GM300 Receive Audio Howl

W7SLC · Post by **W7SLC** » Wed Sep 26, 2001 5:19 pm

My recently purchased GM300 (UHF Hi Power 16 Ch) has what sounds like receive audio feedback. When I unkey the mike the rx is ok until near the repeater squelch tail with the volume turned up, as the repeater drops, the internal speaker begins to howl and sometimes continues after the repeater drops for 10 sec or so. Is this normal or is this a known problem with a known fix.

Thanks..Neil

jim · Post by **jim** » Wed Sep 26, 2001 6:30 pm

This is called "microphonics" and is a common problem on these radios. It may be as simple as one of the tin RF shields inside the radio being loose or corroded. It may be the VCO circuit, which is also common. Usually, it is a loose component or coil on the board. If you're not that experienced inside of these radios, take it apart and unplug and re-plug evenrything inside. Remove and re-install the tin shields covering the critical circuits then retry the radio. If the problem persists, see your local "M" dealer.

Reslock · Post by **Reslock** » Wed Sep 26, 2001 8:07 pm

That radio is definitly microphonic. Disassemble it down to the p.a. and the chassis. Then, use and eraser to clean all the pins that go through the chassis. wipe them down sparingly with a contact cleaner or WD-40. That will fix it.

W7SLC · Post by **W7SLC** » Thu Sep 27, 2001 1:22 pm

Thanks very much for the info. I will try it out over the weekend. Its a great radio otherwise.

Neil

Doug · Post by **Doug** » Thu Sep 27, 2001 2:36 pm

What they say is true the ones that I've owned I've been lucky enough to correct it just by making sure the screws on the boards were tight.
Doug

W7SLC · Post by **W7SLC** » Sat Sep 29, 2001 7:11 pm

It Worked!!! There were several screws that were quite loose inside the radio which was otherwise very clean. I retorqued them and the problem is gone.

Thanks for the great advice!

Neil