So I have 2 of these PSU's that have the same fault. Plug into bulb tester have 5v Stby present, no volts on PS-on pin in Stby.
When Ps-on is jumpered with resistor the bulb flashes 7 times in about 5 seconds and then goes dark. 4amp fuse does not blow. No 12 or 24 volts at all.
PFC circuit is still on at this point as it has 394 volts at input caps. All top and bottom diodes and resistors check OK.
So I removed Q903 the 2SK4101 N channel fet that drives the - side of transformer for 12 and 24 volts. Still flashes bulb.
Next I removed Q921 a STD1805a its a low voltage fast switching NPN power transistor. Bulb stops flashing but now no PFC. Caps at 164 volts. Transistor reads ok.
The emitter of Q921 is connected to Vcc of IC901 a Fan7529 a PFC controller. Which when on has fluctuating volt readings on VCC from 11.75 to 12.20 volts. The output fluctuates between .75 and 1.12 volts.
But it has to be ok since PFC is still active when Q921 is in circuit.
The PWM controller @ IC903 has 14v Vcc when PS-on is jumped, But it shows no output volts to Q903.
So I'm stumped from here, have been retesting all components just to make sure I did not miss something.
I cant get good pics of my own, it's raining here so I used one from SJ.
When Ps-on is jumpered with resistor the bulb flashes 7 times in about 5 seconds and then goes dark. 4amp fuse does not blow. No 12 or 24 volts at all.
PFC circuit is still on at this point as it has 394 volts at input caps. All top and bottom diodes and resistors check OK.
So I removed Q903 the 2SK4101 N channel fet that drives the - side of transformer for 12 and 24 volts. Still flashes bulb.
Next I removed Q921 a STD1805a its a low voltage fast switching NPN power transistor. Bulb stops flashing but now no PFC. Caps at 164 volts. Transistor reads ok.
The emitter of Q921 is connected to Vcc of IC901 a Fan7529 a PFC controller. Which when on has fluctuating volt readings on VCC from 11.75 to 12.20 volts. The output fluctuates between .75 and 1.12 volts.
But it has to be ok since PFC is still active when Q921 is in circuit.
The PWM controller @ IC903 has 14v Vcc when PS-on is jumped, But it shows no output volts to Q903.
So I'm stumped from here, have been retesting all components just to make sure I did not miss something.
I cant get good pics of my own, it's raining here so I used one from SJ.
Attached Files