Galaxy Pluto problem

[eldorado303]

Hi guys. I just acquired Galaxy Saturn II ( SS3900F ) with some
issues. Some of them I've already solved. One that I havent been able to solve:
modulation is very low, and mic gain does not have any effect on the
modulation. I can turn it all the way down, and it still has modulation,
and all the way up is just the same. Modulation on AM is minimal,
and on SSB it goes up to 5 watts max, while the roger beep goes up to
25 watts. While I was trying to fix this, the brown lead came loose from
the mic connector ( inside the radio ), pin 1 ( ground ), and when I was testing the
modulation, it now had loud modulation, on AM, but with feedback, and
the mic gain now worked. On SSB, I had 25 watts, but with feedback.
I've looked at the schematic, and nothing else comes to mind. The mic
connector components seems ok. I havent tried switching mic's, but I dont
think this is a mic problem. What might be causing the mic gain to have
no effect on modulation? And what might be the cause of this low
modulation?

Thanks in advance,

Joao G.

 

[space cowboy]

did you test the mic gain pot?

 

[eldorado303]

did you test the mic gain pot?

Hi space cowboy. I hadnt before you asked, but had thought about it.
Now I have, and it's ok. I even bypassed the mic gain pot, and the audio
is still low. The roger beep sound ok though. On the radio's schematic diagram, you can see the modulation path, and the roger beep is directly fed to TR32, while AM modulation is fed to the AMC/ALC amp ( TR34 ). I've measured transistor voltages according to the voltage chart, and TR32 tests ok, while TR34 didnt seem ok.
Instead of the 7.8v, 0.6v, 8.3v ( B C E ), it tested 3.0v, 0.8v, and 0.8v ( BCE ).
I guess this one is not working correctly. I also tested more transistors,
and they all seemed ok. I'll try to fix it for a while more, if I can´t, I put it
on stand by. Any more ideias are welcome.

Thanks for your help,

Joao G.