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Help!! Control module diode identification

Discussion in 'Troubleshooting and Repair' started by Malach, Aug 23, 2017.

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  1. Malach

    Malach

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    Aug 23, 2017
    I'm working on the control module on a New Holland tractor. Need help identifying a blown diode. I believe it was made by Mitsubishi.Please see pics. It has 4 black dots and thin blue line on it.Any help will be greatly appreciated 15034506746911749867694.jpg
     

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  2. Minder

    Minder

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    664
    Apr 24, 2015
    By the size of the leads it is probably 5a or greater, Look for a 10amp and if on a tractor most likely a low voltage so voltage would not be an issue.
    M.
     
  3. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Have you determined its cause for failure? Such diodes are usually robust and withstand a lot of abuse.
     
  4. duke37

    duke37

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    Have you been welding?
     
  5. Malach

    Malach

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    Aug 23, 2017
    I have done no welding. I've been reseaching on some tractor forums and it seems to be a common issue. This control module costs around $700.00, really wanting to try to fix this one. I'm not well educated on these diodes so if someone could please point me in the right direction it will be appreciated
     
  6. kellys_eye

    kellys_eye

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    Jun 25, 2010
    What makes you suspect it's broken?

    Do you have a complete wiring schematic for the tractor?

    Is there a particular fault that manifests itself as the diode being the cause of it?
     
  7. Malach

    Malach

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    Aug 23, 2017
    The reason I suspect the diode is that both ends look like it burst. This module controls the shuttle shift solenoids for the transmission and I saw on a tractor forum where a member there was having the same problem. He had another module that he could rob a diode from to fix his. Unfortunately I do not have another module.
     
  8. Minder

    Minder

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    Apr 24, 2015
    There is 10amp diodes on Digikey 10A02-TDITR-ND
    One of the reasons for the large gauge wires on a diode is for heat sink purposes, it may be an idea to stand it off a little rather than tight to the board.
    M.
     
  9. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Regardless of the diodes current status (bust) they don't 'bust' without a good reason and given it's a 3A+ diode then 'something' made it go bust that way.

    Unless you find out what it was that caused it to fail then replacing it will just cause the same thing to happen - and if you fit a larger amperage diode you may even propagate the fault to some other part of the system - to greater (worse) effect.
     
  10. Minder

    Minder

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    664
    Apr 24, 2015
    It was mentioned another comparative module with the same problem was solved with the rectifier replacement!;)
    Associated forums indicated a common problem?
    M.
     
  11. davenn

    davenn Moderator

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    Sep 5, 2009
    look closely at the diode, mate ;)

    it's pretty obvious :)
     
  12. Cannonball

    Cannonball

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    May 6, 2017
    With out a schematic and looking at the board, I would take the diode out and measure the traces for a short. If no short replace the diode and watch for smoke .

    It took a lot of current to burn this diode. Good Luck.
     
  13. kellys_eye

    kellys_eye

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    Jun 25, 2010
    I know...... I did. It's not relevant.

    ...but as my next post asks - 'what was the fault that CAUSED the diode to fail?'

    As with fuses, you don't just replace a blown one without finding out what caused it to blow in the first place. And with a suggestion to fit a 'higher rated amperage' diode the possibility for even more damage is high.
     
  14. davenn

    davenn Moderator

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    Sep 5, 2009
    the diode oozing it's guts isn't relevant ???? :rolleyes::eek:
     
  15. 73's de Edd

    73's de Edd

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    Aug 21, 2015
    Sir Malach . . . . .

    How about some more info, to be gleaned from the unit . . .?

    Initially, the heavy blue banded end is being the diodes cathode / negative terminal end.

    It looks as if the diode unit has overheated to the extent that it is expelling its potting agents from each end of its axial leads.

    One might assume that the unit still possibly could be functional, but with its having overheated to have produced these appearances. Or the diode now may just be a shorted junction.

    How about measuring the diode with a DVM in its DIODE test mode and tell us how many millivolts of Vf that diode junction is reading.

    If it’s still having a good junction, that reading will further reveal to us if they happened to have employed a low voltage drop Schottky diode in that position instead of a common silicon diode.

    Some typical values would be up in the 600-700 millivolt range for common diodes or 190-250 millivolts for Schottky or down in the 500-600 millivolt for fast switching silicon diodes .

    I tend to sort of suspect this particular diode function as merely being used in a unidirectional power carrying utilization

    The damnedest thing about your pic . . . if being all BLOWN up for better viewing . . . is that you can clearly see the two round vias that the diode leads are mounted within and a very clear view that there is being a wide foil going upwards from the bottom via and it then passes under the bead of the diode.

    At the top via it also looks as if a like width foil is being routed downwardly ?

    I can’t see the justification, if this uses only 12VDC, but see if there might be a spark gap split, crosscut across that foil in the center. To explain that otherwise direct shorting oddity . . . or just reinspect and be my eyes for me, to confirm...

    The upwardly REFLECTED light from the board precludes any closer examination of the photo . . .fill us in.

    To answer the “ HOT DIODE “ situation. I would initially want to know the Vf reading that you are going to get across that diode and then that will confirm if there is still a good junction and not a dead short.

    Then if the unit still works on the tractor, install the board, but be able to have access to taking readings across that diode. If not possible, use wire leads to remote out connections to be able to do so. Permissible, because nothing other than a static DC voltage is needing to be made.

    Hook up your meter in its DC millivolts range, as this time, your equipment will be supplying the test voltage, in order to estimate the Vf being present across the diode at each stage of testing..

    Then you keep an eye on the meter at the time. . or any involved delay time . . . as you put the tractor into each of the functions that this board is being responsible for.

    At each test transition, IF the millivolts reading rises, that function is pulling MORE current through the diode, find which machine function causes the greatest current demand upon that diode.

    Then you need to track the foil paths from both leads of that diode to see if they might happen to end up at a pull off male/female spade connector.

    If so, then that would provide a VERY convenient point to make an open circuit to insert your DVM in its SEPARATE 10 AMP test lead connection and place in its 10 amp DC range to actually see what current is being passed thru the diode.

    What say ye . . . .

    73’s de Edd
     
  16. kellys_eye

    kellys_eye

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    Jun 25, 2010
    OMG - are you going to pick fault with every typed statement/nuance rather than address the REAL issue? I've got a wife who can do it a LOT better than you can......Have you nothing better to do to up your post count?

    But since you ask, NO, the fact that the diode is oozing its guts ISN'T relevant. It's what MADE IT ooze its guts that's important.

    Changing the diode is child's play. Discovering what made it 'ooze' is the key to resolving the problem.
     
    Last edited: Aug 24, 2017
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