Low gain on one channel.
The DAC has been a puzzler, especially without a circuit diagram.
Inputs to U5 LF353 same size but outputs imbalanced.
Changing LF353 made no difference, the fault remained after changing and all the resistors around the LF353 seemed OK.
But I was getting weird readings around the pins either to Ground or to themselves. Wished I had a circuit so had to bite the bullet and do a complete blanket change of all the associated electrolytic capacitors, some of very dubious make!
The ones I decided to change were:-
C33 & C34 3.3uF 50V
C37 & C38 47uF 25V
C39 & C40 100uF 50V
C43 & C44 3.3uF 50V
C47 & C48 10uF 25V
C81 & C82 10uF 25V
I also removed the 8 pin socket which looked as though it could be contaminated, possibly chemicals from an electrolytic and thoroughly washed the board with iso-propyl alcohol.
I fitted a new 8 pin socket and the above new capacitors.
Second board wash after fitting everything and it now works well.
The NORMAL outputs are spot on but the tube outputs have a small imbalance, the Left out is -0.8dB down. I suspect the tube as the imbalance improves the longer the valve is run, possibly try replacing with a 5670.
The DAC has been a puzzler, especially without a circuit diagram.
Inputs to U5 LF353 same size but outputs imbalanced.
Changing LF353 made no difference, the fault remained after changing and all the resistors around the LF353 seemed OK.
But I was getting weird readings around the pins either to Ground or to themselves. Wished I had a circuit so had to bite the bullet and do a complete blanket change of all the associated electrolytic capacitors, some of very dubious make!
The ones I decided to change were:-
C33 & C34 3.3uF 50V
C37 & C38 47uF 25V
C39 & C40 100uF 50V
C43 & C44 3.3uF 50V
C47 & C48 10uF 25V
C81 & C82 10uF 25V
I also removed the 8 pin socket which looked as though it could be contaminated, possibly chemicals from an electrolytic and thoroughly washed the board with iso-propyl alcohol.
I fitted a new 8 pin socket and the above new capacitors.
Second board wash after fitting everything and it now works well.
The NORMAL outputs are spot on but the tube outputs have a small imbalance, the Left out is -0.8dB down. I suspect the tube as the imbalance improves the longer the valve is run, possibly try replacing with a 5670.