Heat Spreading Diode Type Help!!

Discussion in 'The Projects Forum' started by Glowstone, Aug 4, 2015.

  1. Glowstone

    Thread Starter New Member

    Apr 4, 2014
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    Hi All,

    I have been given a Sony Home Cinema system that isnt working. I have ran through a number of trouble shooting/ testing exercises and have found a lot of the main components to be OK ( well the usual suspects anyway)

    What I came across where these 4 heat spreading diodes...all of them are showing the same resistance values in both directions...so I took them out in the hope to replace them.

    [​IMG]

    My issue is, is that I cannot find what rating they are, and also the part numbers I have from the Sony sheets I have are for Sony specified sales only.
    I hear Sony have been known to only use specific components in their stuff? I have even emailed Fairchild to ask them if they know anything about it as these items appear to be Fairchild components. They haven't responded.

    Can anyone help me find these bits, I would be very grateful indeed!

    Reference Sheet

    http://diagramas.diagramasde.com/otros/Sony DVD VCR AVD-K150_DAV-D150.pdf

    Pages 81 and 90 for schematic and parts

    ITEM Board Sony Part Diode

    2x D122 9-885-055-56 F20U20STU
    2x D127/9 8-719-068-69 FMB-G24H

    Kind regards

    Martyn
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    These are similar to an MUR1530. 15 amps will be plenty, these are fast so no issue. Voltage rating will be fine as well. Not a lot of options for diodes specs to worry about.

    Also, make sure there is a little diode triangle molded to the front of the plastic package. If there are two diodes (triangles pointing at or away from each other, then you have more than a single diode. Measure diode voltage from each lead to the heat sink tab on the diode to confirm (metal on back of plastic package).

    http://www.digitroncorp.com/Products/Product-Line/Rectifiers/MUR1530
     
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  3. Glowstone

    Thread Starter New Member

    Apr 4, 2014
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    Many thanks for your quick response!

    I noted these diodes had a single directional arrow on them, thanks for the tip :)

    I am unsure what you meant by measuring voltage on the heat sink tab...the existing diodes dont have metal backing on the heatsink mating surface and are simply plastic backings...do you think that will be a problem?

    Kind regards

    Martyn
     
  4. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    Did you test them using the Diode rather than the resistance setting?
     
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  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @Glowstone.
    If your meter doesn't have a diode function, get a 1k or 100r resistor in series with the diode and measure voltage across the anode/cathode of the diode. Should be zero and about 0.5 to 1.0 volts (depending on the directions).
     
  6. Glowstone

    Thread Starter New Member

    Apr 4, 2014
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    HI, yes I tested them in both, Diode Beep test and resistance method :)

    I am just looking though Maplins Catalog, the similar type I am looking at to the above has 3 leads instead of 2...the ones I pulled off the board looks like the center leads had been removed?

    does that sound normal?
     
  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @Glowstone
    Looks like the mur1530 is no longer in production. Look for a to-220 package on a diode. 10 to 20 amps should be enough.
     
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    No, most of those three-lead diodes are double diodes (anode-anode or cathode-cathode).
     
  9. Glowstone

    Thread Starter New Member

    Apr 4, 2014
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    Many thanks again!

    I may have to pester Farnell or Mouser...

    :)
     
  10. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
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    It might be worth checking those diodes again. Rectifier diodes are usually very robust so for them all to fail in exactly the same way with no outward signs of trauma is, I think, unusual.
     
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  11. Glowstone

    Thread Starter New Member

    Apr 4, 2014
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    @blocco a spirale

    I am pretty confused now as I have just tested them again and they look ok...????

    Diode test function on the F20U20STU type showed readings of 377 and 376 and infinity when reversed

    Test on the FMB-G24H and they show readings of 130 and 131 and infinity when reversed...

    god knows what happened? :(
     
  12. alfacliff

    Well-Known Member

    Dec 13, 2013
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    I just put those part numbers into google, and came up with a bunch of hits.
     
  13. Glowstone

    Thread Starter New Member

    Apr 4, 2014
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    Well after re soldering the Diodes into the board ( was a worthy exercise anyways as they needed new heat paste), I followed the troubleshooting repair guidance and found that a PNP transistor wasnt correct..I took it off to confirm.

    There were readings between the collector and emitter both ways, when I understand that there should have been an infinity reading.

    I managed to locate a replacement and its on order for a measly few pence :)
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Go to the Digikey site and search Littlefuse.
    Gen Purp Diode D4025L etc 15.9a 400v it also has a third lead that is not used.
    Max.
     
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