the power supply is the switching regulator type, this chops the unregulated dc voltage (higher than 12v) on and off so that the voltage output regulates to 12v
ic301 pins 12/13 are open collector outputs that drives q302/q301 through r309/r305/r308
this output will be a high frequency pulse that chops the unregulated (higher than 12v) line on and off to generate the regulated 12v output
so you should see some sort of pulse waveform on pins 12/13, the voltage will probably should be higher than 12v when the output is OFF (voltage comes through the resistor chain) and drop to close to 0v when the output is ON
if however those output pins were shorted to gnd then the transistors would always be on and the full unregulated voltage would appear on the 12v output so check this too
ic301 pins 12/13 are open collector outputs that drives q302/q301 through r309/r305/r308
this output will be a high frequency pulse that chops the unregulated (higher than 12v) line on and off to generate the regulated 12v output
so you should see some sort of pulse waveform on pins 12/13, the voltage will probably should be higher than 12v when the output is OFF (voltage comes through the resistor chain) and drop to close to 0v when the output is ON
if however those output pins were shorted to gnd then the transistors would always be on and the full unregulated voltage would appear on the 12v output so check this too
Statistics: Posted by lovebug — Fri Jul 26, 2024 11:41 am