FT-991A Intermittent and fading audio in internal speaker

There's a number of reports in FT-991/A communities over the internet informing about a FT-991A issue where the internal speaker audio starts to fade away, going lower and even completely muted. If you crank up the volume, the audio returns back again but the issue will return again.

This issue does not happens in front PHONES jack or in rear EXT SPKR port.

Resolution

Fortunately, it is a easy fix. Insert and remove the plug in the rear EXT SPKR port (say, some 10 to 20 times) in order to try to wipe the small switch inside the speaker jack. If you have canned air, give it a blow in the EXT SPKR port. To understand why; keep reading.

Root Cause

The culprit can be dust build-up or corrosion in the small switch that exists in the EXT SPKR jack. See the below schematic:

1. The audio signal comes through the blue line, and enters the RL1002 - that's the relay that mutes your radio when you quickly press the on/off button, to avoid a loud pop/bang when turning the radio on or off, by diverting the audio signal to ground (green line).

2. During the normal operation, the audio is outputted in the purple line - and starts a trip to the Jack Unit.

3. At the Jack Unit, the incoming signal signal (purple line) goes to the front PHONES jack. If there is nothing connected to this jack, the audio signal travels back to the Main Unit, via the pink line. NOTICE the purple square: The signal back to to the main unit depends on the electrical integrity of the internal switch in the jack.

4. Back to main unit again, since you did not have something plugged at the front PHONES jack, the audio signal returns to the main unit via the pink SP signal and goes to the EXT SPKR jack, at the rear side. Notice again the pink square, pretty much the same as the previous item: The audio being forwarded to the next step depends on this electrical connection integrity. It is this point that usually causes problem.

5. IF there's nothing connected to the External Speaker port, then finally the audio is sent to the Internal Speaker, over the orange line.

Troubleshooting steps

i. In order to isolate the problem, start with the External Speaker. If the external speaker works just fine, the problem is at the EXT SPKR jack. Blow air (use compressed air, do not use your breathe) and do a number of plug insert/remove to try to wipe the internal switch.

ii. If the External Speaker also presents the audio fading, repeat this tentative cleaning process procedure in the front PHONES jack.

iii. If it still does not help; it is something else - look for an experienced technician or Yaesu maintenance.

Hope that helps - 73s de PY2RAF.

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