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T3J81 (Zener Diode ?)

Discussion in 'Datasheets, Manuals and Component Identification' started by ldcarter, Nov 20, 2016.

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  1. ldcarter

    ldcarter

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    Nov 20, 2016
    Hi to all. New to this forum and am trying to repair a Portable Generator power supply. The part is question is labeled T3J81 (the T3 on one line and J81 just below). The housing type is SOD-64 I believe. It has a band on one end leading me to believe it is a diode, the image I found of it said it was a Zener diode. Found nothing on Google when I entered the full number but using just "T3 diode" showed it might be a "avalanche diode". I think it may be a 81V Zener diode, or possibly 8.1V. Anyone seen one of these and can tell me what it really is and perhaps a substitute. There are 3 of these, you can see them in the image just below the loop in the white wire, to the right of the pair of diodes, and left of the resistor. DSC02522.JPG DSC02522.JPG
     
  2. dorke

    dorke

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    Welcome to EP.
    It is indeed a diode,but hard to say which.
    The package could be other SODs like 57,61,83 can you please measure it (both dimensions).
    If you can ,try to make a small diagram of what the diodes are connected to.
    Is this grainy material sand?
     
    Last edited: Nov 23, 2016
    HellasTechn likes this.
  3. Colin Mitchell

    Colin Mitchell

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    They are 2 amp diodes, maybe up to 1,000v They are not faulty.
     
  4. ldcarter

    ldcarter

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    Nov 20, 2016
    Thanks for the replies. Now to answer some questions. The part is 3.78mm in diameter, 5.45mm in length, the leads are 1.28 diameter. The grainy material is many years of dirt, sand, etc. on top of a potting material (which I am carefully trying to remove). I took one of these diodes out and measured 500 ohms forward biased and infinite reversed biased. I then took three 9v batteries and connected them using a 2.2k resistor to obtain 30 volts (new batteries), hooked them to my meter using one set of leads, and connected another set of leads from the same source and reversed biased the diode and got 30 volts. If I did everything right then this is a zener diode of more than 30 volts, so perhaps the j81 means 81 volts. I do not have a dc power supply to test it at this 81 volts. The circuit board is labeled Generac 59459 from a Dayton 7500 generator. No luck finding out anything on those either, but perhaps I'm not asking the right questions. I contacted Generac but they were no help, but the generator is probably older than anyone I spoke with. The source of the zener diode tester is on Youtube. Attached is a picture of the rear of the circuit board with the connections. Exc. stands for the excitation windings on the generator, Rotor Neg. is the negative brush going to the rotor. Rear Labeled View 3.jpg
     
  5. duke37

    duke37

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    If the diode is faulty, it would likely show the same connection in each direction, either open circuit or short.

    Some information on the generator may help. Three diodes side by side may be rectifying three phase from the alternator.
    I woukd guess that Colin #3 is correct.
     
  6. davenn

    davenn Moderator

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    or it more likely means they are just plain diodes, not zeners
     
    Last edited: Nov 23, 2016
  7. ldcarter

    ldcarter

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    Nov 20, 2016
    Thanks again for the responses, this is an Industrial Generator used for job sites. 18HP 2 cylinder engine running a 7500 watt generator but it is only single phase. Davenn thanks for the suggestion about it being only a diode, I used the same checker to test a regular diode and reverse biased the voltage read 30 volts. Now I at least know that the diode you're testing must be a Zener for this to work.

    When i found an image of this particular diode, I went to the address that posted it and they showed it be a Zener. It seems that the only way to check if this diode is really a Zener is to find someone with a dc power supply and see if it does cut off at 81v.

    Colin Mitchell mentioned earlier in this discussion that it could perhaps be a 2 watt 1000 volt diode. If I find that this is not a Zener, and no clue as to its actual value should I (if need be) attempt to find a diode that physically matches this one? Would an "oversize" in terms of voltage matter to the circuit?
     
  8. davenn

    davenn Moderator

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    hmmm OK .... I was going by your other testing info

    what address ?? share the link please
     
  9. Colin Mitchell

    Colin Mitchell

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    1. All diodes are zener diodes. Some have a higher breakdown voltage.
    2. All zeners need a breakdown-resistor in series.
    3. Test the diode with a 300v zener tester as shown on talking electronics website and overcome the worry it is a zener.
     
  10. ldcarter

    ldcarter

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    Nov 20, 2016
    My thinking is "if" it breaks down and shows 81v on the meter with an input of more than 81v, then it is a Zener diode. This is the Youtube video website. . As to the link, I had to copy and paste just now to get it to work. I thought if I pasted it here, you could just click on to get it to work. I have done that in the past and they usually show up that way, did I do it incorrectly? Wasn't sure if you were allowed to link so thought better safe than sorry. Couldn't make this device for less than a dollar though, cost me almost $7.00 for the batteries and the resistor. I have some friends that are Ham operators, they may know someone with a dc power supply.
     
  11. ldcarter

    ldcarter

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    Nov 20, 2016
    Just hit "Post Reply" and see that the website popped up. How neat is that. The more time I spend time here the better I like it. Members willing to help and great features. See that I don't need the copy and paste comments I entered previously.
     
  12. dorke

    dorke

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    Jun 20, 2015
    The 2 SCRs are 6A/600V,(Teccor -now days Littlefuse, case should be T0-220 or TO-202).
    They look to be connected to the diodes like shown below.

    The unknown diode looks to serve the purpose of protection .

    Why do you think they are defective?
    Is any of them shorted or open in both directions?

    What is the 3rd diode(closer to the center of the board) connected to?

    D-scr.JPG
     
  13. ldcarter

    ldcarter

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    Nov 20, 2016
    Dorke, attached is the image with all the components labeled. Haven't removed the potting around the diode you asked about so I can't yet give you the actual number, but it is labeled with the + location as a diode. I do not suspect the "T3J81" diodes as defective, but something is causing the generator to not put out any power. Checked the windings on the rotor and stator and flashed the generator but still no output. Suspect the voltage regulator but maybe not. I know that you cannot check any component with any certainty when it is still in the board so am in the process of removing the components and checking them all. Plan to replace those I cannot check as this board and some of its components are made of unobtainium. Thought if I could get a replacement number for this component I would just replace them.
     

    Attached Files:

  14. duke37

    duke37

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    The way I have tested 'surplus' diodes is to use a high voltage supply and measure the voltage of this with a meter. Interpose the diode to see the amount of voltage drop. I used a meter with an input resistance of 1M which limits the current, I went up to 1000V for high voltage diodes - you need to be careful.
    A Megger could also be used.

    You could get a medium voltage by rectifying the mains to charge a capacitor. I presume that you have 110V which will give you 155V. Use an isolation transformer and earth trip for safety, only switch on when you have stood back.

    Have you tried the alternator with an external energising voltage? Does it have brushes or is is brushless with a rotating rectifier?
    I have used a battery charger and a Variac to give a low voltage supply.
     
  15. dorke

    dorke

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    Jun 20, 2015
    Lets start from the beginning.

    You have a generator that spins but doesn't put out voltage.
    You want to fix it and,suspect the AVR board is at fault.

    Have you verified that the brushes are good ?
    Have you checked the windings?

    BTW,if the diodes are fine leave them be they are not the cause of the problem.
    This AVR looks like it uses 2 SCRs triggered by a UJT transistor.
    Most likely a 741 op amp is used has a comparator to fire the UJT.
     
  16. ldcarter

    ldcarter

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    Nov 20, 2016
    Duke37, Is that an old Field Marshal Tractor? I have attached a 12v battery to the brushes (per instructions), and used a 9v battery to the receptacles per the Generac web site. Are you suggesting using the 110v house supply connected to the generator with lights method. I have worked with 550 3 phase, and many other voltages, but I must admit the thought of connecting 110v directly to a portable generator scares me. 30 years ago I had lots of test equipment and access to many others but now I have only my old Simpson 260 and a few digital meters.

    Dorke, I pulled the brushes, looked great, tested good with my ohmmeter, did the same to the windings. I must admit though I can only test them through generic readings as there is no data on this unit that I can find anywhere. It was sold by Dayton (out of the generator business, and no archives), and manufactured by Generac (again no archives at Generac, but they are more than willing to sell you a new one as this one is not worth repairing). Also, the diodes you asked about, the one that goes left to right on the image is a BZY97C130, the one that goes up and down starts with BZY and can't see the rest yet but I suspect it is the same type. A web search of those showed them as Zener diodes and of course too high a voltage to see if my $7.00 Zener diode tester actually works.

    As to the diodes that started this thread, removed the potting around the first one, then removed the diode using a soldering iron and solder sucker. Began to remove the potting around the second and the diode pulled apart where the anode connects to the wire. My fault, probably, but I was using a razor to cut the potting away and not prying on it. Also found the wire that connects to the excitation had maybe one strand and the potting holding it to the board.

    These are merely bumps in the road though, if this generator is fixable I will fix it. Then of course sell it for a loss or give it away and get some other project.
     
  17. duke37

    duke37

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    The tractor shown is a Nuffield Universal petrol/TVO.(Morris Motors). It was produced in the 1950s with 5 speeds and electric starter and was a vast improvement on the 3 speed Standard Fordson. It was developed over the years and was taken over by Marshal, then abandoned.
    The Field Marshal was a single cylinder two stroke diesel with a Casey Jones smoke stack to collect the filthy black oil. I have seen one started by hand - quite a performance. If you were rich, you used an explosive charge.

    Give the resistance of the rotor and the quality of the brushes and slip rings. Then a guess can be made of the voltage to be applied, I suggested a battery charger but you appear have some instructions to say try a 12V battery. If you get output, then the fault is in the control board.
    The board can be fired up with a Variac from the mains and the output measured as input voltage is changed, it should rise as the input rises until 110V is reached when it should reduce. Use a 100W lamp as load.

    I recently looked at an italian single phase/three phase tractor driven brushless generator. The controller was faulty and covered in epoxy so not repairable. A new board could be obtained from the US for about $400 but I got one from china wihich looked like the original for about £70
     
  18. Bluejets

    Bluejets

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    Do you have a model number for this Generac machine??
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No they're not. You're probably thinking about avalanche breakdown.
     
  20. ldcarter

    ldcarter

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    Nov 20, 2016
    Duke 37 so the company that made Morris Minors and Travelers made this tractor. Saw them restore a Morris Traveler on "Wheeler Dealers". Had to look up a Variac to see what it was. Don't have access to one of those, had never even heard of one. Is this in line with the 110v direct hookup you mentioned? Anyway this is a Dayton 4W113 7500 Watt portable generator (Briggs & Stratton 18HP 2 cylinder engine with a generator made by Winco). The part number on the board (this board is part of the control panel where the on/off and receptacles are located) is Generac 59459 which can be cross referenced to a B&S 83048GS if the numerous twists and turns I followed trying to find out some information on this board are to believed. Of course there are no pictures on any of the web sites I visited so that perhaps I could see if their board was indeed what I had with only one site that even stated they had one. That site claimed they had one for over $300 dollars (240 pounds, is that right the pound is worth less than one dollar?) but no picture with a no return policy. As to the epoxy, you can carefully use a heat gun and the epoxy will turn brittle and makes it somewhat easier to remove.
     
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