ALC and audio Tx problem


Peter Hewitson
 

Thanks for the very detailed explanation. I will see what I can do. 73, Peter
 


 

I had this problem with one of my IC-7000s. My symptoms were full ALC on SSB and 100% + output on all other modes.
Turning the power down has no effect.
The ALC circuit gets one input from the SSB logic on the UNSB line to the Q1606 FET that changes the ALC bias.
In my case the FET was bad it I recall correctly. What happened was the voltage on the line that gose to the op-amps was low (?). What happened was Q1606 shorted and the two 2.2 meg (series R1641 & 1636) were always pulled low and did not change when switched to SSB mode by that signal from the NUSB line. if I remember correctly it is high when not in USB. 
Your mileage may vary.
I have attached a copy of the schematic for this part of the circuit.
IC1601 are the op-amps that vary the ALC bias to control power and fold back due to SWR etc.


Peter Hewitson
 

On Tx, ALC is full scale on all modes but no output on SSB. Transmits on CW and AM but still getting full scale ALC on meter. Any clues? Thanks Peter