Batboard

I have a CDM1550 VHF (non-LS) AAM25KKF9AA5AN. It is recently acquired. It reads and writes fine, transmits and receives fine. The problem is when I plug it in the heat sink gets hot, even when not transmitting. Any ideas?

I have never seen this before.

Probably a failed or failing PA transistor.

If there is anything connected to the accessory connector, make sure that none of the speaker output pins are grounded. I had a bus radio do that do me on a swap out one time, the speaker they already had was grounded.

Is it a remote mount? If it is, open the head, and put some insulation between the circuit board and speaker terminals. A couple layers of electrical tape should do. In the remote mount kit they put an exposed ground pad on the board right under where the speaker terminals are and there is not much clearance so it shorts and causes the radio to get very hot, eventually killing the radio.