If you are trying to debug whether your PL amp problem is on the backplane side of things or on the PL14 control board and wish to do that without blowing fuses or damaging output transistors, this debug trick may help you perform the debug without causing further damage.
After you have determined that the output stage is off with the wires to pins 3 (violet) and 9 (blue) disconnected and tied off (yes the real pin 3 and 9 J) and with a 1K resistor across each output speaker post you get near zero volts across that resistor (should be less than 10mV).
Also disconnect and tape off the wire to pin 4 temporarily.
With wires to 3 and 9 disconnected, tack solder a temporary 1K 1/2W resistor from pin 9 to pin 6. Tack solder a temporary 100 ohm 1/2W resistor from pin 3 to pin 12. Tack solder a temporary 1K 1/2W resistor from pin 4 to pin 6.
This should work like a mini power amp with not much danger of blowing stuff up. It will not drive a speaker load, this is just for debug.
Use the original PL schematic to debug your problems.
Once you have this working perfectly then you can disconnect the temporary tack resistors and reconnect the wires you temporarily removed.
After you have determined that the output stage is off with the wires to pins 3 (violet) and 9 (blue) disconnected and tied off (yes the real pin 3 and 9 J) and with a 1K resistor across each output speaker post you get near zero volts across that resistor (should be less than 10mV).
Also disconnect and tape off the wire to pin 4 temporarily.
With wires to 3 and 9 disconnected, tack solder a temporary 1K 1/2W resistor from pin 9 to pin 6. Tack solder a temporary 100 ohm 1/2W resistor from pin 3 to pin 12. Tack solder a temporary 1K 1/2W resistor from pin 4 to pin 6.
This should work like a mini power amp with not much danger of blowing stuff up. It will not drive a speaker load, this is just for debug.
Use the original PL schematic to debug your problems.
Once you have this working perfectly then you can disconnect the temporary tack resistors and reconnect the wires you temporarily removed.
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