Kenwood TK790 does not transmit

[K0ERZ]

Hi Guys,

I looked around and saw the most Kenwood knowledgeable people here so I was hoping you could help me.

I recently got a TK-790 from a surplus store. I also bought a programming cable and have been able to program the radio with the KPG-44D software so I assume I have the stock version.

The radio works well and responds to button presses. I do not have an external speaker at the moment so I don't know if I have audio. I have been able to tighten the squelch via the software and now it seems that the busy light does not show with the squelch above 8 so I hope I fixed that for the moment.

My problem is that is does not transmit at all. I have a 9-pin Kenwood mic and the contact tests fine. However no matter what I try I can't seem to get the unit to transmit. Poking around inside it seems fine. Nothing is burnt or weird looking.

In short I am stuck. I hope some of you know this radio better and can help me.

Thanks!
Erez
K0ERZ

 

[discombobulated]

So when you press the PTT on the mic no red light indication on the head? Do you see any current draw? What are you transmitting into? If I remember correctly there is a PTT relay that from time to time would go out.

Sent from my SAMSUNG-SGH-I337 using Tapatalk 2

 

[K0ERZ]

No red light, no current draw on the PS meter.
I'm connected to a 1/4 wave whip via a 17 ft rg-58.

Do you know where this relay is?

 

[MTS2000des]

Dumb basic question but is your transmit not disabled in KPG? And is a straight up 790 or 790H, what kind of power supply (current wise) are you supplying?

The 790 mid power requires a 10-12 amp supply, the H version 20 amps minimum.

If voltage/current is too low the radio will not transmit.

 

[K0ERZ]

I'm not sure. I looked in KPG and did not see any settings to disable Tx. Tough program to understand.

I'm using a 12v 7A PS. I'll try it with a battery to see if I get anything different... Report back soon!

 

[com501]

Remote head, or local. If it is local, you need to put the jumper on the correct pins on the rear of the transceiver for audio at the head.

What type of head? Does it have ALL buttons, or is there a speaker in it?

The next answer from you will determine where I tell you to install a +12v lead to enable ignition sense PTT inhibit. But we need to know WHAT kind of head, HOW it is installed, and whether it is the 100 watt H version of the 50 watt medium power version.

 

[K0ERZ]

Remote head, or local. If it is local, you need to put the jumper on the correct pins on the rear of the transceiver for audio at the head.

What type of head? Does it have ALL buttons, or is there a speaker in it?

The next answer from you will determine where I tell you to install a +12v lead to enable ignition sense PTT inhibit. But we need to know WHAT kind of head, HOW it is installed, and whether it is the 100 watt H version of the 50 watt medium power version.

It's the 50w version. Local head. All the buttons (no speaker)

 

[wwhitby]

I'm not sure. I looked in KPG and did not see any settings to disable Tx. Tough program to understand.

For the channel that you are trying to transmit on, make sure you have a frequency programmed in the RX and the TX column. If you don't have one on the TX column, it becomes receive only.

 

[K0ERZ]

For the channel that you are trying to transmit on, make sure you have a frequency programmed in the RX and the TX column. If you don't have one on the TX column, it becomes receive only.

Ah, OK. Yes, I do have both freq's programmed.

 

[K0ERZ]

Quick side question.... Can I completely disable the ignition sense (so I don't need the extra wire)?

 

[K0ERZ]

Here are some images, maybe you guys can decode what it is better

 

[com501]

The programming software on the 790 has nothing to do with ignition sense. There are surface mount zero ohm resistors in the power section that control that. This radio may very well be set up that way.

You need to have the manual to compare what is installed in the radio to the manual. You definitely need to install a speaker, your radio may be out of lock, and the only indication of that, short of test equipment or a volt meter hooked to the VCO is a speaker complaining when you key the mike.

 

[AA4TX]

I'm not sure. I looked in KPG and did not see any settings to disable Tx. Tough program to understand.

I'm using a 12v 7A PS. I'll try it with a battery to see if I get anything different... Report back soon!

A 7 amp supply might be your issue. This is not sufficient for this radio. I would expect similar behavior due to overloading of the power supply. A battery test with a sufficient battery would give you a clue.

John
AA4TX

 

[K0ERZ]

Nope, hooked it up to a car battery and still nothing. I would get having the TX switch off or do a short transmit and stop but it isn't doing ANYTHING. No click, no light, no current draw.

Other than that it works well. I moved R504 to R506 and R742 to R743 so now it doesn't need the ignition wire but I'm stumped with this Tx thing.

 

[AA4TX]

I would try one more thing. Use a dummy load to ensure that you do not have some sort of RF entering where it is causing a problem. If that fails, you should look to see if you get a spike of excessive current on TX. An analog amp meter would be in order here.

John
AA4TX

 

[K0ERZ]

OK, I solved it!!!

Absolutely annoying and stupid!

I got fed up and started poking around with a multimeter. I tested the mic and it worked fine. Everything with the radio checked out. What the heck is the problem then?

I took the head off and tested the leads coming off the mic. No response from the PTT. Aha! problem here. So I checked the mic again and it was fine .
Looking into it I can now see that the connector is twisted ~15 degrees. What!?!??! How did that happen? Took it off and "persuaded" it to come around. Plugged back in and voila! The darned thing transmits!

Now I just have to wait for the external speaker and hope that works....


Thanks for the help guys!!!!

 

[com501]

I haste those stupid round connectors on the 90 series. They come apart very easily too, or you get the ones in where the operator screwed the thread on so tight that they sheared it off. New control head front time.

 

[MTS2000des]

I haste those stupid round connectors on the 90 series. They come apart very easily too, or you get the ones in where the operator screwed the thread on so tight that they sheared it off. New control head front time.

yeah, and what FUN it isn't removing two dozen screws having to replace an entire control head front because some moron used a Rototorque or air wrench to tighten that thumbscrew!

 

[K0ERZ]

How do I take the connector apart?
I just twisted it but I want to see if I can make the fix better.

 

[com501]

The inner guts just 'snap in' to the outer frame of the connector. Don't be surprised if you bust a wire getting it apart. The good news, is the mike cable is a modular replacement and unplugs from the base of the microphone.