Continuing the story
I am still looking inside the PA. This rig was bought in 1987 from a store when it closed, and might have had a previous owner.
Today I found a modification not documented anywhere (as far as I know). I mean modification because it can be seen the place in the PC where components were before, choke L05 in PA cut from original place (13.5V), and moved to TX13.5V.
The predriver Q01 takes now collector voltage from TX13.5V line, that is the bias (TX ON) voltage. There is another 13.5V line for driver's collector. That is a mod. In the manual the prediver and drivers take voltage from 13.5V all the time. TX13.5 in only live when "transmision and HAM and not transverter used". 3 conditions. The logic is in RF unit.?
So before I start cutting tantalums, I better look at Q01. BTW it is not thermal connected, the screw has never been there.
The fact that Q01 takes power from TX13.5V instead 13.5V may have consequences because for base bias not much intensity is needed, but for Q01, I guess maybe 200mA are needed. I dont know because this mod was done or who did it. Maybe self oscillation, because same mica capacitors around output coils seem a bit toasted.
In short, a new protagonist, Q01 missing the thermal connection it never had, but should have had. I was centered in capacitors, or any of the two cascaded TX ON regulators (BIAS), from 12.5V to 0.7V. ?
73 EA1FC
