[R-390] R-390 Power-on micro switch

[Bill Smith]

Interesting venture tonight.  Attempted to use the R-390 to tune into Amos
'N Andy (7415) tonight at 9:00pm PDT, but the receiver wouldn't turn on.
Ha, the notorious micro switch had failed.  It had been difficult to turn
off the receiver in the recent past, but this was the first time I couldn't
get it to turn on.

Leaped over to the SX-62, then embarked on the project to remove the R-390
front panel.  That done, and the switch unsoldered and in my hand, a cover
was removed by the careful application of a pick to press out two
friction-fit pins.

Once inside, overheating was evident.  The plastic cover was melted to the
extent it interfered with the operation of the micro switch contact
assembly.  But the switch contact, though intact and toggling correctly,
wouldn't pass a continuity check with an ohm meter.

A file evened out the melted plastic, but in spite of burnishing the
contacts, there was still resistance between switch points.

Careful measurement yielded the culprit.  The (silver?) contact button on
the business end of the middle leaf was swaged into the leaf, but was not
making electrical contact.  Apparently this small spot was generating the
resistance that had generated enough heat to melt the plastic.  The apparent
solution was to apply a spot of solder between the of the wafer and the
button.  'Twasn't easy, the metal had to be filed a little before it would
adsorb solder.

Another ohm check with the Simpson 270 verified "0" ohms resistance when the
switch is operated.  The micro switch was reassembled and the receiver put
back together.  We'll see how long it works, but I wonder if a new switch is
available?

Hopefully the R-390 will run with the repaired switch for a while.

73 de Bill, AB6MT
billsmith@ispwest.com