• Need advice on two MOT Clean CAB radios.

  • Discussion related to railroad radio frequencies, railroad communication practices, equipment, and more.
Discussion related to railroad radio frequencies, railroad communication practices, equipment, and more.

Moderator: Aa3rt

  by howescf
Our Railroad, the Whitewater Valley in Connersville, IN, has been given two MOT CleanCab radios for use on our "newer equipment", SOO SD10 #532, and P&BR Baldwin S12 #346. Both radios have problems.

One has intermittant weak XMIT audio. Sometimes we all hear it loud and clear, sometimes we have to turn our radios up to hear it. I haven't found any cause / effect for this yet. Problem occurs / dissapears on its own, no matter whether using the handset or using the built-in mic.

The other occasionally HOWLS on receive. If I push the monitor button, it yields get a wonderfull white noise, just as you'd expect, but when it is actually receiving a signal, HOWL!!!.

Anyone have any suggestions where I should look in these rigs to find/fix the problems?

Chester Howes
  by clearblock
Are these units the older MCX/Syntor Clean cab radios or the newer Spectra's?

If it is a Spectra, I have found a common cause of intermittent problems is in the ribbon cables and connectors. The cable to the standard Spectra mobile chassis that is inside the Clean Cab housing and connects to the special RR control panel and interface boards can cause intermittent TX or RX audio problems or error codes. Check that the connector is well seated, the pins are not corroded and that there are no broken conductors at the bends in the ribbon cable.

I am not very familiar with the Clean Cab version of the MCX but I have seen a lot of regular MCX100s develop microphonic TX or RX audio due to trouble in the PLL circuit which could be the source of your howling. The intermittent TX audio could be a cable connector problem like I described for the Spectra or a cracked trace on the circuit board.

Both radios are miserable to troubleshoot at the component level if you do not have all the necessary adapter and test cables. I have seen reports of these radios having leaking electrolytic capacitors. If you have the radio open, it is a good idea to inspect for any suspicious looking capacitors before it fails or the leakage eats the trace off the circuit board.

Dick, K2HZ
  by howescf
Thanks for the reply Dick.

I'm "thinking" they are spectra, but don't know.

I'll open one up after I work my runs Saturday and take a look at cables, electrolitics, etc.


  by CarterB
I am a Motorola dealer. You can call Motorola repair direct at 800-927-2744 and ask for support. They will help you troubleshoot the Clean Cabs.
If you need more info, feel free to email me.