Cdm 1250 remote head

Have a cdm 1250 remote head radio programed it will recive but will not transmit on any channel programed in. Other radio I had done by the same guy that are not the remote head radio work fine. Would it possibly be the cable that runs between the head an base?

CDMs uses a serial bus (SB9600) to communicate between the brick and control head (most Motorola radios of the time did actually until being replaced by CANBus). I’d have to pull out a service manual on the CDM series radio to see if PTT was rolled into that control or if it was independent.

Does the radio beep at you when you hit PTT? Does the LED indicator switch from green to red?

Edit: The serial bus is officially called SBEP on the CDM series but I believe it to be the same as the SB9600 protocol. Yes, PTT is a logic low that is communicated to the micro-processor in the control head and then to the brick via the SBEP. (This info was located in the CDM Detailed Service Manual).

Have you attempted to swap microphones from the other radio? There is a PTT pin on the accessory connector but I don’t typically recommend accessing that testing without some care taken to not short out the audio pins.

You can hear it let the other radio but there is no voice sound. I did try another mic off my working radio an that never helped I was hoping that’s all it was.

Sorry. It keys the other radio but no voice comes across

It uses the Rkn4079a cable to connect the head to the base

Pointing towards either desense (transmitting radio is too close to the receive radio) or a bad TX audio line somewhere. Easiest way to test that would be to inject audio on the flat TX audio pins in the accessory connector and see if the radio will transmit then…takes some specialized equipment though.

Ok thanks I guess I will have to take it somewhere for it to be looked at