NOTE: Crossposted to rec.radio.amateur.equipment and rec...homebrew.

For some years, I've had a Kenwood TM-251A 2-meter xcvr (with 440 rcv)
hanging from the ceiling of my pickup truck, and recently the TouchTone
pad (in the microphone) quit working and, while PTT causes plenty of RF
output, there's no AUDIO output.

I'm pretty sure the problem is in the microphone electronics OR its
8-wire cord. I've "beeped" the cord from the telephone/data-like (RJ-45?)
connector to solder joints on the mike PC board (it's quite a full little
board!) and don't find anything wrong (but it's hard to hold a probe on
each end and wiggle everything in the middle!). I'd replace the cord in
a flash except I can't handle that %$#@! RJ connector.

The only microphone detail in the xcvr Service Manual other than the
connector pinout:
UP
+8 volts (I measued +7.25)
GROUND
PTT
ME (Mike Earth?)
MIKE
RD (Read Detect? An output, perhaps for use with a TNC?)
DOWN
is the fact that PTT, UP, DOWN, CALL, VFO, MR, and PF are connected to
three analog-inputs (and ground), thus "using up" four of the seven
input wires and leaving just two wires (MIKE and ME) to handle the
remaining 16 TouchTone keys AND audio!

PTT, UP, DOWN, CALL, VFO, MR, and PF do work as they are supposed to.

With "Remote Control Mode" ON, letter "A" on the TT pad is supposed
to start frequency input from the keypad, but it does NOT. With an
oscilloscope probe on the MIKE and ME wires, pushing "A" gives no
visible change in the trace, but my jury-rig setup would probably miss
a single tone-burst, so that is probably an inconclusive test other
than the xcvr CPU didn't respond, either.

Any suggestions?

--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448
NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol)

wrote:
each end and wiggle everything in the middle!). I'd replace the cord in
a flash except I can't handle that %$#@! RJ connector.

Look for a Cat5 computer LAN patch cable; cut off one end. It won't be
coiled but it will be flexible & the plug will already be there for you.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

wrote:

NOTE: Crossposted to rec.radio.amateur.equipment and rec...homebrew.

For some years, I've had a Kenwood TM-251A 2-meter xcvr (with 440 rcv)
hanging from the ceiling of my pickup truck, and recently the TouchTone
pad (in the microphone) quit working and, while PTT causes plenty of RF
output, there's no AUDIO output.

I'm pretty sure the problem is in the microphone electronics OR its
8-wire cord. I've "beeped" the cord from the telephone/data-like (RJ-45?)
connector to solder joints on the mike PC board (it's quite a full little
board!) and don't find anything wrong (but it's hard to hold a probe on
each end and wiggle everything in the middle!). I'd replace the cord in
a flash except I can't handle that %$#@! RJ connector.

The only microphone detail in the xcvr Service Manual other than the
connector pinout:
UP
+8 volts (I measued +7.25)
GROUND
PTT
ME (Mike Earth?)
MIKE
RD (Read Detect? An output, perhaps for use with a TNC?)
DOWN
is the fact that PTT, UP, DOWN, CALL, VFO, MR, and PF are connected to
three analog-inputs (and ground), thus "using up" four of the seven
input wires and leaving just two wires (MIKE and ME) to handle the
remaining 16 TouchTone keys AND audio!

PTT, UP, DOWN, CALL, VFO, MR, and PF do work as they are supposed to.

With "Remote Control Mode" ON, letter "A" on the TT pad is supposed
to start frequency input from the keypad, but it does NOT. With an
oscilloscope probe on the MIKE and ME wires, pushing "A" gives no
visible change in the trace, but my jury-rig setup would probably miss
a single tone-burst, so that is probably an inconclusive test other
than the xcvr CPU didn't respond, either.

Any suggestions?


Have you checked at the rig end? I've had broken or intermittent
connections to the mic socket - the socket pins have poor soldered joints.

Bob

--
Everything gets easier with practice, except getting up in the morning!

wrote in message ...
NOTE: Crossposted to rec.radio.amateur.equipment and rec...homebrew.

For some years, I've had a Kenwood TM-251A 2-meter xcvr (with 440 rcv)
hanging from the ceiling of my pickup truck, and recently the TouchTone
pad (in the microphone) quit working and, while PTT causes plenty of RF
output, there's no AUDIO output.

I'm pretty sure the problem is in the microphone electronics OR its
8-wire cord. I've "beeped" the cord from the telephone/data-like (RJ-45?)
connector to solder joints on the mike PC board (it's quite a full little
board!) and don't find anything wrong (but it's hard to hold a probe on
each end and wiggle everything in the middle!). I'd replace the cord in
a flash except I can't handle that %$#@! RJ connector.

The only microphone detail in the xcvr Service Manual other than the
connector pinout:
UP
+8 volts (I measued +7.25)
GROUND
PTT
ME (Mike Earth?)
MIKE
RD (Read Detect? An output, perhaps for use with a TNC?)
DOWN
is the fact that PTT, UP, DOWN, CALL, VFO, MR, and PF are connected to
three analog-inputs (and ground), thus "using up" four of the seven
input wires and leaving just two wires (MIKE and ME) to handle the
remaining 16 TouchTone keys AND audio!

PTT, UP, DOWN, CALL, VFO, MR, and PF do work as they are supposed to.

With "Remote Control Mode" ON, letter "A" on the TT pad is supposed
to start frequency input from the keypad, but it does NOT. With an
oscilloscope probe on the MIKE and ME wires, pushing "A" gives no
visible change in the trace, but my jury-rig setup would probably miss
a single tone-burst, so that is probably an inconclusive test other
than the xcvr CPU didn't respond, either.

Any suggestions?

Our local university club had one of these that was flakey as well, it had
been hit by lightning and both receivers worked, but from the testing I did
on it, the ptt no longer worked as ptt, one of the freq change buttons now
worked as ptt, but locked on when pressed once, then turned off when pressed
again. The other buttons on the mic were similarly mangled up. No one wanted
to spend money to actually fix the piece of junk, so it just got shoved in a
box and stored away. Good luck on getting yours running, I was not impressed
by the recieve audio, and with the transmit problems with the one we had I
never did listen to its transmit audio.
thanks, John.
KC5DWD