[1000mp] strange speaker problem

[FireBrick]

Using a ft1000mp and have a Yaesu SP8 speaker.(that's the version with the built in audio 
filtering which I never use)
I don't use the speaker that much preferring earphones on cw and ssb.
but occasionally use the speaker.

Here's the problem. When I pull the headphone plug out of the MP, there is no sound coming 
out of the SP8.
Not EVERY time, but most of the time.
But if I turn the audio gain on the MP, it pops back to life, way too loud.
I can then turn the audio gain on the MP back down to a normal level.
And sometimes, the sound will quit if I bump the desk.
Tapping the SP8 case will 'sometimes' bring it back.
But turning the AF gain on the MP works EVERY time.

Sort of like a circuit is tuned too close.
Changing the settings of the SP8 filtering does cause changes in the filtering but does 
not effect the muted audio until gain reaches some threshold situation.

I've checked all jacks and wiring for cold solder joints.
The SP8 is connected to the SPK jack on the back of the MP of course and is disconnected 
when using headphones.

So before I try and bypass the audio filter circuit, can anyone make a suggestion.


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