[time-nuts] Austron 2100 switch repair
paulswedb at gmail.com
Sat Mar 10 05:31:45 UTC 2012
I have just noticed that my 2 button has started acting up.
On Fri, Mar 9, 2012 at 8:48 PM, <GandalfG8 at 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
> 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
> 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
> 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
> 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
> 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
> 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
> 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
> 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
> 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:-)
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