2330B Driver board dilemma.

[tutor_turtle]

I have 2330B in for blown outputs.
The customer was driving two 4Ω speakers and fried the driver board.
I identified the many, many damaged parts.. Some transistors are unavailable so I used the recommended On-Semi replacements.
I even managed source original output transistors.
I could not get the bias to budge from zero. I read on posts here the bias control transistor Q738 (2SC1953) was a critical component that the replacements sometimes didn't work.
I managed to source an original 2SA1953, he also had original 2SA913 and 2SC1913, which were the only other parts that were not OEM.
It worked, it biased... at least for a few minutes then the bias started running away, before I could power it down I heard a snap!
Q736 (2SA914) shorted and took out a number of resistors with it.
I used the KSA1381 replacement. That part is now running red hot, bias is stuck at -12mv.
I've unsoldered and tested every part on the board. The board traces have gotten pretty beat up with all the rework, it is possible I have some fractured traces.
Art this point without a donor board or a new blank card, I think I've hit a dead end.
Any input would be appreciated.

 

[pat2330b]

Hi considering that the p700 board is in bad shape i would strat the projet rebuilt with a new board.
https://www.cafr.ebay.ca/itm/284046118095

put new resistors, keep the same coils (if ok) new caps and find transistors équivalence. Choose little higher voltage, A and respect lower to higher frequency from output to differential in transistors replacement selection. try to get close of originals gains too. (always higher)

 

[ivandezande]

I've had the same problem, bought that board, and still couldn't get it going. Fixing 2330B's is a time suck.

 

[mbz]

Replace all suspect parts then DBT power up and monitor bias for stability for say 30min. Check for excessive heat on those previously failed R's and TR's. Check voltages (Vdc) at bias transistor collector then emitter (+/-1.2Vdc??).
DBT should be dim all this time.

Note VR position, attempt slight adjustment of bias (while on DBT), expect bias responds to VR adjustment, restore VR to previous/minimum bias position. Decide if ok to power up without DBT.