I ordered a new RX filter before taking the 847 apart, hence the delay getting back with my fix. What I found was several loose screws on a couple of the boards in the 847. In fact the only screws that were consistently tight were the one's that I had removed/replaced when installing the Symec wide IF mod 5 years ago, I didn't open the bottom of the radio up at that time, so I don't know how long they may have been loose. After I buttoned up , all is now well, full duplex is back on FM. And I have much better RX on Ao-7 SSB, thanks to the 2.0 SSB Inrad filter ! It's about time I installed the filter, my 847 is over 8 years old. 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....
73 Jeff kb2m
----- Original Message ----- From: "Jeff Griffin" kb2m@comcast.net To: "amsat-bb" amsat-bb@amsat.org Sent: Monday, October 02, 2006 4:54 PM Subject: [amsat-bb] weird 847 behavior
I just noticed that when I'm working FM sats My d/l get's desenced, when I'm transmitting. This doesn't happen on SSB birds, only FM , and it just started. I also tried another Transceiver and the problem doesn't exist, I would think that would eliminate any problems with the antenna system, feedline, etc. Did anyone else ever have this problem with their 847?
73 Jeff kb2m
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
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Nate Duehr