I have this amp in protection mode, its a Pioneer VSX-1021, the MCACC light is flashing. Service manual says it means DC on the output.
I pulled out the amp board and tested the transistors, found they were all ok, except for FL. I found the main power transistors are both shorted, and also the pre-driver stage same channel. All other transistor tested OK in circuit. I pulled the same transistors off SBL (Surround Back Left, its a 7.1 amp), thinking that would get left and right working, until I buy the replacements for the surround later. Left Surround channel left with no transistors in it.
Powered up and same problem again, protection mode. I dont know if the Left channel is working because its saying there are still DC issues. So I measured the DC on each output. Measured at the test points for biasing which are straight off the main transistor outputs, not the terminals on the back.
Now it gets weird, I get +60v on each channel (all 7 channels). I'd say this is not normal. I'm looking for advice on how to proceed from here, I'm thinking replace all the transistors on the board, all channels, and check all passive components.
Is this the best way forward or is there a better way?
Also, because the NPN transistors are on the positive rail, does that mean the +60v means each NPN is now shorted? Sounds reasonable to me but maybe its not that simple?
Thanks for any help anyone can give.
Cheers.
I pulled out the amp board and tested the transistors, found they were all ok, except for FL. I found the main power transistors are both shorted, and also the pre-driver stage same channel. All other transistor tested OK in circuit. I pulled the same transistors off SBL (Surround Back Left, its a 7.1 amp), thinking that would get left and right working, until I buy the replacements for the surround later. Left Surround channel left with no transistors in it.
Powered up and same problem again, protection mode. I dont know if the Left channel is working because its saying there are still DC issues. So I measured the DC on each output. Measured at the test points for biasing which are straight off the main transistor outputs, not the terminals on the back.
Now it gets weird, I get +60v on each channel (all 7 channels). I'd say this is not normal. I'm looking for advice on how to proceed from here, I'm thinking replace all the transistors on the board, all channels, and check all passive components.
Is this the best way forward or is there a better way?
Also, because the NPN transistors are on the positive rail, does that mean the +60v means each NPN is now shorted? Sounds reasonable to me but maybe its not that simple?
Thanks for any help anyone can give.
Cheers.
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