[Kenwood] TM-261A Trasmit Problem

[Dr. Gerald N. Johnson, electrical engineer]

The more common problem with the TM-261A microphone is failing to
operate PTT. The PTT switch is different than all the rest. Its operated
from the side button through (originally) a foam button that is too weak
to reliably push the snap switch that mounts at right angles to the PC
board. Its generally cured by adding super glue to the foam to stiffen
it or by replacing the foam with a 4-40x1/4 screw. If the screw is set
too long, it could eventually damage the switch and that seems likely in
your case. It could be that the cable has not been anchored well at
either end (more likely the plug end) and has shorted some wires. That's
been happening to microphones in mobile service for the last 75 years,
no reason it can't happen now.

There are other possibilities involving the use of varying resistances
to ground to cause different operations and the drifting of resistors
and controller thresholds. Possibly an audio (tone or voice) coupling
capacitor to the same wire has gotten leaky and is holding the PTT just
far enough to keep it from releasing. Probably an electrolytic.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.