UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Yaesu FT736 internal mic gain adj possible?

orbanp1 · 2nd Dec 2019, 2:50 pm

Hi Richard,

I do not have a unit like that, but looking at the "FT-736R_Tech_supp.pdf" manual (from the Fox Tango International web-site), the block diagram (pg. 52-53) shows Q4002 and Q4003 as the mic amp stages for the FM mode.
Looking at the schematics, Q02 is an NPN transistor based amp stage, Q03 is an LM324 based amplifier stage for the mic circuit.
There is an adjusting pot from the output of Q02 to the input of Q03, it is part of the "MIC/DRIVE" pot assembly?, 10kA, on the "VR A UNIT".
It is marked VR03, though it is not clear if that pot is part of those other ganged pots. Is it part of an operating control?
It can be seen on pg. 50 of the Tech_support manual, in the "Connection Diagram".
There is also another pot, at the output of Q03(b), VR01, that sets the audio level for the VCO.
I would try to adjust those pots.
Just in case, mark the original positions of those pots, if the above note is off base.

Please note that this is just by looking at the manual.

Regards, Peter

2nd Dec 2019, 2:50 pm	#4
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: Yaesu FT736 internal mic gain adj possible? Hi Richard, I do not have a unit like that, but looking at the "FT-736R_Tech_supp.pdf" manual (from the Fox Tango International web-site), the block diagram (pg. 52-53) shows Q4002 and Q4003 as the mic amp stages for the FM mode. Looking at the schematics, Q02 is an NPN transistor based amp stage, Q03 is an LM324 based amplifier stage for the mic circuit. There is an adjusting pot from the output of Q02 to the input of Q03, it is part of the "MIC/DRIVE" pot assembly?, 10kA, on the "VR A UNIT". It is marked VR03, though it is not clear if that pot is part of those other ganged pots. Is it part of an operating control? It can be seen on pg. 50 of the Tech_support manual, in the "Connection Diagram". There is also another pot, at the output of Q03(b), VR01, that sets the audio level for the VCO. I would try to adjust those pots. Just in case, mark the original positions of those pots, if the above note is off base. Please note that this is just by looking at the manual. Regards, Peter