Batboard

I have a GP300 UHF radio with bad receive audio. The audio sputters at any level on internal speaker and it sputters at 1/2 volume or more on external speaker/mic. What causes this?

Can you define 'sputtering' a little better? If it's what I think you mean, you're saying that the squelch is opening and closing randomly - is this correct? The GP300 design never had good squelch hysteresis. At low RF input levels between 0.14 and 0.20 uV RF input on channel on most GP300s, I've found that the squelch action is not positive(i.e. "open" or "closed") like it is on other portables in Motorola's line. However if you mean that squelch is randomly opening and closing when the RF input level is >0.30 uV or greater, then I would say you have a definite squelch circuit problem or receiver front-end problem. What's the 12 dB sinad number look like? If it's in the 0.2-0.3 uV range, then I'd look at the squelch circuit. If not, then I'd look at the receiver's front end.

Hello Al. This is a sputtering, not a squelch open and closed chop. Problem is now solved. Bare circuit board with external power and speaker worked OK. Shield and heat sink installed on board and housing speaker plugged in was OK. When everything was installed back in GP housing the sputtering started again. I found that the internal speaker frame was shorted to the speaker voice coil. The frame is grounded to shield when all is assembled. A new speaker solved the problem.