17PW16.2 Blowing Mains Fuse But Nothing S/C

[ReeceyBurger123]

Unsure what is causing this, checked most of the parts I will list what I checked. There is no ohms between the live and neutral terminals which probably means there is no short on the input side (normally) and nothing on the output is shorted. Fuse explodes very fast as soon as power is applied. Any ideas chaps ?

Tested so far for ohms non test S/C or O/C even leaky:

Q814
Q813
Q803
Q809
Q840
Q839
D824
D866
D846
D845
Ac rectifier
All ac input components
Ic806
Ic802
Ic807
Ic825
Ic828
Ic809 (opto)
Ic811 (opto)
Ic801 (opto)
R830
C920
C819


All parts listed are common failures on these but all are good. I literally cantfind what is causing this. Any ideas are appreciated.

[dick_barton]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

An exploding fuse is definitely a sign of a major short circuit. Surely it should show up as a s/c on your meter. Has a diode gone down in the bridge rectifier?

[multimeter]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

psu pic? main filter cap checked for short?

[ReeceyBurger123]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

psu pic? main filter cap checked for short?

I have checked the Pfc cap for Esr and its fine, little high but will be ok. Here is an image:

[ReeceyBurger123]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

An exploding fuse is definitely a sign of a major short circuit. Surely it should show up as a s/c on your meter. Has a diode gone down in the bridge rectifier?

I have checked the Ac rectifier it tests fine in all directions.

[budm]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

Test in Ohm mode, so the two inner pins of the bridge show high resistance? The two outer pins of the Bridge show high resistance?
You should put lamp in place of the fuse so you will not keep blowing new fuse, run the board by itself and if the lamp glows brightly and stays on bright you still have shorted circuit.

[ReeceyBurger123]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

Sorry bud I didnt phrase that properly, the bridge diode tests fine. Every diode in it tests normal as they should for an Ac rectifier. Also thanks for the schematic will have a mess with it see if I can find anything down the line bad

[multimeter]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

cant see properly but does it have a FAN*** 8 legged IC ?,if so check vcc to ground for low ohms

[dick_barton]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

How about leakage from Live to Earth, Neutral to Earth?

[ReeceyBurger123]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

cant see properly but does it have a FAN*** 8 legged IC ?,if so check vcc to ground for low ohms

Yes I have checked the Fan Pfc control Ic on all pins to ground, I should have labelled everything in the description. The Pfc Ic tests fine normally that only blows if the Pfc fet shorts which it is not.

[ReeceyBurger123]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

How about leakage from Live to Earth, Neutral to Earth?

Live to earth:
No ohms

Neutral to earth:
No ohms

Live to neutral:
No ohms

[multimeter]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

if you have checked all the usual suspects,unusual, but could be shorted SMPT

[Alastair E]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

By side of pfc transformer between it and heatsink near transistor monting-bolts and somewhat hidden--1000pf cap...

[ReeceyBurger123]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

Image of underside of Psu:

[budm]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

Got be overlooking something, for the fuse to explode it will be the PFC MOSFET or the bridge, IC806, the two MOSFETS for the 24V SMPS are in series (1/2 Bridge drive setup) so both of them have to be blown. What was the history on this supply, some one work on it before you? Disconnect the two outer pin and see if the fuse is still blowing.

[ReeceyBurger123]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

By side of pfc transformer between it and heatsink near transistor monting-bolts and somewhat hidden--1000pf cap...

Checked that bud as stated, I should have bloody lablled everything lol

[ReeceyBurger123]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

Got be overloking something, for the fuse to explode it will be the PFC MOSFET or the bridge. What was the history on this supply, some one work on it before you? Disconnect the two outer pin and see if the fuse is still blowing.

Thats a good idea, will do tomorrow Bud.

[Alastair E]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

pfc inductor itself...?

[Alastair E]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

To save dosh on fuses--wire 100W bulb in place of it!

[Brighton Mike]

Re: 17PW16.2 Blowing Mains Fuse But Nothing S/C

Is a diagram available?