completely interchangeable. So if you'd rather have your HELP key >be the one that doesn't work, you can swap them. > ... >David Carter davidc@pyr.gatech.edu Well, this idea might help somebody with a bad keyboard. I have several remote controls for TV, stereo, VCR, etc. The volume-down button on one of them stopeed working one day. I took the remote apart and found the same rubber plunger pushing against membranes on a pc board construction that is described above. The rubber plunger had too high a resistance. I was able to revitalize the contact by covering the face of the rubber contact with some conductive paint I bought at a local electronics parts store. The name of the product I found is "Nickel Print". It is distributed by GC Electronics, Rockford Illinois, 61101. Catalog No. 22-207. This products seems to be designed for making repairs to PC boards. I had a little trouble making the paint stick to the slippery rubber plunger. I had to scratch the face of the rubber plunger to give the paint a good surface to grip onto. Franco