TK-760H won't xmit / briefly xmit

[KC5PGZ]

I have a TK-760H that will key up for approx. 1 second and then no more. It is programmed for ham bands, but appears to do it on all frequencies I program. It actually xmit's for that very brief period. I see it on the wattmeter and with power drawn. Receive is normal.

Finals??? It is prob not worth repairing if so. I do not see anything in the programming software that prevents it. From what I have seen of my other Kenwood radios it is program and go.

Any help is much appreciated

Craig

 

[mmckenna]

What happens when it stops keying up? Does the screen go blank and the radio restart, or is it just not transmitting anymore and switches back to RX mode?

 

[RFI-EMI-GUY]

TX VCO / PLL out of lock?

Any beeps or Boops? was the radio reprogrammed recently? is it in the correct band?

 

[cmdrwill]

Do you have the correct power cable and a properly rated power supply? And did you measure the voltage at the radio?
Troubleshooting 101.

 

[KC5PGZ]

Well, as it turns out, the KISS mentality should be applied. It is repaired... but, I will answer all questions to my question. The radio powers up and receives normally. Radio is programmed for ham frequencies, but I checked it for the actually frequency range it was designed for. Same result.

No beeps or boops, RX is normal and quite sensitive. Voltages and supply are good, I use the same setup for other radios. Radio does not reset or power off.

Radio is on, microphone plugged in. Press mic key. 1 sec xmit. Receive confirmed on handheld radio.
Watt/swr meter deflects and briefly registers output. Let off PTT, wait a few seconds and it will repeat.
Verify programming for any variances (note: I use newer software for other radios, as a result I am not as familiar with the kpg29d version). It appears I had it right.

My curiosity was killing me, so I actually tore radio down and checked a few basic components. And then I tried to most basic simple thing... All of you can slap me. In fact I have already done it!!!

I took the microphone apart. Did you know that the small piece of foam that is glued to the PTT switch can double as a 1 second xmit timer?? Perhaps this is a delayed feature after many years of service!! It worked perfectly, over and over again.

LOL. I recreated it a dozen times before I tore it apart and repaired it. If it hadn't been so perfectly timed, I would have checked the microphone first. In fact, I am guessing the radio was removed from service because of it (not by me)!

To add to this, I didn't have a second compatible mic that was handy to plug in. I always check the microphone with a spare, but this failure was so perfect. Besides, my other Kenwoods use RJ-45 instead of RJ-12 connectors.... excuses - excuses.

Anyway, I detailed my findings for the next fellow that has something similar. This simple problem may apply to many older Kenwood radios with a million miles on them.

Now, I am off to my next project. I am going to convert this radio to be somewhat frequency agile using a DTMF pulse controller for a remote base project. Just need to have the channel up and down capability moved outside the front panel.

Thanks to everyone that responded. All the questions were valid based on what I told you. And now I run away with shame over a stupid microphone!!!!

Enjoy your weekend!

Craig

 

[mmckenna]

Anyway, I detailed my findings for the next fellow that has something similar. This simple problem may apply to many older Kenwood radios with a million miles on them.

Thanks for taking the time to do that. That would have drove me nuts trying to figure that one out.

 

[MTS2000des]

We often get "tunnel vision" as technicians before the basic "is it plugged in?" steps of troubleshooting. I know a guy who tore down an APX6000 to board level thinking it was a top controls flex issue when the culprit was a bad RSM...we've all been there, done that.

 

[WB9YBM]

I have a TK-760H that will key up for approx. 1 second and then no more. It is programmed for ham bands, but appears to do it on all frequencies I program. It actually xmit's for that very brief period. I see it on the wattmeter and with power drawn. Receive is normal.

Finals??? It is prob not worth repairing if so. I do not see anything in the programming software that prevents it. From what I have seen of my other Kenwood radios it is program and go.

Any help is much appreciated

Craig

I'm not familiar with that particular radio but if it's similar to other modern (i.e. post-1970s era) equipment it probably has an SWR sensing circuit that will either cut back xmt power and/or switch back to rcv if the mis-match to the antenna is too great.

 

[DeoVindice]

I had a similar issue with a TK-880 I'd set up with a movable antenna for use in an apartment. If the antenna was too close to the transceiver, RF would get into the unit and shut it off after a moment of transmitting. Problem was fixed by moving the antenna away.