HP41 Intermittent Key - Printable Version +- HP Forums (https://archived.hpcalc.org/museumforum) +-- Forum: HP Museum Forums (https://archived.hpcalc.org/museumforum/forum-1.html) +--- Forum: Old HP Forum Archives (https://archived.hpcalc.org/museumforum/forum-2.html) +--- Thread: HP41 Intermittent Key (/thread-9949.html) |
HP41 Intermittent Key - Jim Haselmaier - 07-03-2001 I recently acquired a 41. One key requires 2 presses sometimes before it works. (Its the '2' key, ironically.) Has anyone had this type of problem on this calculator and fixed it? I've found the document in the museum about procedures to fix "Bad Keys". Does anyone know if that procedure is appropriate for the 41? How dangerous is this fix attempt? Thanks.
Jim
Re: HP41 Intermittent Key - David Smith - 07-03-2001 I have repaired NUMEROUS HP41 keys using the wire brush method. Take two or three fine but stiff bristles from a wire brush and chuck them into a pin vise or exakto knife holder. Trim their ends even. Find the offending key on the back of the keyboard. There will be a small hole under it near the center of the key click disk. Place a drop of 91% isopropyl alcohol on the hole, dip the wire brush bristles in alcohol, insert the wire brush bristles and gently "scritch" away at the disk under the hole for a few seconds. Work the bristles all around the hole. Be careful not to break a bristle off in the hole.
This also works quite well on HP25 series machines and possibly others.
Re: HP41 Intermittent Key - Tony Duell - 07-03-2001 That's a neat trick -- I must try it sometime. I think it would work Re: HP41 Intermittent Key - db (martinez, ca.) - 07-03-2001 that wire bristle method sounds like something to try if the dome for that key is flatened and the key dosn't "snap" like the others but if it feels like the others i would first try hosing it down with tv tuner cleaner in case the problem is just dirt. i'll remember that wire trick though.
Re: HP41 Intermittent Key - Jim Haselmaier - 07-03-2001 Thanks a million for the ideas. (This internet thing....even though I've been using it for 12+ years.....continues to astound me.....)
I have a few follow-up questions: Thanks again.
Jim
Re: HP41 Intermittent Key - David Smith - 07-04-2001 All the '41 calcs have four screws, one below each foot. It is quite easy to open and close the '41s. Just be real careful not to overtorque the screws when putting it together again. In particular the upper screw bosses in the case back have a tendency to break because the plastic is quite thin and had become a bit brittle with age (actually HP knew they had a problem here soon after the machines were released). The lower screw posts can also crack off if you get the screws past their limits. Another problem that occurs is the screw posts split vertically. They can be repaired with styrene melting solvent (plastic welder) available at most good hobby shops (Hobbytown carries it). Brush it onto the outside and inside of the cracks, hold the post together for about a minute, then let it set up overnight. The circuit card in the fullnut sits on a conductive elstomer strip (zebra connector) and uses the case tension to hold it in contact with the keyboard.
The half nut designs (rounded LCD display corners) have a single chip surface mounted on the keyboard. They do not have the problems associated with the zebra connector system. Their main problem is the the wires to the piezo beeper disk WILL break off if you even think about opening the case. They are rather thin and the solder connections at either end seems to become brittle with age. Expect that you will have to resolder at least one of them. Feel VERY lucky if you don't.
Re: HP41 Intermittent Key - Tony Duell - 07-04-2001 The first thing to be aware of is that the HP41 is almost entirely MOS circuitry and it _is_ possible to damage it by electrostatic discharge. This damage may not show up at the time, the machine may work when it's put back together and then fail days or months later. |