MOSFET Transistors from LCD TV

Discussion in 'General Electronics Chat' started by Seki, Oct 28, 2013.

  1. Seki

    Thread Starter New Member

    Oct 28, 2013
    6
    0
    Hi all,

    I have recently acquired a faulty LCD TV that does not power on. I popped oven the back cover and tested the fuse on the switching power supply board which was blown. I then replaced the fuse however it went straight away as soon as the power was switched on from the wall. At this point I knew there must be a short someone in the PCB causing the fuse to blow.

    I then tested the diodes and bridge rectifier which all turned out to be fine. Eventually I located 2 MOSFET transistors when was reading short no matter how I tested it. My multimeter kept giving me 0 on the continuity test on every leg regardless of polarity.

    These 2 MOSFETS has the following text engraved on it...

    NIKOS
    P1260ATF
    SUE2N1A01

    and a picture...
    [​IMG]

    Uploaded with ImageShack.us


    I was able to locate the data sheet for the failed MOSFET transistors http://www3.use.com.tw/webdata/niko/P1260ATF(S)_REV 1.0_20100809.pdf but I don't particularly understand everything. I have some experience with electronics such as replacing capacitors but this is the first time I'm dealing with these types of transistors.

    I tried to source an exact replacement online but I'm not having much luck, apart from a few sellers from China who has a minimum order of 10! Is there an alternative transistor that I can use or something?

    Much appreciated!
     
    Last edited: Oct 28, 2013
  2. wayneh

    Expert

    Sep 9, 2010
    12,085
    3,024
    Once you know whether it's N or P-type (N in your case), look at the specs for voltage and continuous current. I'd be nervous replacing these with any lower numbers on those two key specs. In your case it looks like 600V and 12A. You can see that the data sheet highlights these two specs (plus the on resistance) in the product summary. Could I live with 500V and 10A? Maybe, but it would bother me.

    Also pay attention to package size. It makes life easier if the package is the same, especially if there if a heat sink is involved.

    Finally, be prepared for other things being wrong, beyond the two MOSFETs. You win some and lose some.
     
  3. Seki

    Thread Starter New Member

    Oct 28, 2013
    6
    0
    Thanks for that wayneh. I've been trying to find a replacement of similar specs but have failed miserably, the maximum voltage on the ones I found was 500v. It seems like these failed MOSFETs are top of the range?

    I'm thinking of buying the pack of 10 from alibaba, but although those have the same product code, P1260ATF, the text on the third line is different. Is there a significance regarding the text on the third line or could it be just a batch number?

    I understand that there could be other problems that caused the MOSFETs to fail or that the shorted MOSFETs may have blown some other components. I noticed that the drain on the first MOSFET feeds directly into the source of the second, is there a possibility that the first MOSFET took out the second one in this arrangement?
     
    Last edited: Oct 29, 2013
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,733
    759
    U should check the gate drive resistor and or diode placed between the PWM and MOSFET gate.

    If the driver out is shorted u will blow the new ones. If the Drain and gate pins are shorted, the gate driver will see RAW DC and most of the time will blow up too.
     
  5. Seki

    Thread Starter New Member

    Oct 28, 2013
    6
    0
    I have tested the components in the yellow boxes with my multimeter and they seem to check out fine. Resistor 22RD was reading 22 ohms exactly and resistor 10RD was reading 10 ohms exactly. I had to remove the diode from the board to test it because the resistor connects to it in both directions but it seems to check out fine too, it was reading 950 on one side and OL on the other. I'm not keen on removing the the diode from the second MOSFET as these row of components are eproxied onto the PCB and I don't want to damage anything.

    Do you see anything else that might be worth testing?

    [​IMG]
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,085
    3,024
    I took a look at Mouser and there seem to be lots of options.

    Maybe this one, for instance.
     
  7. Seki

    Thread Starter New Member

    Oct 28, 2013
    6
    0
    Thanks. I note that the one you have chosen has a lower gate-source breakdown voltage and a lower resistance. Will it be ok?
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,733
    759
    If the gate resistors checks out then most of the time the driver will be fine

    {ed}
    I see the gate is driven by a small transformer. Then all else will be fine
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,085
    3,024
    "Chosen" isn't really the right word. I spent a few seconds finding one that was cheap and met the two specs in the right package. There are many other choices.

    But to answer the question, I believe the lower threshold and resistance are not problems. They are both in the category of "less is better" for most applications. I'm no expert though, so it'd be nice to hear from someone who is, if Rds or the threshold voltage can ever be "too low".
     
  10. Seki

    Thread Starter New Member

    Oct 28, 2013
    6
    0
    As I didn't have time to go through the entire selection of transistors, I went to one of the Chinese sellers and ordered the original NIKOS P1260ATF transistors. They should come in 2 weeks time.

    I'll keep you guys posted on the repair, whether I could successfully bring the TV back to life. It's a 50 inch Panasonic which I bought for just £142 on eBay!
     
  11. TorontoBob

    New Member

    Oct 5, 2013
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  12. Seki

    Thread Starter New Member

    Oct 28, 2013
    6
    0
    OK, it looks like I'm in some trouble...

    The MOSFETS has finally arrived from China yesterday after an agonizing wait so this morning I wasted no time and got to work. I replaced the two original MOSFETS which had originally failed, applied thermal grease and checked the board by plugging it into the wall. The board at this point has not been installed back onto the TV, I was just testing for voltages and signs of anything untoward but there was none. The filter capacitor charged up and it all seemed fine and dandy.

    I removed the main power cord from the wall, discharged the filter cap, installed it back into the TV and plugged all the cables back in. About two seconds after I switched it on from the wall, the fuse blew with a blue spark from the fuse holder! Oh dear I thought!!!

    I pulled the brand new MOSFETS from the PCB and tested it, it was shorted like the originals. I know something is seriously wrong which blew the MOSFETS which in turn blew the fuse. I have a feeling that failed capacitors might be a culprit, but I don't have an ESR meter to test.

    Could faulty capacitors blow these MOSFETS or other reasons? Much appreciated for any help with the diagnosis.

    I have attached a picture of the circuit board showing the components side

    [​IMG]
     
  13. wayneh

    Expert

    Sep 9, 2010
    12,085
    3,024
    Hate to say it, but I told you so.

    You can detect a bad capacitor without an ESR meter if it has failed to open or short. If it's still got the proper capacity, it could indeed be an ESR problem, but the odds are going down that the cap is the problem.


    Do you have a schematic or a service manual? Pretty tough without that.
     
  14. tindel

    Active Member

    Sep 16, 2012
    567
    193
    Sounds like the power supply is working just fine... It's just when you plug it into the rest of the TV that you have the problem right?

    If that's the case then you probably have a short somewhere besides the power supply... Probably on another card.. You can try to track this down by looking for a short on the connectors of the other cards.
     
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