Jeff Griffin wrote:
So it appears the fix was a loose semi-grounded board, most notably the AF-CNTL unit board. Thanks to everyone that emailed me privately with their suggestions....
I'd be interested in what you heard about various ideas. I have an FT-847 that any time a mic that draws power for features (i.e. DTMF mic) is used, a noticeable but light hum is introduced in the transmitted audio.
Yaesu took a look at it and replaced a cap in the power supply section, but it didn't fix the problem. (And cost $90... what a waste sending things to Yaesu is these days... apparently they don't look at anything on a service monitor before sending it back.)
One of the "common" failures in the FT-847 appears to be bad grounds from loose boards inside. I may have to open mine up and check that out, if I can ever make the time to do it. Maybe it'll end up on my checklist for radio maintenance annually -- just open the thing up and tighten everything. Maybe a mod to ensure proper board to board grounding...
Always something to do... the FT-847 problem isn't high on my list because it's easy to avoid (using the stock mic or a Heil headset, the problem doesn't exist, using any mic with power draw it does... quite odd, but at least it's nailed down to a particular circuit... better than SOME troubleshooting "fun" I've had over the years).
Nate WY0X