Sunfire no + down convertor power


New member
Username: Frodo_ballings

Post Number: 1
Registered: Aug-13
Dear all,
I join this forum because I have a Sunfire in repair and there is something I do not grasp in the schematic I downloaded from the Carver website.
This thread was very helpfull and all that could be bad was bad : the powerstage transistors, some FETs, the 4 biassing diodes and of course the 2 jumpers JP1 and JP2. The glass fuses were OK ...
After replacing the lot, the "+ down-convertor" does not work.
For testing the low-voltage part, I disconnected the small transformer from the big powertrafo secondairy. That way, there is no danger blowing it all up again.
My question : How is the circuit for the + down-convertor FETs powered (Opto U1, Q8&Q9) ?
I see the diode D5 giving +13V as powersupply but where can it source current to ?
The "ground" circuit is connected to the sources of the FETs Q22/23/24 and at that point the voltage will most of the time be higer than +13 V . . .
Has anybody reverce-engineered that part of the system ?
Anyway, if I measure the voltage over zener Z3, I get next to nothing (0.3V) altough the +13 V is OK.

Thanks for your enlightment !
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