Polaroid FLM-2601 - Power Supply keeps blowing fuse

[drpj23]

So I have gone through 3 fuses on this thing. The fuse blows as soon as there is AC going through it.

I know this board is notorious for failure so hopefully someone has some insight. I know the board is noticed for the capacitors failing but I don't believe this the case (at least yet lol)

I know on power supplies this can be caused by bad diodes. Is that what I should shoot for? Or look at the bridge rectifier? Or....?

[budm]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

Can we get more in focus pictures, especially the bottom side, we are trying to troubleshoot it from long distant, good pictures are a must.
I can see the bridge rectifier around top left of the board.

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

Yes, give me a minute.

[retiredcaps]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

I know on power supplies this can be caused by bad diodes. Is that what I should shoot for? Or look at the bridge rectifier? Or....?

Likely suspects are

a) bridge rectifier is shorted
b) power mosfet is shorted (it maybe Q903)

[budm]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

Here is what inside the bridge rectifier for you to check. You know how to use the meter well?
This power supply has PFC circuits also.

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

Here are some better ones.

The underside is as if I rotated it and flipped it.

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

I'm pretty familiar with one.
For this, I would measure pins 1 and 2 in both directions and if there is low resistance in both directions it is bad or if there is no reading at all it is bad
and likewise for pins 3 and 4.
Right?

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

And yes there are two mosfets on the board (V906 and V907 (in this case)). I'll prob take those out and check them too.

[budm]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

OK, please see the attachment, we are going to check the bridge first.
Tell us what you read with the Ohm meter setting to 200 Ohm scale (notes: since we are looking for short circuit that is bad enough blow the fuse, the semiconductors that failed will not show up like semiconductor any more, more like a real low Ohm resistor). Please see what are inside the bridge as I have shown earlier.
pin 1 & 2 =
pin 1 & 3 =
pin 2 & 3 =
pin 2 & 4 =
pin 3 & 4 =
pin 1 & 4 =

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

Alright
The mosfets are 11N60C3
On one there is only a reading between pin 2 and 3, which is zero and on diode test reads zero.
On the other, none of the pins register with one another.

The bridge rectifier is a U8KBA80R and by it specific spec sheet pin 1 starts on the left, which is the (-) pin.
so (my dmm is auto ranging and read in the mega-ohm scale):
1&2:1.63
1&3:1.626
1&4:3.15
2&3:OL
2&4:1.637
3&4:1.649

[retiredcaps]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

Alright
The mosfets are 11N60C3
On one there is only a reading between pin 2 and 3, which is zero and on diode test reads zero.

If you measured this out of circuit, then it is shorted (bad).

[budm]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

OK, the MOSFET tested shorted (2 &3), take it out and verify it out off the board, same for the rectifier just to be sure.

[tom66]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

2 & 3 could be a drain source short. If drain gate (probably 2-1) is open the control circuit may not be damaged.

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

pin 2 is a drain. What about the other one?

And all of them were tested out of circuit.

[budm]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

We are looking for shorted out component that has real low resistance to cause the main fuse to blow. If he other show open circuit, then it should be OK. MOSFET should read open circuit on all combination reads of all 3 legs, unless if it has Source/Drain protection Diode, or Gate/Source protection Diode.

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

I guess it would be wise to start checking diodes then?

[tom66]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

When the MOSFET is pulled, do you measure anything on 200 ohm range on meter across the main filter cap?

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

It starts at about 3 mega-ohms and drains. Nothing will show up on that range (well OL) but ya.

[tom66]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

So that's probably the only failed component. What is the part # on it?

[drpj23]

Re: Polaroid FLM-2601 - Power Supply keeps blowing fuse

It is a Rubycon 450v 150uF KXW. There is also T0516.

It is C922 on the board.