40 Samsung LN40B500P3F Bad Fuse No AC Power

[XtraTN]

Just bought this LN40B500P3F Samsung for cheap. Opened up the TV and what do you know the main fuse is bad. Looked around the PSU and it doesn't seem like anything was desoldered. First thing I tested was the bridge rectifier, but it was tested good with no shorts. So placed everything back and decided to just throw in a fuse and see what happens.

But I did expect something to blow... Looking around the fuse I don't see anything that would cause the bad fuse except that rectifier, but it was good?

Plugged it in just for a second and what do you know, sparks flew. (Made a video of it) The fuse went bad again. And I found that a piece of that black circular varistor had a piece blown off.. Tested the bridge rectifier again but still no shorts?! I'm so confused what am I missing??

+ ~: measures "1" and 500 ohms the other way.
- ~: measures "1" and 500 ohms the other way.
- +: measures "1" and 1.4k ohms the other way
~ ~: measures "1" both directions

[tom66]

Re: 40 Samsung LN40B500P3F Bad Fuse No AC Power

It can take more than a bridge rectifier to cause a fuse to blow. There are FETs on the board that can short too, test them before you damage more of the power supply with a third fuse.

[XtraTN]

Re: 40 Samsung LN40B500P3F Bad Fuse No AC Power

Youre right, I found two bad FETs. Didn't expect it much cause they were far upstream where the main fuse was.

F1K33AF
FDPF
7N50U

I did see this repair kit before but I didn't see the exact label on my PSU so I wasn't sure if it was the same mosfets... There might also be a bad diode somewhere, but I don't see the exact label on my psu either.

http://www.ebay.com/itm/2x-FQPF9N50-...item3f26ce10f2