SX-1010 won't come out of protection

ZeroJunk

AK Subscriber
Subscriber
I rebuilt the power supply board, usual suspects on the amplifier boards, recapped and replaced a couple of transistors on the protection board a few years ago.

Worked fine for a long time but it started dropping out a couple of weeks ago and now the relay does not engage at all.

The voltages on the protection board listed in the service manual are spot on.

But, power supply voltages have wandered a bit. Pins 10 and 14 are 60 volts,
15 is 27.5, 13 is 38, 11 is 24.95, 9 is 13.77

All seem a little high. Line voltage is 121 so it's not that.

Would 60 volts on the rail throw the protection circuit off ?

Any suggestions ?
 
q6 should be off then unless it is shorted .
try removing and testing q6 and also power on with q6 removed to see if relay clicks in then .
 
q6 should be off then unless it is shorted .
try removing and testing q6 and also power on with q6 removed to see if relay clicks in then .


All right, with Q6 out she comes out of protection just fine.

But, it does not show shorted. I have some KSC2383YTA's .
 
first check voltage at q7 base and pins 5 6 7 and 8 protect board and dc voltages at speaker terminals .
 
as a note it has been known for q1 or q2 protect board to go bad .. 0v q6 base pulling down q7 base seems odd to me .. by all means try a sub and see what happens .
 
first check voltage at q7 base and pins 5 6 7 and 8 protect board and dc voltages at speaker terminals .


Q7 base is 9.65 Not close to enough.
Pin 5 wanders between 1 and 2 mV
Pin 6 is around 12.2 mV
pin 7 16.5 mV
pin 8 -16.2 mV

No DC at speaker outputs
 
Hey Pete, Q 1,2,3,4 ,and 5 are all original. I only originally replaced Q6 and 7 .
I think I will replace them all and see what happens.

I'll report back one way or the other.
 
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