STK-0039 board voltages question

[Mike Mag]

I am repairing an SA-300 receiver
I have pulled both 0039 modules and they are bad
I have replaced two pre-driver transistors
I have verified all capacitors in DC path are good

here are the voltages I measure and although I have done as much reading as possible on this I still am a bit unsure if all is good to install new modules

these are the voltages without the modules installed and phono input selected, volume at zero

1) -37.6V
2) -38.0V
9) +37.8V
10 +36.0V

both channels read the same

so my question is: is one of those voltages wrong and will blow the modules when installed ?

 

[sregor]

To test amp without stk0039, you need to add 220 resistors between where pins 0 and 8 would go, and between pins 1 and 3. There is no path for feedback without a module or a resistor, and the output floats towards the rails, which causes protection circuit to not turn on, and useless measurements. If everything is good, you should get zero volts at the output, and about a volt on pin 10 (or pin 0) and about -1 volts on pin 1, near zero volts on pins 3 and 8. Pins 2 and 9 are the minus and plus power supplies.

 

[Mike Mag]

To test amp without stk0039, you need to add 220 resistors between where pins 0 and 8 would go, and between pins 1 and 3. There is no path for feedback without a module or a resistor, and the output floats towards the rails, which causes protection circuit to not turn on, and useless measurements. If everything is good, you should get zero volts at the output, and about a volt on pin 10 (or pin 0) and about -1 volts on pin 1, near zero volts on pins 3 and 8. Pins 2 and 9 are the minus and plus power supplies.

What wattage rating should the 220 ohm resistors be ?

 

[sregor]

What wattage rating should the 220 ohm resistors be ?
Half watt is fine. Don't connect speakers or load, but you can run a signal and look at the output on a scope.

 

[Tom B]

I am repairing an SA-300 receiver
I have pulled both 0039 modules and they are bad
I have replaced two pre-driver transistors
I have verified all capacitors in DC path are good

here are the voltages I measure and although I have done as much reading as possible on this I still am a bit unsure if all is good to install new modules

these are the voltages without the modules installed and phono input selected, volume at zero

1) -37.6V
2) -38.0V
9) +37.8V
10 +36.0V

both channels read the same

so my question is: is one of those voltages wrong and will blow the modules when installed ?

How did you confirm the originals were bad (short between pin 8 and 9, and/or pin 2 and 3). or was it blowing fuses, or having high DC at output?

 

[Mike Mag]

using Steves advice I was able to confirm operation and the SA-300 is back in operation

 

[Mike Mag]

How did you confirm the originals were bad (short between pin 8 and 9, and/or pin 2 and 3). or was it blowing fuses, or having high DC at output?

I confirmed the old modules were bad as well as the two differential transistors. I have replaced all and the set is running