Switching Power Supply Startup Circuit Problem?

I'm repairing a Switching Power Supply. It has HIGH voltage DC circuit @ 320VDC. There are two "chopper" supplies. The 12VDC is the primary output. The 20VDC is for the chopper circuit, a TL494 chip. All semi test fine with Ohm meter. There is no Vcc on the TL494 when plugged in so the chopper... show more I'm repairing a Switching Power Supply. It has HIGH voltage DC circuit @ 320VDC. There are two "chopper" supplies. The 12VDC is the primary output. The 20VDC is for the chopper circuit, a TL494 chip. All semi test fine with Ohm meter. There is no Vcc on the TL494 when plugged in so the chopper never runs. I can "jumpstart" the TL494 by momentarily applying external 9VDC to Vcc and Grnd. Supply runs fine w/o battery after that until unplugged.
Brand: HANNY Model: FX-101
No schematic or tech support available. The problem is the initial startup. How does HANNY design the startup for their switching supplies? Is it a mini linear supply? A starting resistor? A starting cap? Self resonance? What do I look for? Checked power resistors, all in spec. What can I look for? Supply is only five months old, likely not dried caps. Ideas?
3 answers 3