Kenwood: Kenwood TMV71A MC 59 issue

[kt8r]

Looking for help on the following issue: MC59 Mic does not key or light up when plugged in the rig. I tried the mic in an old TM261A and it worked and lit up. I tried the mic from the TM261 in the TMV71 and it keyed the rig, but the buttons and encoder were not functional.
Before I open the rig up, is there a problem with this that Kenwood has not let be known?
Yes, it worked just fine the last time I used it. One person did make mention of a pecking noise the last time I used the rig, which would be a key decoding issue I believe.

Thanks

 

[cmdrwill]

A known problem, both the ''pecking noise" and the non functioning buttons.

First clean the 8 pin mic plug with contact cleaner. Some mics have a jack in the mic and a plug on both ends of the mic cord, clean those too. Clean the pins in the mic jack on the radio.

Some times I have to replace the cord due to poor crimping of the 8 pin connectors,

 

[kt8r]

Most likely this is internal. The mic is fully functional on another rig as I stated.

 

[MTS2000des]

This sounds a lot like your problem.
Apparently a small pico fuse exists on the main PCB that blows. An easy fix, but a PITA to get at.

 

[kt8r]

I have transmit, I have audio, but for whatever reason, this rig does not like the stock mic anymore. I can key it with another mic, I can key it with a Heil PTT, while using the Heil PR77, the stock mic works on another rig. So, maybe a sledgehammer is in order? Hi Hi.
Only thing I can surmise is the rig has something that is consistent with a cold joint. It worked the day before it quit. Also, does the mic require voltage to work? It had voltage on the other radio and lit up. I am thinking this might be the issue.

 

[cmdrwill]

Kenwood mic:

Needs 8 volts from the radio via the mic jack for the electret element.
Has two different grounds, one for the mic audio. Another for PTT switch.
Buttons and illumination use the second ground.

Heil mic does not use the 8 volts and is wired different as to the grounds.

Have seen and repaired lots of V71/ D710 radios that had burned up traces on the circuit board to mic jack. As noted, it is a ***** to get at.

 

[kt8r]

This sounds a lot like your problem.
Apparently a small pico fuse exists on the main PCB that blows. An easy fix, but a PITA to get at.

Briefly, where is this fuse located before I tear this thing down? I would appreciate it.

 

[cmdrwill]

Briefly, where is this fuse located before I tear this thing down? I would appreciate it.

Step 1: Get the Service manual.
Step 2: It IS a ***** to get to, have to disassemble the radio.

 

[kt8r]

Step 1: Get the Service manual.
Step 2: It IS a ***** to get to, have to disassemble the radio.

Already have it downloaded. I noticed a fuse that goes to ground off the mic connector inside the rig. Is this the one?

 

[cmdrwill]

Already have it downloaded. I noticed a fuse that goes to ground off the mic connector inside the rig. Is this the one?

One of the problems, page 84, check the 0 resistors R960 R962 also, check the solder on all the jack to PC board connections, they are known to break loose from the circuit board.

You can check the two, ground and ME, pins with an ohm meter. Just remember Kenwood numbers the mic jack pins backwards from the RJ45 standard.

 

[kt8r]

This sounds a lot like your problem.
Apparently a small pico fuse exists on the main PCB that blows. An easy fix, but a PITA to get at.

Yep, after all this time, I decided to investigate the issue. It was that damn little fuse. I replaced it with a small old style glass fuse holder. Works like new now. Just have to disassemble the whole rig to get at it.

 

[MTS2000des]

Yep, after all this time, I decided to investigate the issue. It was that damn little fuse. I replaced it with a small old style glass fuse holder. Works like new now. Just have to disassemble the whole rig to get at it.

Dear Kenwood,

If you're going to put a fuse or picofuse in a circuit, please make it easier to get at than burying it as deep inside a radio as possible.

Thank you,

Radio technicians everywhere