resistor burned

Discussion in 'General Electronics Chat' started by moss99, Feb 15, 2009.

  1. moss99

    Thread Starter Member

    Feb 15, 2009
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    Hi all i am just starting to try and learn a bit about electronics and have audio reciever of my nephews which got rain on it it switches on for about 5 seconds then gos back to standby ,
    i have found a resistor which is burned quite badly and have de soldered it from the board and have a resistance of 51k ohms but it has burned all the colours off R225R is stamped on the board beside it does this have any meaning as to what the resistor value is ?

    thanks
    mark
     
  2. flat5

    Active Member

    Nov 13, 2008
    403
    17
    It has meaning if you have the service manual or schematic diagram for the TV. It is a part reference number for the schematic. Not the same as the resistor value or the manufacturer's stock number.
    Give us the model number for the TV and perhaps the chassis number and someone here may be able to help you.
     
  3. moss99

    Thread Starter Member

    Feb 15, 2009
    12
    0
    Hi thanks for the reply it is a sherwood av amp RD-6106R
    if the resistor is badly burned would this be the likely cause of the fault ?
     
  4. john-campbell

    Member

    Feb 10, 2009
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    It's more likely that the burned resistor is a result of a fault somewhere else. Since it was rained on the water probably shorted something out and caused one or more components, including the resistor, to burn or fail. If the water has since evaporated the original fault may no longer be present. Since resistors are cheap you can simply replace it, once you determine its original resistance value and wattage. If that doesn't fix it or if the new resistor immediately gets too hot you will need to obtain a schematic and troubleshoot it in the normal manner.
     
  5. moss99

    Thread Starter Member

    Feb 15, 2009
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    Hi yes the water shorting was what i was hoping just got to try andfind out what the resistor was now :confused::confused:
     
  6. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Audio receiver...I would guess that the water got on one of the output transistors and shorted (sort of) the collector to the chassis (ground). Is the resistor near one of the big metal transistors?
     
  7. moss99

    Thread Starter Member

    Feb 15, 2009
    12
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    Hi the burned resistor is around the other side of this i think voltage regulator.. see photo .. (please correct me if im wrong ) which i have just noticed has a chunk missing out of it im assuming these get hot (Large heatsink) possibly water got on this P1000666.jpg
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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  9. moss99

    Thread Starter Member

    Feb 15, 2009
    12
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    this is wher the resistor was to pcb.jpg
     
  10. flat5

    Active Member

    Nov 13, 2008
    403
    17
    Looks like the transistor on the left (Q2 ?) shorted out and took the emitter resistor with it to wherever dead parts go to.
    Google on how to use a multimeter to check transistors.
    The pair on the left probably will need to be replaced.
    Look to the other channel to see what the resistor used to be.
    The L & R amps will be the same. Understand?

    Edit: I don't think it is a regulator. I think these big transistors all in a row are the power output transistors for the Left and Right channels.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    Comparing the photograph you posted with the "equivalent circuit diagram" of the NPN transistor on page 1 of the datasheet, it appears that the fried resistor is connected to pin D of the transistor.

    Looking on page 2 of the datasheet, that resistor basically would be a "select on test" value, somewhere between 200 Ohms and 0 Ohms. After replacing the transistors, you would use a potentiometer wired as a rheostat, and carefully adjust the pot until there was 2.5mA current flowing through it.

    Although transistors are produced by the millions, each is unique and has slightly different characteristics. The value that was appropriate for the original transistors probably will not be appropriate for the replacements - if you can find them.

    The big problem of the moment is that I can't find anyone who stocks those transistors!
     
  12. SgtWookie

    Expert

    Jul 17, 2007
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    Went on the Sanken website and found this cross reference:
    http://www.sanken-ele.co.jp/en/prod/semicon/pdf/discon_e.pdf
    The SAP01N has been replaced by the STD01N
    The SAP01P has been replaced by the STD01P
    The STD01x are not identical to the SAP01x
    STD01N,P datasheet:
    http://www.sanken-ele.co.jp/en/prod/semicon/pdf/data_std01n_pe.pdf
    This means you would have to do some creative wiring.

    USA distributors for Sanken products are:
    Allegro MicroSystems, Inc.
    115 Northeast Cutoff, Worcester, Massachusetts 01606, U.S.A.
    Tel: 1-508-853-5000
    Fax: 1-508-853-3353
    Allegro MicroSystems, Inc.(Southern California)
    14 Hughes Street, Suite B105, Irvine, CA 92618, U.S.A.
    Tel: 1-949-460-2003
    Fax: 1-949-460-7837

    They didn't appear to have any in stock themselves; when I performed a search for the part numbers, it provides a link to another distributor who has a $50 minimum order. Although the search result indicates that distributor has 20 in stock of each, it also says the minimum order quantity for either is 400, and lead time is 8 weeks.

    I'd start by calling Allegro Microsystems.
     
  13. moss99

    Thread Starter Member

    Feb 15, 2009
    12
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    Hi i have found out the resistor value via e-mail from sherwood (22 ohm) looks like i might have a bit more of a problem with the transistor though..

    I think this might be a bit much for a first project ;;;;;;



    Looking on page 2 of the datasheet, that resistor basically would be a "select on test" value, somewhere between 200 Ohms and 0 Ohms. After replacing the transistors, you would use a potentiometer wired as a rheostat, and carefully adjust the pot until there was 2.5mA current flowing through it.

    ((i dont really understand this ,,,i am trying to learn though ..
     
  14. moss99

    Thread Starter Member

    Feb 15, 2009
    12
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    Hi again thanks for all your help by the way , I am trying to find a schematic download for anything for free ,, just to have a look at what is the best way to word it in google ?

    P.S do i have to de solder the transistors from the board to test accuratly
    also of the 5 wire there is base collecter emmitter what are the other 2

    Thanks again

    mark.
     
  15. moss99

    Thread Starter Member

    Feb 15, 2009
    12
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    Hi i have removed the transistors and you are right 2 are gone .
    the resistor was on a board which was not symmetrical to the other side but i have the resistor value now from sherwood (22 ohm) ,(thanks flat 5)

    Sgt wookie , I have spoken to B&D enterprises and it will cost me $80 to get the transistors to me (uk) for an amp that is worth about $60 ,and still might not work with new parts ,
    i am awaiting a reply from allegro micro systems ,,
    Surely someone somewhere must have these transistors on a shelf or in a broken amp its just a matter of finding them .....

    mark
     
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