KMC-35 Microphone Not Working on TK-8150

[kenwoodgeek]

Just a quick question.

We got a bunch of brand new school buses in at my company. We installed TK-8150s in these buses. We ran out of radios (new ones arriving on Monday), so we had to install an 8150 from an older bus.

This particular 8150 seems to ONLY accept KMC-27 microphones. We have brand new, in the bag KMC-35s that we want in these buses, but they won't work. I plug them in, but when I hit the PTT, the radio does not key. Tried two different 35s and two different 27s. 27s work, but 35s don't.

Most of the few 8150s in our buses are using KMC-35s and work flawlessly. Never seen this issue before. Is there a way to correct this? Maybe a firmware update on the radio?

 

[mmckenna]

The microphones use the same pinout, but the circuitry is a bit different on the PTT side.
Check to see if the mic settings or the external mic port on the DB-25 match the other radios.

 

[kenwoodgeek]

Like I said, on all the rest of our radios, the mikes are interchangeable. Most of our 8150s are running KMC-35s perfectly. And a couple of our NX-800s and TK-8180s are running KMC-27s. I borrowed a KMC-35 from a different bus with an 8150. Tested it and worked fine. Then moved it to this 8150, and nothing. Moved it back and worked fine again. I would think there has to be something more to this.

 

[kenwoodgeek]

Sorry, just saw the edit you made to the reply. Will check that out!

 

[n0fwg]

My guess based on similar problems in a NX-820 radio
One of the ground traces in the radio is open, either burned open or liquid got in. The KMC-27 uses a direct path for the PTT switch where as a KMC-35 uses a transistor switch for the PTT>

 

[kenwoodgeek]

That is helpful information; thank you very much. I have a good-working TK-8150, at this point, that I am going to swap into the bus. The radio in question will come home with me so I can take a look at it. I will inspect it and report back.

 

[n0fwg]

I repaired another NX-820 with the same problem. This one had slight liquid damage under the mic jack where the B+ line had some corrosion on a feed through.

 

[kenwoodgeek]

Hmm, interesting. So I guess that does happen periodically.

So I uninstalled the radio, swapped it, and brought it home. I looked inside the jack and didn't see anything out of the ordinary. Swapped a head from a good radio and tried one of my KMC-35s. Worked perfect. So I'll just hold onto it and use it for whatever.

Interestingly enough, our neighboring location brought some radios over for me to check and return, and I now have an NX-800H with the exact same issue. The difference with this one, though, is that I can see the damage inside the jack, and it's not pretty. One of the pins looks like it came dislodged, and there is a fair amount of corrosion and rust. Thankfully, I have a whole NX-800 (minus the chassis) we parted out, so I switched the head out, and now it works great. I'll try to post a pic of the damage.

 

[kenwoodgeek]

https://flic.kr/p/2h7Ps6Z

 

[n0fwg]

Without getting out a manual it looks like pin 7 the SW B+ line got eaten up.

Are your radios mounted verticly under the side wing window? Or somewhere during inclement weather it gets rained or snowed on, condensation from a window could also cause this.