Samsung Syncmaster 713N no power

[zsirfoka]

Hi!

The problem:

My son's LCD ceased to work a week ago, he was watching some cartoons on it when suddenly it powered off, power led went off. I did not see smoke, but I could smell it in the air.

What I've done so far:

After I disassembled it, i saw burn marks under the IC marked U320.

Also thought, while I'm at it, i'll change all the capxons to some higher quality ones. Desoldered them all, and just for curiosity I measured capacitance in all of them. C661 or C662 was half the rated capacity, and couldn't get a reading on the big cap, so I guess that was bad too. Tried to find rubycon/panasonic/other high quality caps, but for some values I only found samwha and hitano in my local shop. Anyway, I changed them all to new ones.

Changed the burned IC (it was a TOP246FN), also F110 fuse was blown, so changed that too to an identical one.

Still not powering on, I can't get 13V or 5V reading on the output side, I have ~330V on the big cap tho.

Any ideas what to test next?
I'm thinking bad diodes, in that case which one should I start with?

Thanks in advance.

[Per Hansson]

Re: Samsung Syncmaster 713N no power

Zener diode ZD111 looks burnt, or is it just from the IC exploding?
Anyway I'd look at that and also they nearby diodes D321 D320.
If they are ok then continue checking diodes further out.

[zsirfoka]

Re: Samsung Syncmaster 713N no power

As I saw, the burn mark was from the IC indeed.
I'll look at the zener as I get home from work. Markings on the zener diode: 4744A. A quick google search identified it as a 15V 1W zener.

I looked it up in my local electronics shop, but they don't have this exact type.
They have this :BZX85C15, the shop sells it as 1.3W, but on the data sheet it is 1W.
I'm a bit confused, can I use this for a replacement?

[Per Hansson]

Re: Samsung Syncmaster 713N no power

Sure that would work fine, should be an exact replacement.

[zsirfoka]

Re: Samsung Syncmaster 713N no power

ZD111 and D321 were shorted. Replaced them. Now there is a high pitched whining noise like every second, when i plug it into the mains. I can measure approx 15v on the 13v output and 5v on the 5v.

Hooked up to the main board and the power switch, the power led lights up with the start of the noise, then fades for a second, lights up... fades... and so on...

[Per Hansson]

Re: Samsung Syncmaster 713N no power

So more things are toast, just keep hunting for diodes at this stage

[boyebaran]

Re: Samsung Syncmaster 713N no power

hi
please replace c320&c323 and big electrolytic cap (68 or47 ,...400 volt)

[zsirfoka]

Re: Samsung Syncmaster 713N no power

Thanks for the suggestion, I've already replaced those caps, in fact, I've replaced all the electrolytic capacitors on the board.

Checked all of the diodes around the ic, even the smd diode on the backside of the board, they were ok.

To one of my colleagues advice, I've changed the optocoupler (PC330), and that seemed to be the last fried component, as the lcd is up and running now.

Thank you all for the guidance.