Samsung 912T click then off

[sceva]

The ccfl's come on for an instant and then go off. I can hear a click (when the the lights flash) somewhere on the inverter side of the board, but can't tell where.

I found a bulging cap at C617 between the two inverter transformers and replaced it. 470u/25v But no change in symptoms.

Also tried external ccfl's and no change.

The on signal from the main board stays on after the lights flash.

I have never seen the raised circuit board before. Should I remove it and take a look? I am hoping someone has an idea of what the click is!

Thanks.

[retiredcaps]

Re: Samsung 912T click then off

I have never seen the raised circuit board before.

Pics?

[sceva]

Re: Samsung 912T click then off

I hate this because these are the clearest, sharpest pictures yet! I did add them before, but the website upgrade must have zapped them!

[retiredcaps]

Re: Samsung 912T click then off

I have never seen the raised circuit board before. Should I remove it and take a look?

Check out this "samsung 920N, MJ19BS inverter/power board fault"

https://www.badcaps.net/forum/showthread.php?t=8453

[sceva]

Re: Samsung 912T click then off

That is my board, except mine is Rev MP 3 instead of 5. I will take it off and have a look. Thank you.

[Dgtech]

Re: Samsung 912T click then off

From looking at the pins on the hybrid board, there is some discoloration from heat. Dont forget to check FH601 and FH602 (2 round red fuses)

[sceva]

Re: Samsung 912T click then off

I have the small board off, and the component in the bottom right is definitely damaged. It is burnt, and the other board underneath it shows burn also. It looks like the numbers on it read:
The first letter which might be the manufacturer's symbol is a forward slanting "F".
PE7A0 (I am fairly confident this is correct)
FDS (there could be more letters but I don't think so)
4935 (this could also be 14935 but can't tell for sure)

Any ideas where to get a replacement part for this?

The link here: https://www.badcaps.net/forum/showthread.php?t=8453 looks like my board but the part number he shows is different.

Thanks.

[Dgtech]

Re: Samsung 912T click then off

Here is the data sheet. The discription of that part is Dual 30V P-Channel PowerTrench MOSFET. There is a guy selling it on ebay for $11.

[retiredcaps]

Re: Samsung 912T click then off

Here is the data sheet. The discription of that part is Dual 30V P-Channel PowerTrench MOSFET. There is a guy selling it on ebay for $11.

$1.25 at Digikey

http://search.digikey.com/scripts/Dk...=FDS4935ACT-ND

You might want to test the MOSFET (both of them) to see if they are shorted or not.

[sceva]

Re: Samsung 912T click then off

Digikey and mouser don't have any in stock. The one on ebay has a different set of letters across the top: P42DN - mine says PE7A0, but the rest of the numbers are the same. Will it work? (it is 10.99 for 5 pieces).

[Dgtech]

Re: Samsung 912T click then off

The other numbers are often a lot number or date code. The important numbers match. I found another one at this site:

http://www.alliedelec.com/search/sea...ry&Ntt=fds4935

Go with the FDS4935A on that page.

[retiredcaps]

Re: Samsung 912T click then off

TI found another one at this site:

http://www.alliedelec.com/search/sea...ry&Ntt=fds4935

Go with the FDS4935A on that page.

If the Allied doesn't work, some sellers on ebay, when contacted, will sell you modified/customized versions of their listings.

For example, I only needed 1 IC and the guy was selling 5. So I wrote him and offered him a price for 1 and he accepted by making a customized listing for me.

[sceva]

Re: Samsung 912T click then off

Thanks so much for the help locating some parts. I don't know enough about the parts to know, for example, if I look up fds 4935 on digikey, there are about 4 parts and I can't tell which is the correct one...

I called digikey about the one mentioned above, and they said they did not know if/when they would have any in, but suggested http://search.digikey.com/scripts/Dk...=785-1058-1-ND as a replacement. Could someone check and see if this might work? The original part at digikey is http://search.digikey.com/scripts/Dk...=FDS4935ACT-ND.

I also contacted the eBay seller to see if he would sell a smaller quantity.

Thanks so much.

[Dgtech]

Re: Samsung 912T click then off

I reviewed the data sheets and this will be a perfect match. The specifications and pinout match up. Do make sure that you observe the orientation of the part when you remove it.

[sceva]

Re: Samsung 912T click then off

I reviewed the data sheets and this will be a perfect match. The specifications and pinout match up. Do make sure that you observe the orientation of the part when you remove it.

Awesome! I have it on order and will update when it arrives.

[sceva]

Re: Samsung 912T click then off

I replaced the FDS4935 and still get the same result - backlights flash on/off, and a click occurs at the same time... aaarrrgg.

[retiredcaps]

Re: Samsung 912T click then off

I replaced the FDS4935 and still get the same result - backlights flash on/off, and a click occurs at the same time... aaarrrgg.

Did you test the other non burnt out mosfet to see if it is shorted? Maybe try testing ZD1 and ZD2 next to the burnt mosfet that you replaced to make sure they are working?

[retiredcaps]

Re: Samsung 912T click then off

I replaced the FDS4935 and still get the same result - backlights flash on/off, and a click occurs at the same time... aaarrrgg.

Have you tested T602 and T603 for open windings using an ohms test or shorted turns using a ring tester?

[jetadm123]

Re: Samsung 912T click then off

Hello! Even with substitution of the fds4935a, there's always the chance that there still could some incompatibilty between the old and new chip. Ideally, you should have replaced both the burned out chip and the one above it. I've included a pdf file of the inverter controller, OZ960. If you look at the application circuit you can test to make sure it's getting the proper voltage at pin 6. Also note that the U1 and U2 config is a little different than yours, since each chip has a N and P-channel mosfet in it.

[sceva]

Re: Samsung 912T click then off

The mosfet near the one I replaced seemed ok when i tested it, but I didn't remove it from the board... I will test it again when I get the board back off (seems like a foolish way to mount a board onto another board!) and test ZD1 & 2 also.

I have tested T602 & 3 and they showed ok with the ring tester.

The chip above the one I replaced has a different part number than the one I replaced. When I first looked at the board I thought they would have been the same, but after looking thru the magnifying glass I saw they were different. It is possible one or the other were replaced before?

I have no idea how to test the small board for proper voltage, since I have to desolder it from the main board to see the components. I guess if I had a power supply I could power it up that way, but without being connected to the inverter transformers I think it would shut down anyway?

No one has commented on the clicking noise. Any idea which component would click?