The most common failure is the solder joints on the bottom of the boards
under the swithes. That wave soldering process demands that the switches
be held solidly to the board, not floating 1 to 10 thou up it the air.
The solder is many times heavier than the switch so if not solidly held
down while the solder wave goes by, they will float just a hair, leaving
an air gap between the board and the bottom of the switch. This air gap
is closed by the finger pressing the button, which gradually loosens the
grip of the glue holding the copper to the bottom of the board and
eventually cracking the solder joint, leading to a quick double click
effect from the switch closing in response to the finger, then a break
as the crack opens, followed by a second click as the finger lifts again
and the crack closes, then the switch opens again, giving a double click
where the finger made but one push. Those of us that have a hot
soldering iron grafted to a hand can fix that, but we're often
considered rare birds to be avoided by the girls lest the geekiness is
catching. Some of us are even CET's, but that card, laid on the HR desk
has gotten me every job I ever wanted, some quite lucrative.
Cheers, Gene Heskett.
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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http://geneslinuxbox.net:6309/gene>