fsp 700w blows fuse when powered on

[techman2012]

hi can anyone help me out on which part i should check on what is shorted out or broken?


already replaced the fuse for the 1st time and
1. power on switch on psu socket = fuse ok
2. once psu is switched on via the power on 24 pin the fuse blows

here are some pics taken


what else do i need to check and how to diagnose

thanks in advance for your help

[mariushm]

Re: fsp 700w blows fuse when powered on

Post the images here as attachments. Click on Go Advanced and do it if you can no longer edit your post.

Anyway, the pictures are probably too low quality to figure out anything.

pics large size : http://img23.*************/img23/6877/img051lp.jpg and http://img341.*************/img341/489/img046rd.jpg

check the bridge rectifier - it's at the end of the long heatsink. Put the multimeter on diode check and test it (with power supply unplugged)

This video explains how if you don't know : http://www.youtube.com/watch?v=dqkT6hF0O3E

You don't have to remove it from the circuit. ps. actually you have two bridge rectifiers there, the ones marked with B. better desolder them both and test them outside the circuit.

[techman2012]

Re: fsp 700w blows fuse when powered on

noted currently removing the bridge rectifier

will post update in a while


thanks for the reply

[techman2012]

Re: fsp 700w blows fuse when powered on

both bridge rectifier are ok

[techman2012]

Re: fsp 700w blows fuse when powered on

currently checking the igbt removed the igbt 20n60c3

seems something is wrong which one is faulty here?

dmm set to diode
G C+lead E-neg lead
no reading

but if

G C- E+
i get a reading of 0.490v
one of the igbt when on these test gives out 0.007v

http://www.scribd.com/doc/49954768/20n60c3

as for the testing i watched this one

http://www.youtube.com/watch?v=AfV7gYChILc

[momaka]

Re: fsp 700w blows fuse when powered on

From what I can see, 20N60C3 is a MOSFET not IGBT, so the reading of 0.490 V you get when you put the (-) probe on C and (+) on E (that's actually D and S not C and E since it's a MOSFET) is normal.

I'm guessing this power supply is either a single or double forward design so check the DRC (diode, resistor, capacitor) snubber network. It's also possible that the high voltage bulk cap on the primary may be bad - there actually have been a few cases here on badcaps.net where people reported those CapXon high voltage caps failing.

To avoid blowing more fuses testing the power supply, once trick you can do is to wire an incandescent light bulb in series with the live wire going to the PSU. A 60W one is a good start. However, if you do that, you cannot connect a very large load to the power supply (i.e. you can't have it connected to a computer). The largest load you can have is maybe an old hard drive you don't care much about or a bunch of fans. If the light bulb becomes fully lit when you try to power on the power supply, the problem is still there. In that case, do NOT keep the power supply turned on for more than a few seconds to avoid burning out other components.

Also note that if the hard drive/fans use a lot of power, the light bulb may still remain somewhat lit. In that case, you can switch the light bulb to a higher wattage one. 100 to 150W should be plenty.

[techman2012]

Re: fsp 700w blows fuse when powered on

sorry my bad the one differs from the two everywhere i put probe the dmm beeps which means like shorted like when i put my probe + to - and it beeps

anyway ill try to find a 20n60c3 and replace the 3 of them to be on the safe side also will make that dim bulb tester

also if i will replace the capxon main cap
for ex:
320uf 600v original
can i replace it with
400uf 600v
or
320uf 650v?

also is it possible a main cap has problem thats why the mosfets got shorted out?

[tom66]

Re: fsp 700w blows fuse when powered on

What are the ratings on the cap? 330uF 450V?

[c_hegge]

Re: fsp 700w blows fuse when powered on

^
He said 320uF 600V. Using a 400uF and/or a 650V cap will be fine in an APFC circuit.

[techman2012]

Re: fsp 700w blows fuse when powered on

thanks c_hegge for the reply

[momaka]

Re: fsp 700w blows fuse when powered on

sorry my bad the one differs from the two everywhere i put probe the dmm beeps which means like shorted like when i put my probe + to - and it beeps

Yeah, that one is probably bad then. Just in case though, take it out of the PSU and check it again to make sure something else isn't bad either.

also if i will replace the capxon main cap
for ex:
320uf 600v original
can i replace it with
400uf 600v
or
320uf 650v?

Are you really sure the original is rated 600V? So far, I've only seen 400V and 450V rated ones.

[c_hegge]

Re: fsp 700w blows fuse when powered on

A close up look at the picture suggests it's actually a 470uF 400v

[techman2012]

Re: fsp 700w blows fuse when powered on

@momaka already removed all the straight heatsink to test the other one seems to be like a diode is ok besides the 3 20n60c3


as for the main caps later i will check it out for the exact values.



thanks all for the reply

will comeback for the result/update

[techman2012]

Re: fsp 700w blows fuse when powered on

main cap is 470uf 400v

btw here is the pic of the blown fuse before

[techman2012]

Re: fsp 700w blows fuse when powered on

already replaced the 3 mosfets and the main cap

made the bulb tester and its still a short since it lights up brightly

[budm]

Re: fsp 700w blows fuse when powered on

When MOSFET shorted out, especially between Gate and Drain, that high voltage will go through Drain, Gate, and the output drive pin of the SMPS IC to ground which will damage the output drive circuits of the SMPS IC. The bridge is OK? If the output pin of the IC stuck high, it will keep the MOSFET on instead of swithcing on/off, that will cause the MOSFET to draw a lot of current due to low DC resistance of the transformer, but if it is switching at high frequency as it should then the Reactive resistance of the transformer winding will be high which will limit the current through the transformer winding as designed.

[kaboom]

Re: fsp 700w blows fuse when powered on

When MOSFET shorted out, especially between Gate and Drain, that high voltage will go through Drain, Gate, and the output drive pin of the SMPS IC to ground which will damage the output drive circuits of the SMPS IC. The bridge is OK? If the output pin of the IC stuck high, it will keep the MOSFET on instead of swithcing on/off, that will cause the MOSFET to draw a lot of current due to low DC resistance of the transformer, but if it is switching at high frequency as it should then the Reactive resistance of the transformer winding will be high which will limit the current through the transformer winding as designed.

The three MOSFETs are strictly for the PFC-boost. There's some SMT stuff driving their gates on the back of the board.

The FETs avalanche when the cap dries out- energy stored in an inductor cannot disappear instantly. The current attempts to continue and a huge voltage is developed. When the cap is good, the current merely charges the cap...

[techman2012]

Re: fsp 700w blows fuse when powered on

so what do i do now? what do i need to check/how? thanks

[selldoor]

Re: fsp 700w blows fuse when powered on

When you have been removing replacing components have you been careful to replace any nylon/non conductive washers or sleeves if there were any.

[techman2012]

Re: fsp 700w blows fuse when powered on

When you have been removing replacing components have you been careful to replace any nylon/non conductive washers or sleeves if there were any.

yes im carefull when i removed and replaced the parts, there were no washer nor sleeves present.

after the test i havent checked if the replaced main cap or three fets have failed or not. will check it soon. btw while im testing it earlier with the bulb test, at first the light is dim then when i short green to black for psuon, the bulb glows full also the fan doesnt spin and i dont get any 12v/5v/3.3v reading . though it has a sound like a cap that is to bulge. but i didnt see any cap that bulge