Batboard

I have a UHF Portable GP300. The transitter part of the radio is great, but when you are recieving from this radio audio is good until you put up the audio and then it sounds like a helicopter coming in, it is very chopping only when you have the volume up to about 3/4's. When i plug in a speaker mic the audio is ok to turn up, but when i don't use a mic it like i said sounds like a helicopter coming in. Can anyone point me in the right direction.

Thanks in advance


John

On two GP 300's I have had I don't recall hearing a sound like that but more that the audio was very distorted but you could crank it up where it sounded more distorted. Yet when you used a speaker mic or headphones via the accessory jack the receive audio was clear and you could turn up the volume as high as possible without issues. The fix was a new internal speaker which was not that hard to replace.

Maybe there is more to it of course....

Sounds like the imfamous GP300 microphonics problem.
The speaker in the GP300 is vibrating the VCO coil causing the teribale audio sound. That is why with the external speaker the audio is good.

This is a known problem, the RX VCO coil is bad, and needs to be changed to the "purple coil".

I read other posts on this VCO problem and what Will said sounds more like the issue than what I came up with.

Just out of curiosity, what part(s) seen in the schematic are the ones you would replace - are they L250 and/or L268 that they discuss in the service manual in the VCO troubleshooting flowchart? The other posts do not make metion of the exact part/component numbers. And I see that you have to remove the VCO shield to get to those parts if they are the ones. I gather the shield is not an easy thing to unsolder.