Another Ross Comp Debug...yay!!!

[ppatchmods]

thanks Mike. i went to harbor freight and picked up a nice headset magnifier with led's for 10 bones, so i'm gonna give it a workout tonight.

[ppatchmods]

all components checkout and are in the right place. i have seriously spent about 10-15hrs trying to debug this thing.

what does it mean when the voltage readings on the E & B of q5 start at one point and slowly move up/down? the E starts at about 7.25 and moves up to 8.45ish and the B starts at 8.21 and moves to 7.75.  the only thing between pin5 and the E of q5 is the 27k and the pot. i have changed both out and get the same .06 reading......thinking about starting over

[Toney]

question: is the voltage to pin5 affected only by r21 (27k) or does the sustain pot have a big affect on it?

also, would the sustain pot have an affect on q5 or does q5 affect the sustain pot?

i'm pretty sure that q5 is my problem. i replaced it with a 3904 and got the same readings.

I would spend my time carefully checking the components around Q5, Q3 and Q4 the Sustain pot itself (wiring, value) and then on to the CA3080 they can all directly affect Q5.
Are the diodes off Q3 and Q4 correctly orientated?
Also, do you know for sure the CA3080 is good? I think you mentioned something about having build a few of these. If they are in sockets can you plug this one in to check?
Remember: solder bridges, component values and wiring issues are probably 1, 2 and 3 in Vero debug !
Sometimes taking a break is the best choice.
Many times I have cracked it, come back and just seen the problem jumping out at me.

[Toney]

 
Oh yes, to answer your question, absolutely!
It is connected to the emitter of Q5 and with R21 (27K resistor) is directly part of the bias.
I would also do a very careful check for bridges/shorts between all the tracks around the CA3080