Sharp Aquos TV diode question

Discussion in 'General Electronics Chat' started by Gdrumm, Aug 6, 2014.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    It is a Sharp LCD TV Model# LC-32D62U

    I found a shorted Diode that reads 31DQ04 7H

    I found 2 on Digikey, a 31DQ04-ND, and a 31DQ04TR-NT.

    Which sound right?

    I found a couple of close ones on Ebay as well.

    Should I look deeper, is there likely to be another issue besides the diode?

    It was a curb pick up.

    Thanks,
    Gary
     
    Last edited: Aug 6, 2014
  2. bwilliams60

    Active Member

    Nov 18, 2012
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    I'm not sure what the ND or NT signify on this diode but the 31dq04 Schottky diode seems to have all the same ratings whichever way you choose. What is the symptoms you are having with the TV? What section of the TV did you pull this diode from? Can you post any pictures of the board/TV??
     
  3. RichardO

    Well-Known Member

    May 4, 2013
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    I think you meant "31DQ04TR-ND" not "31DQ04TR-NT". The "ND" on the end means no discount. This is an historical artifact since Digi-Key no longer has any part numbers without ND at the end.

    The "TR" in the number means "Tape and Reel". I don't think you need a whole reel of them. :eek:


    Bottom line:

    What you do want is the 31DQ04-ND but Digi-Key doesnt have any in stock.

    Fortunately, Mouser has the VS-31DQ04 as Part # 844-31DQ04 which appears to be the part you need.
     
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Sounds like me, getting the wrong number.
    It happened with a girl I met one time.

    Thanks for the explanation and part number.

    What about part B of my question.
    There was quite a bit of dust on the components (it was on the power board).
    I brushed it with an old toothbrush, and blew the dust out of the chassis and main board areas.

    Should I desolder and check other components?

    I can take a picture tomorrow afternoon. But the rest of the board looks good.
    As best I can tell, by looking, no parts look cloudy or burnt.

    Thanks,
    Gary

    Symptoms: It would try to turn on, but the blink back off, and a small "OPC" light would come on.
    1. First, solid power light
    2. next Power Light and OPC blink together, twice,
    3. then OPC light blinks by itself three times
    then 2 and 3 repeat themselves until you turn it off, or unplug it.

    The Mouser part shown looks like something from a Star Trek Phaser.
    The one I pulled just looks like a plain old diode, with a dashed grey band on the cathode end. Maybe this is what the factory should have used, but I just want to be sure.

    Never mind, the one shown in the Data Sheet looks correct.
    Maybe this is the new. modern one.
    Thanks again
     
    Last edited: Aug 7, 2014
  5. ian field

    Distinguished Member

    Oct 27, 2012
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    The 04 part of your shottky diodes part number refers to reverse voltage of 40V - SB diodes in general are notoriously low voltage - and manufacturers using inadequately rated SB diodes isn't totally unusual! You could always go for an 06 for that little bit extra safety margin. There are gallium arsenide SB diodes that go up to 90V (last time I looked) - at a price.

    If the diode is the rectifier on the secondary side of the SMPSU, it will have tried to cram AC into its reservoir electrolytic, at the very least check the top for bulging or sucked in by electrolyte depletion.

    Because of their low voltage ratings, Shottky barrier diodes should be handled as if they were static sensitive.
     
  6. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Ian,
    Great information.
    I'll check it thoroughly, and use something to eliminate static.

    Thanks,
    Gary

    And Ricardo, thanks again for the Mouser number.
     
  7. bwilliams60

    Active Member

    Nov 18, 2012
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  8. ian field

    Distinguished Member

    Oct 27, 2012
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    SB diodes aren't quite as fragile as the very early dual-gate MOSFETS that didn't have gate protection diodes - but I wouldn't walk across a deep pile carpet holding it and the poke something earthed with it!
     
  9. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Here are 3 pictures, showing the board and bad Diode.

    I expect to receive the replacement diode the week.

    Thanks for the education.

    Gary
     
  10. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    The Diode didn't fix it.
    The whole board is $31.00 on Ebay, supposedly tested 100% good.

    I tried to download the diagrams, but got this message twice, before I gave up.

    I haven't decided if I want to spend that kind of money for a board).

    Thanks for all your input.
     
    Last edited: Aug 12, 2014
  11. bwilliams60

    Active Member

    Nov 18, 2012
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    Gdrumm,
    Try ShopJimmy.com. Make sure you have all the information off your TV and he will more than likely have what you are looking for. This TV is known for bad caps in the power supply. Are any of them buldged or leaking. Can you take some pics of the caps and post them on here. Should be able to narrow it down for you
     
  12. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    None bulging (see pictures posted earlier).

    I think I fried the diode, actually two of them.
    I ordered 2, just in case, and both are reading a short.
    I guess I don't know what I'm doing with something that fragile.

    So now I'm going to order a wrist band, and try one more time.

    Thanks for the link, I'll try ShopJimmy.com as well.

    Recommended wrist bands?


    I ordered one from Ebay, now the question is how to ground it?
    I Googled, and there are differences of opinion.
    Some say attach it to the middle screw of your wall outlet.
    Some say a water or gas pipe.

    What do you guys do?

    Thanks,

    I checked ShopJimmy, and the only board he had was $72.00 +.

    I saved his link.

    Thanks
     
    Last edited: Aug 12, 2014
  13. RichardO

    Well-Known Member

    May 4, 2013
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    The diodes are not _that_ fragile. I doubt that you damaged both of them in handling. Are you overheating the diode soldering it to a large ground trace?

    If two fried I suspect that there is another fault. The "bad cap" suggestion was good. Without a schematic diagram and more information, other guesses as to the cause are just that -- guesses.
     
  14. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I've got a few days before replacement diodes arrive.
    I will try to find the fault.

    With the diode out of the board, and if there is a short leading up to its thru holes, it makes sense that I could detect that short with my leads in the holes on the board.

    I can disconnect and check the caps, one at a time, there are probably a dozen total.

    Thanks for the feedback.
     
  15. bwilliams60

    Active Member

    Nov 18, 2012
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    Which diode is it that you are shorting. Do you have a location on the board?(ie D21). Which board is it on? What are the meter readings for the diode?
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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    Was that diode *ACTUALLY* shorted? Shottky-barrier diodes do show a bit of leakage as normal.

    With their low breakdown voltage. SB diodes could be the first casualties of uncontrolled voltage rise - maybe check for high or open resistors in the voltage sampling network, then any small electrolytics around the primary side - the small electro's don't usually give the tell tale bulge.

    Re-check the new SB diode, and then check all the others on the secondary side.
     
  17. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    With my meter on the Diode mode, I checked it one way, and got O/L (as expected).
    When I checked it the other way, it sounded an alarm (like a coductivity meter test).

    When I checked other diodes in my stash, they didn't sound any alarm.

    Would a Schottky sound an alarm like that?

    Thanks for the other clues as well.

    It gives me a place to start.

    One of my earlier posts showed the board (power I think), and the void and symbol where I had removed the Diode, and the number written on the board (D5705).

    HTH,
    Thanks
     
    Last edited: Aug 15, 2014
  18. ian field

    Distinguished Member

    Oct 27, 2012
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    ON the diode check mode your DMM should display the forward volt drop.

    You can expect down to 0.2V for a power SB rectifier The small signal variety read a little higher.
     
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