Good timing. I have just noticed that my 2 button has started acting up. Thanks Paul WB8TSL
On Fri, Mar 9, 2012 at 8:48 PM, <gandal...@aol.com> wrote: > Given the current Loran situation I know this might have come a bit late > but thought it worth sharing in case it's of any benefit to others. If it's > old news then apologies for that but I've not seen it documented > elsewhere. > > Along with other equipment, the 2100 is known to suffer in the long term > from keybounce problems with the front panel tactile switches. > A common "cure" is to increase the keybounce time constant on the 74C923 > keyboard encoders, the 1uF fitted to the 2100 is quite low and I've found > that this can be increased to at least 10uF without adding any additional > problems. > > However, there is likely to come a time when this is no longer an adequate > fix and switches can become severely intermittent or even totally open > circuit. > > Replacements are available from Mouser or Digikey, the current manufacturer > is E-Switch, but with the numbered key caps not being a stock item I > checked my "faulty" switches to see if the caps could be removed and the > original numbered caps transferred to new switches. > > Having found that, with care, the caps can be removed, I also discovered > that these switches are mechanically straightforward and physical failure > is > highly unlikely. > Other than the cap itself, the only moving part in the switch is a metal > "clicker dome" which when depressed shorts across the contacts formed by > the > internal ends of the solder pins used for mounting the switch. > One of these pins is in the centre of the switch, directly below the centre > of the dome, and the other is in one corner with a corner of the dome > plate resting on it. > I'm not sure what the plating is on these pins but, in my switches anyway, > the contact surfaces were heavily tarnished and this was the source of all > the problems. > Prior to cleaning the contact surfaces were dark brown to black and looked > very much like tarnished silver, albeit in this case seemingly > non-conducting. > This tarnishing also seems to have a knock on effect on the gold plating on > the contact surface of the dome so this will need cleaning too. Given that > the dome plate has four distinct corners it's easy enough to ensure that a > fresh corner is used as this contact. > > A small drop of isopropyl alcohol with a folded offcut of cartridge or > printer paper used for burnishing seems to do a good job of removing the > tarnish and polishing the contact areas, I certainly wouldn't recommend > anything > more severe. > After cleaning and reassembly all my switches have a contact resistance of > 0.1 Ohms or less and the unit is fully functional again. I could probably > now reduce the 10uF debounce capacitors but all is working ok so have left > well alone. > > Practical tips.... > > It isn't necessary to remove the switches from the circuit board in order > to remove the caps but it will need a very fine blade or hook to get in > alongside the cap and lever it out. > > What I used has been in my tool kit for years and I'm not even sure what it > is, some kind of sewing implement I think, with a plastic handle and a > bent bent end with the bent section around 3/8 inch long, very hard and > pointed, and not much thicker than a reasonably fine sewing needle. > > The black caps of the flat faced switches used on the numeric keypad and > for the back light switch have a lug approx 1/8" wide protruding downwards > from the centre of each side. These seem to be fairly rugged and careful > leverage alongside the lugs should remove the caps without damage. > > The white caps with a raised tapered section, on the switches along the > bottom of the front panel, have only two lugs, top and bottom, and these > seem > more fragile. > I found it best to lever out the top of the cap first, top being defined as > when viewed in the panel, having broken the end off a bottom lug when > levering one out bottom first, thanks be for superglue:-), but offer no > guarantees that what worked for me will be the best solution for anyone > else. > > Given the cost of replacement switches, plus delivery charges, a few hours > work has saved me over 50GBP, so again I hope this information may be of > benefit to others. > > Unfortunately though, from this point on, you're on your own, you break it, > you fix it:-) > > Regards > > Nigel > GM8PZR > > > > > > > > > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.