SX-950 Relay Bypassed and Burnt Resistors

Replaced 2sa733 with a KSA992.. No relay click

Q5 KSA992
B= 13.4v
C= .245v
E= 14.1v

Q6 KSA2383YTA
B= .243v
C= 1.99v
E= 0

Q7 (this readings are jumping around plus or minus 1 volt.
B= 1.8v
C= 26.5v
E= 1.26v
 
Your Q5 base voltage needs to be higher than the emitter voltage in order to turn Q5 off. Q5 emitter should be just a little more than 1/2 of the Pin 11 voltage.
 
I pulled all the zeners from the protection board this morning, and all tested between .560 - .690. and OL'ed when swapping polarity.
 
D6&7 aren't suspects but lifting one end isolates Q3&4 collectors from the base of Q5.
 
I put a 75W bulb in the DBT and the relay is clicking! :beerchug:
Didn't leave it running very long tho.. Worried its going to smoke again
 
now its clicking you can check dc offsets at speaker terminals to see if it got better than it was before . seem to remember it was a little high .
 
Both left and right are at .09v
I had installed the new multi-turn pots, and turning them down doesn't lower the voltage anymore than .08-09v
 
i wouldn't think the outputs installed would make it any better but might do .. did you replace q1 q3 q2 q4 with matched pairs ?
 
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Yes.. I went through and found matching pairs by recording hFE with component checker. then retested again.
Is that correct method?
 
yes correct .
you could try even higher wattage lamp or go to full mains and check again . just to rule that out . at least you would know its safe to put a pair of outputs in to test on lower wattage dbt .
 
So installed a 100W bulb, DC offset came down 0.06-.07v

Went full main power and that brought it down to .05-.06v
 
thinking try just one of outputs into one channel ..idle bias pot would first be best turned to min for this .
example ... just install say q13 q15 ...hope i got the 13 right as this schem is not legible in places ..
 
Agreed.
I will start working on this process tomorrow. We made good progress so far and nothing let the smoke out this time!

Thanks for your help Pete!
 
Ok.. umm...
What schematic in the service manual can I look at to see which OP transistor is which?
I'm not seeing Q13 or any callouts for the output transistors other then P/N designation
 
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