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Marconi 2022A keyboard bounce, etc.

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Phil_in_CA

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I am new to this forum. I am retired, but worked in the broadcast field in the 70s.

I have a number of pieces of equipment and try to do all of my own repairs, now that I have the time.

My Marconi 2022A has developed the annoying habit of the keyboard either bouncing (lots of digits), unresponsive (the decimal point key!), or just fine.

I have not used it much in the past, but now want to use it more, BUT the keyboard has become a problem, especially the decimal point, which is needed for every instance of frequency inputting and more.

I have succeeded in fixing this kind of keyboard issue in other items in the past, but I had the devil of a time getting it finished and was pulling my hair out by the time it was over... it was very difficult to get everything back together and working.

I am looking for anyone who has had occasion to have repaired their keyboard and has tips about how to do it without the hair pulling or high blood pressure meds! ;)

Thanks in advance!

Phil
 

I get the same problem with remote controls, as well as my Commodore home computers. Each key has a little rubber conductive disk on the underside. When I push a key it touches two copper traces, bridging between them, conducting current.

It misbehaves when tarnish or contaminants get in the way. Many times I've had to fix problems in this way:

1) open the enclosure,
2) further disassemble by unscrewing or unsoldering items,
3) lift the membrane off the board,
4) clean with alcohol or soapy solution,
5) allow parts to dry,
6) remove tarnish on copper surfaces by rubbing with pencil eraser,
8) examine with magnifier, brush away particles,
9) test membrane switches for proper operation,
10) reassemble.
 

I'm not sure what kind of switches that model uses but it sounds like you can fix it by cleaning them anyway.

Dismantle it, if carbon pads are used as Brad comments, clean the carbon pads and silicone rubber cones in cool soapy water then rinse and dry them. For the underlying contact points, if they are metallic , clean them with a solvent. If they are carbon coated (black raised coating) only use soapy water as some solvents will take to coating off.

If they are normal push switches, either replace them or try cleaning them with a 'solvent switch cleaner' but make sure they are dry before refitting.
It is unlikely, but not impossible they are reed switches with magnets under the key caps. They are difficult to repair but a 'dirty trick' that usually works is to leave them for a moment on a degaussing coil or bulk tape eraser. The reeds will rattle at high speed but it seems to clear any contact problems and of course removes any residual magnetism.

Brian.
 

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