I would beg to differ regarding an internal pot for the mike gain on the tmv7a.
If there are any internal pots at all, they control other functions.  The audio 
gain, both receive and transmit are both controlled by the micro processor and 
not controlled by an analog device.  For instance when you use the microphone 
remote control feature, and use the volume and squelch adjustment buttons, the 
radio adjusts those functions, and as soon as you go to adjust them again on 
the radio, it will default back to what ever it was before you started 
adjusting from the microphone.  If there was an internal pot that controlled 
either audio or squelch, this could not be accomplished the way it is.  The 
same holds true for the tx audio.  Since there is an option within the service 
menu to adjust the tx audio, it wouldn't then also have an internal pot to 
adjust since the internal processor is already controlling that function nicely.
There are likely surface mount components that could be altered to adjust the 
gain, in other words, the various information being sent to the processor.
73
Colin, V A6BKX