ntropic wrote:Must have missed the bit about C7/C16. They both measure 0.959-0.961V.
Seems a bit low, which could explain why you're not able to achieve the desired quiescent current.
Q5/18 and Q8/21 check out.
Q4/17 fail +C/-E test, pass +B/-E test.
This is fine, because these junctions are explicitly shorted (see the schematic, and the BJT sanity check doc also mentions this).
Q8/21 fail -C/+E test.
Hmm, you said above that Q8/21 passed? So which is it.
Q9/22 both fail -B/+C/+E tests. Abnormal voltage in +B/-C/-E test (0.3/0.5V).
This may be ok because of interaction from resistors R12/13 R36/37.
Q10/23 both fail -B/+C, but not -B/+E. Normal voltage in +B/-C/-E test.
Q9/22 and C10/23 fail the +C/-E and -C/+E tests.
You already mentioned Q9/22, but Q10/23 looks suspicious.
Q6/19 check out.
Q1/14 fail -C/+E test, pass -B/+E test.
Same comment as Q4/17 above.
Q11/24 fail +C/-E and -C/+E tests.
Q11/24 fail +B/-E test, but not +B/-C. Normal voltage in -B/+C/+E test.
This doesn't seem right either.
Q7/21 fail +C/-E test. Normal voltage in -B/+C/+E test.
The right channel version of Q7 is Q20, not Q21. Q21 is NPN. I assume this is just a typo and you really meant Q20. This doesn't seem right either.
What about Q12/25 and Q13/26?
Double check again that you don't have BC550C and BC560Cs mixed up on the board, and the output transistors too (are they swapped, or installed backwards). If an amp doesn't work af initial setuip time, and both channels exhibit the same problems, it is likely that you assembled the two channels at the same time and made a repetitious mistake somewhere on the board. This may
have caused some of the transistors to be damaged, but check the board very carefully first.