188362 Schematic

Many switching supplies have a startup resistor (high value, 100k-470kΩ) from the main DC bus to the VCC pin of the PWM IC. Once running, an auxiliary winding on the transformer takes over. If this resistor is open, the IC never starts.

Using your DMM in diode mode:

Since we are dealing with a standard identifier, let’s construct a representative schematic block diagram. If you have a physical board, use the following guide to match your hardware. 188362 schematic