Batboard

I have a 2 GP300 UHF 8ch radios that have little or no audio while transmitting thru the built in mic. It will work fine with a speaker mic or headset boom mic attached. I have changed the radio case (front assembly with spkr, mic, cable intact) with a known good front, still doesn't work. I have also used the suspect front case on a good radio and the audio works fine on it.
One of these radios was taken to a Moto dealer by the radio owner a couple months ago, and was told it would cost about $200 to fix. The second radio just started this same problem about a week ago. Both of these belong to a volunteer fire dept.

I suspected the mic jack causing problems, but I don't think it can be replaced. Can't locate a part number for it.

Anyone got any ideas???
Thanks.

The jack tends to be a high fail item on both receive and transmit audio problems. The part number for the jack is 01-80417C01. They run 14.25 list from circle m.

The switching contacts in the accessory jack gets dirty causing the loss of rx or tx audio. Cycle the jack severl times with a 2.5 and 3.5mm mono plugs to "clean" the contacts.
There are some service shops that will change the jacks for $40 to $75 plus parts needed. The accessory jack, and sometimes the RF contact and antenna test jack need to be changed as they have to be removed to get access to the accessory jack. I change the
accessory jacks on GP300, P110, P1225, Spirit
radios in my shop.