Help on Super Flower SFh750F14MG PSU

[cscs3]

Have above ATX power supply from a friend. Symptom is tripping home circuit breaker (however, internal fuse seem good).
1. Initial trouble shooting found input AC Live and Neutral lead is 0.02ohm. finally traced to FET Q301A shorted. It is a 5R199 N+channel FET. I replaced both Q301A and Q301B to 20N60C3.
2. Short circuit condition for input circuit is now fixed. However, the PSU still cause home breaker to tripped (fuse in PSU still good, quite surprised).

I failed to understand what else can cause a tripped to home breaker as clearly the current ahould be quite high and circuit breaker is fast to react to it vs fuse.

Do anyone happen to have a pointer on how to obtain a copy of circuit diagram for above power supply? It will be quite a waste to scrap away this nice power supply. So hope there is a chabce to have it fix.

[Per Hansson]

Re: Help on Super Flower SFh750F14MG PSU

A good start would be to use a 30w to 60w incandescent light bulb in series with the power supply:
If the bulb turns on the power supply is shorted...
Then you can go about trying to remove the short by taking components out of the circuit one by one.
But it really should be possible to see the short with a simple ohms meter.
Have you measured for shorts both before and after the bridge rectifier?
If so please test the four diodes in the bridge rectifier, probably one of them is shorted.

[CapLeaker]

Re: Help on Super Flower SFh750F14MG PSU

Check the gate drive of the mosfet. If the mosfet was shorted to the gate, full power went into the gate drive circuit. The gate drive could be stuck on.

I assume that the PSU trips the circuit breaker when you turn the psu on. With the psu off, it just sits there generating PSon?

[cscs3]

Re: Help on Super Flower SFh750F14MG PSU

Thank you for the replies and giving me the tips. Will Look into it and hope I have a good news to feedback here.

[cscs3]

Re: Help on Super Flower SFh750F14MG PSU

A good start would be to use a 30w to 60w incandescent light bulb in series with the power supply:
If the bulb turns on the power supply is shorted...
Then you can go about trying to remove the short by taking components out of the circuit one by one.
But it really should be possible to see the short with a simple ohms meter.
Have you measured for shorts both before and after the bridge rectifier?
If so please test the four diodes in the bridge rectifier, probably one of them is shorted.

Thanks for the tips.
Have tested the 4 diodes. Seem good. But will check again in case I missed.
Will also find a incandescent bulb before I do another test.

[cscs3]

Re: Help on Super Flower SFh750F14MG PSU

Check the gate drive of the mosfet. If the mosfet was shorted to the gate, full power went into the gate drive circuit. The gate drive could be stuck on.

I assume that the PSU trips the circuit breaker when you turn the psu on. With the psu off, it just sits there generating PSon?

Thanks, will do that. As I could not find a circuit diagram. Has to trace the printed circuit board manually. The circuit board is in black color. Kind of hard to trace actually.

[cscs3]

Re: Help on Super Flower SFh750F14MG PSU

Update.
Seem quit bad. The fillowing is in xircuit check. As these are surface mount componments and I do not have the specification of it. Seem quite impossible for me to repair it.
These are the componments around the FET thats is shorted.
R319D 1R0, believe is 1 ohm resistor. Open circuit.
D304 short circuit condition
D312 short circuit condition
D313 short circuit condition
D306 short circuit condition
Q303 and Q302 transistor/FET? short circuit condition. Not sure if due to above diode. (As I measured in circuit).
These are surface mount componments, so hard for me to identify the number printed on it.

[Per Hansson]

Re: Help on Super Flower SFh750F14MG PSU

Usually it is not that hard to disable the APFC and the power supply will then work at "medium" loads when your line voltage is 230VAC like it seems to be in Singapore.
(The bulk capacitor needs to charge to ca 400VDC for working with a full load, without it will be 230VAC x √2 = 325VDC)

I can't remember any threads off the top of my head now but try searching badcaps for that using Google, or the rest of the web and see what you come up with then write back if you have some questions.

[cscs3]

Re: Help on Super Flower SFh750F14MG PSU

Usually it is not that hard to disable the APFC and the power supply will then work at "medium" loads when your line voltage is 230VAC like it seems to be in Singapore.
(The bulk capacitor needs to charge to ca 400VDC for working with a full load, without it will be 230VAC x √2 = 325VDC)

I can't remember any threads off the top of my head now but try searching badcaps for that using Google, or the rest of the web and see what you come up with then write back if you have some questions.

Yes, I am from Singapore. Capacitor seem already 400v type. However, i am not sure how to do this modification. Probably will extract some useful components and scraps this power supply.

[Per Hansson]

Re: Help on Super Flower SFh750F14MG PSU

You can read this thread to get a general idea of what is involved:
https://www.badcaps.net/forum/showthread.php?t=107410

Here is another with a self-made schematic.
Basically you want the mains going straight from the bridge rectifier to the main capacitor, bypassing the APFC stuff.
https://www.eevblog.com/forum/repair...lar-schematic/

[cscs3]

Re: Help on Super Flower SFh750F14MG PSU

Thanks very much. Learnt alots here.