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Kenwood & EF Johnson Forum - For discussion of land mobile radio products manufactured by Kenwood or EF Johnson. For discussion of Kenwood Amateur Radio Equipment, please use the Amateur Radio Equipment forum.

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Old 09-07-2017, 10:06 PM
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Default TK-8180H Faulty Decode

I'm dealing with another school bus radio; it's a Kenwood TK-8180H (not the same one that froze up in my previous post).

It's a spare radio from the shop that I installed in the bus I monitor on each day. I wanted to check it to see how it would work in regular service.

Unfortunately, the frequency our company uses is shared by another user in the vicinity that uses it for data communications, so every few minutes or so, we'll get loud and obnoxious bursts of continuous data through the radios, mainly near the yard.

The company uses a DPL tone, so as long as the microphones are on the clips, the radios keep their squelch closed.

There's definitely something up with this radio. With the microphone firmly grounded in the clip, the squelch on the radio keeps opening and closing. One transmission, the radio quiets the repeater feedback "pop", the next, it comes through loud and clear, followed by a loud stream of data.

I thought it was a loose connection with the microphone, so I swapped it out. The driver and I went out on our afternoon routes today with a different mike. For the first 20 or so minutes, the radio was working as normal, and I thought that the mike replacement did it. Sure enough, after another few minutes, the squelch opened right back up on the radio. The mike had never been touched the whole time.

I plan on replacing the unit tomorrow and bringing it to the mechanic, who will probably say to toss it in the garbage.

Does anyone know what the issue could be? Something loose inside the radio? If I get the radio into my hands, I'd like to fix it.

Off hook decode is an option, but I'd rather not put that on there, if possible.

Thanks in advance!
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Old 09-07-2017, 10:11 PM
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Verify that the clip has a really good ground. I had one act up in a similar manner in one of the apparatus once, turned out that the metal dash structure it was mounted to was only chassis grounded intermittently...and I still don't understand how it could have been that way yet solidly spot welded to the cab structure. A braided strap and a couple of self-tapping screws took care of it.
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Old 09-07-2017, 10:15 PM
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Thanks for the reply!

I'm pretty confident the clip is fine, because there was another radio in the bus before, and that one was working just fine. Same clip, same microphone, different radio, new problem, haha.
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Old 09-07-2017, 11:57 PM
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The radio probably could use an alignment and a squelch setting adjustment
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Old 09-09-2017, 5:03 PM
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DJ11DLN, I guess you must be correct.

I switched the radio with an NX unit yesterday, and I got the same thing. Not as bad, but I'm sure that's just a coincidence. I don't understand it, though, because it was never doing that before, so something must have just happened with the clip.

So here is what I have to work with. Any suggestions?



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Old 09-10-2017, 12:27 AM
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Well, looks like the pictures didn't go through. I don't know; I guess I'll just have to figure it out.
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Old 09-10-2017, 1:24 AM
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It really doesn't matter on a Kenwood if the mic hanger is grounded or not. On the back of the microphone, the microphone housing is connected to ground, while the metal disc on the back of the microphone is held above ground. Look closely, you'll see an insulator between the two pieces that make up the mic disc. As long as the microphone is on the hook, the microphone self grounds through it's internal wiring.

If you're using a magnetic microphone holder ala "Magnetic Mic", the clip ground is essential as you need to disable the internal ground in the microphone.

If you're using a standard mic clip, try bending the metal tab to make better contact with the disc or replace the clip. If the microphone fits loosely in the holder, you'll get strange behavior on any function looking at mic hook status.
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Last edited by KK6ZTE; 09-10-2017 at 1:28 AM..
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Old 09-10-2017, 1:47 AM
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I don't know...anytime there wasn't a good chassis ground to any of the radios I've worked with, there would be a problem. I can't speak to the condition that KK6ZTE describes. I've never known these radios to "self ground" that way. But I admit that my experience is limited...I just know that I've had a situation similar to yours in the past with a bad ground on a mic clip.
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Old 09-10-2017, 2:00 AM
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There is no "condition". There's nothing magical about a ground wire ran to the mic hangar. Take one apart or look at the wiring diagram. Motorola and Icom don't wire their microphones this way, just Kenwood as far as I know.

But I don't know, I just work for a Kenwood dealer
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Old 09-10-2017, 2:05 AM
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And I just deal with these problems as an end user. But that is an "it is what it is" situation.

And neither of us is helping the OP at this point. Hopefully someone who has an angle on this problem will come along and fix that.
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Old 09-10-2017, 11:46 AM
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Well thank you, guys.

The KMC-35 microphone that has been on the bus has a very loose hanger piece on the back of it and the microphone slides around the clip very easily. Either way, I tried a KMC-27 that fit pretty snugly, but that didn't do it, either.

I'll go in there with pliers tomorrow and bend the metal tab on the hanger forward to see if I can get better contact. If I can't, I'll replace the clip. That has to fix it, because there's really nothing else it can be, haha.

By the time I had swapped both the microphone and radio and heard it still making that noise, I was just like, "Well, at least I ruled out 2 out of 3 different problems." Getting a secure ground between the microphone and clip should hopefully do it.
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Old 09-10-2017, 12:50 PM
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Is there any rust or corrosion built up on the mic or the clip?

I've seen more than a few 35 microphones with rust on the rear preventing a good circuit.

Then again, we may have another issue here.

I dealt with a similar issue with a trunked client, but it was interference local to their city. Only bus routes in the city (not the rest of the county) had interference and noise. On of my higher level techs mentioned that some data noise will open PL'ed radios depending on the tone in use.
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Old 09-10-2017, 2:33 PM
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I don't think so. The clip looks clean. The back of the microphone is really scratched up, and there is a lot of brown, but I'm not sure if it is rust or not. Like I said, the back is also really loose, and the microphone spins freely in the clip.

I don't think the second scenario is the case, because the issue is isolated to just this bus, and all the buses are dispatched out of the same yard.

Let's try these pictures again, just for the heck of it.

20170908_170606 by Ryan Kujawski, on Flickr

20170908_170612 by Ryan Kujawski, on Flickr
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Old 09-10-2017, 5:47 PM
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Quote:
Originally Posted by DJ11DLN View Post
Verify that the clip has a really good ground.

The clip does not need to be grounded. The clip it self completes a circuit with in the mic.

If a mic change did not fix the problem, then check out the connector in the control head and make sure the solder on the pins is still good. If that does not solve it, it may need a trip to a service shop.



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Old 09-10-2017, 5:58 PM
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Well like I said, I've gotten this issue on two different radios at this point, an 8180H and an NX-800H, so I'm thinking it has something to do with the clip itself not making good contact with the microphones, not the radios.
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Old 09-10-2017, 7:55 PM
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I had the same thing but different. Fire department that was programmed for off-hook suspends scan. The combination of the mic and clip getting worn/loose/dirty was stopping scan and causing them to miss important traffic. Programming for off-hook scan fixed that.

If you swapped out mics already then a brand new clip is the next easiest experiment.

I have also had problems with (it seems) certain lots of the KMC-35 mic and the RJ-45 connector. Mostly crunchy transmit audio that a good cleaning fails to correct.

If you can set the radio for squelch zero and put it back into non-monitor mode, then you can do the jiggle test to see what causes squelch noise whether it's the clip, the mic connector or whatever.
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Old 09-11-2017, 10:00 PM
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Yeah, I love these Kenwoods, but it seems they can be very problematic.

As of today, I have tried 3 different microphones, but all of them appear to have rust on the back. The third one I tried worked for maybe 20 minutes, but again, the squelch opened right back up.

I made a video while I was doing the jiggle test you were talking about today. Here it is:

https://www.youtube.com/watch?v=llFcibVP03U
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Old 09-11-2017, 10:55 PM
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Yeah, this isn't really much of a problem. Try working on Motorola radios and writing the same code plug for a cdm five times because some radios have a slightly different part number.

Install a new mic and new clip and be done with it. Test swap of junk parts results in frustration. The KMc-35 is less than fifty bucks retail if I remember correctly. It should come with a new clip in the box.

The loose dot on your first mike was definitely why it was so much worse sounding. This isn't anything special, just an electrical circuit. If there is poor contact anywhere in the circuit, you get unpredictable results
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Old 09-11-2017, 11:01 PM
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On a side note, if your bus company is too broke for a new mike, grounding the clip would likely improve the situation, depending on what part of the circuit is iffy. While the ground isn't needed for this application, it may improve your situation.
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Old 09-11-2017, 11:10 PM
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Why not check the 'off hook decode' box and be done with it?


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