Kenwood: TM-281 xmit problems

[sloop]

My TM-281 will not transmit installed in my 2017 Nissan truck. The unit turns off and then resets whenever I try to transmit (high or low power), Kenwood says its a power supply problem.
1. Unit transmits when connected to AC supply
2. DC (truck) pos. supply connected directly to battery, gnd. to ground bar near battery
3. Battery is less than a year old
4. SWR is 1.2 to 1
5. Receive works fine
Anyone with any ideas, I'm at my wits end because electronically it should work.

 

[bharvey2]

I've run across that problem in the past. Not with a TM-281 but with other radios. Kenwood is giving you good information. You likely have a bad connection somewhere. On receive, the current draw of your radio isn't very high so it works properly. When you transmit, the current draw is much higher and the bad connection causes a voltage drop which in turn, causes the radio to reboot. Given the symptoms you describe, I'd clean and reestablish every connection point between the radio and the battery. That would also include everything between the battery and vehicle ground. Also, make sure your power conductors are properly sized; 12ga minimum, larger if they are of any appreciable length.

 

[mmckenna]

I agree. Go through and check all the connections.
The fuse holders can likely be a cause, depending on the type. I would use a separate fuse block and not the ones that come built in on the factory power cables.

Recrimp all your connectors with a good set of crimpers.

Really does sound like what bharvey2 says above.

 

[KevinC]

My TM-281 will not transmit installed in my 2017 Nissan truck. The unit turns off and then resets whenever I try to transmit (high or low power), Kenwood says its a power supply problem.
1. Unit transmits when connected to AC supply
2. DC (truck) pos. supply connected directly to battery, gnd. to ground bar near battery
3. Battery is less than a year old
4. SWR is 1.2 to 1
5. Receive works fine
Anyone with any ideas, I'm at my wits end because electronically it should work.

Couple of things…

What’s the voltage drop at the radio when you key up?

How close is the antenna to the radio? Sometimes high RF can get into radios and do weird things.

 

[sloop]

I have not measured the voltage drop....did not even consider that. If there is a voltage drop what would cause that? I have checked the connections and they are good. The voltage line is the one that came with the radio. The antenna is approx. 4 feet away in the bed. I did have it mounted on the fender abt. 2 ft. away and the radio behaved the same.

 

[bharvey2]

Resistance to current flow causes the voltage drop. Poor connections are likely sources of resistance. As the current flow increases, the voltage drop across the resistive connection becomes more prominent. (Do a Google search of Ohm's Law if you are unfamiliar with the concept. )

You mentioned in your original post that when you power the radio with an AC supply that your radio doesn't reboot. Are there any other changes? Is the radio still mounted in the truck? Are you using the same power cable with the AC supply as you are using with the battery? Even if the mating connections at the end of you power cable is good, you might still have a bad connection between the battery and the vehicle ground. It isn't uncommon for those connections to go bad as a car ages.

 

[sloop]

Checked and no voltage drop between receive and transmit. Only difference between AC and DC is the length of the cable (truck vs. house). I will go back and check all connections and fuse holders (spade type). As difficult as this has been to find it must be something simple! Thank all of you for your insight, it has been helpful.

 

[sloop]

When all else fails I will replace the electrical wiring to the radio with a new line.

 

[bharvey2]

Checked and no voltage drop between receive and transmit. Only difference between AC and DC is the length of the cable (truck vs. house). I will go back and check all connections and fuse holders (spade type). As difficult as this has been to find it must be something simple! Thank all of you for your insight, it has been helpful.

Where are you measuring for the voltage drop? The best place do do it would be as close to the radio as possible. You may be able to reach into the back of the connector closest to the radio with either your meter probes or with something like paper clips and measure there. Bear in mind those that with some meters, their reaction may be too slow to be noticeable as the radio reacts and reboots. Believe it or not, this might be one case where an analog volt meter has an advantage.

You mentioned that the only difference is the cable length (truck vs. house) This suggests lot of variables. Can you keep your radio mounted in your truck and bring your AC power supply out to the truck?

 

[sloop]

I measured the voltage drop with an analog meter (that's all I use) at the connector nearest the radio (about 4 in. from the radio).
It will take some time, but I will try the AC power at the truck as soon as I have time. Good thought to do that...this way all things are equal but voltage source.

 

[WA0CBW]

What was the drop?
BB

 

[bharvey2]

What was the drop?
BB

In a few posts above, he states that he didn't note a voltage drop. Too short of a duration to read? Perhaps.

 

[sloop]

ok, update on radio, I've found the problem.....ITS GREMLINS !!! Not having ventured under the hood yet, I decided to check the antenna one more time. I hooked a dummy load to the radio and the radio xmit worked. Reconnected the antenna and.....the radio still worked. So it must be Gremlins. I'm going to go ahead and switch out antenna and move the mount to where it use to be and eventually replace the electrical wire from the battery. So this is my last reply...thank you for all of the good in site, it has been really helpful to someone that had thought of every avenue to check. 73's

 

[sloop]

PROBLEM FOUND!!!!! Although I suspected Gremlins by accident I found the real problem. After having changed antennas, mounts, cables, and power connections, I was re-installing the radio and testing it. At first it worked then I moved the mike cable and it stopped working. I found that if I 'wiggled' the mike connector it would cause the radio to work or not to work. So the problem is in the connector (mike side or radio, I don't know which). I knew that there was a reason I disliked the modular plug for mikes. I am convinced that the only reason they are used is that they are cheap. I hope that this helps anyone with similar problems with their radios not just Kenwoods.

 

[mmckenna]

RJ type connectors are not bad, a lot of commercial radios use them.

The important part is to utilize some sort of strain relief. In our patrol cars, we use a small cable clamp to hold the mic cord to one of the face plate mounting screws. I make sure to leave a good loop of cable going to the radio. That puts all the strain on the cable clamp.

The Motorola radios that use RJ type connector often have a metal hook near the plug end of the mic cord. Those were designed for attaching the mic cord to the mounting bracket.

I've never had an issue when the mic cord is installed like that. I have had failures where that was not done.

 

[sloop]

Thanks mmckenna, excellent advice. I will take care of that as soon as I determine which connector I need to replace if any.

 

[chief21]

I found that if I 'wiggled' the mike connector it would cause the radio to work or not to work. So the problem is in the connector (mike side or radio, I don't know which).

Suggest you check the RJ connector (on the radio side). Sometimes the tiny copper wipers inside the RJ connector can get bent or crossed and two or more of the wipers will short out. Get a good light and visualize the inside of the connector to verify that all of the wipers are straight and not bent.

 

[sloop]

chief21...thanks, that is a good place to start