Looking for transistor

Discussion in 'General Electronics Chat' started by kbxc20, May 31, 2015.

  1. kbxc20

    Thread Starter New Member

    May 27, 2015
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    Hi,
    I have a Transistor that is partially burned and can read only a portion of the number. 2sk is all and not 100% sure on the k, so not much info. I think the size is a TO-247. See the picture. The board is a voltage regulator and negative 12 to 18 volts approximately would go to the right pin (burned away), then out the center pin to an exciter circuit. There is a fuse of 6 amps on the positive side of circuit that should have prevented this.
    I assume the left pin is the base. Also the transistor on left checks ok, [​IMG] and part on right is a D5LC40 rectifier. I think its bad as it checks 0 resistance both ways from center pin to left pin. Board powers up and may be ok except for above. Would like to try something that may work similar to the original component.
    Thanks in advance
     
  2. ian field

    Distinguished Member

    Oct 27, 2012
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    2SK is almost certainly a power MOSFET in that case style. The number could include 2SA, 2SB, 2SC or 2SD - all of which are bipolar transistors.

    IIRC: the TO247 is very similar to the TO3P or perhaps a bit bigger, purely a guess; that's probably rated AT LEAST 10A, if its a flyback converter the voltage rating may need to be even more than 8x the DC feed voltage.
     
  3. kbxc20

    Thread Starter New Member

    May 27, 2015
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    Thanks, if I could find a component that "might" work I would give it a try. The output goes to a exciter coil in an ac generator, but i'm no electronics expert for sure.
     
  4. ian field

    Distinguished Member

    Oct 27, 2012
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    A good way to learn is read up on component symbols and get an idea what the actual parts look like, you may start to be able to identify the parts around the burned device, if you can follow the PCB tracks and sketch out how they're connected together - you're half way to a schematic.

    Or you could just google for the schematic and post it here.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I can not see any picture in your openings post.
    Please upload the picture to the forum using the "Upload a File" button below the reply box.

    Bertus
     
  6. kbxc20

    Thread Starter New Member

    May 27, 2015
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    Here's the picture
     
  7. ian field

    Distinguished Member

    Oct 27, 2012
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    All that really tells us is; the MOSFET source lead has been consumed by an arc - probably started off by a dodgy solder joint.

    We can surmise that there's a fair bit of inductance involved for the arc to do that much damage.

    Get a basic electronics book and study how to identify the components - the track pattern looks pretty simple, so you can execise your new found knowlege by tracing out the circuit.

    There's probably other damaged components caused by that burn up, so once you can identify each component it would be a good idea to take out the likely suspects one by one and test them.
     
  8. kbxc20

    Thread Starter New Member

    May 27, 2015
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    I'd really like someone to just give me an educated guess as to what part number to use from the few meager voltage and amperage specs above.
    These little boards cost over a 1000.00 to buy. Coated in rubber and not meant to be repaired. Look to contain about 20.00 worth of parts.
    So if it doesn't work, no big deal. I can just buy the board and won't be out much for trying.
    Also I did find out It is a Fuji Electric 2SK**** in that To-247 size if that helps.
    Thanks in advance for your knowledge
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
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    I gave you an educated guess in post #2.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The 2SC3541 is a NPN power transistor and the D5LC40 a fast rectifier, presumably across the S,D of the 2SK mosfet.
    Many of the 2sk series are obsolete Mosfets, I would do a little reverse engineering and come up with a suitable N type Mosfet replacement from IR etc, based on the circuit and the voltages used.
    Max.
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    Several times now I've suggested the TS brush up on circuit symbols and so on.

    A 6A fuse was mentioned - the MOSFET should be rated for a safety margin - at least 50%, 100% would be better.

    Its obviously driving a highly inductive load, so far it hasn't been possible to coax out of the TS how any of the other parts are connected to the damaged device. There should be a back emf clamp diode in there somewhere - but who can tell!

    One slightly risky way to get the voltage rating is rig up a diode/capacitor peak detector in place of the MOSFET and flick a short circuit on the drain/source pads - that should provoke whatever back emf there is and allow a reading to be taken. Again. a generous safety margin would be in order.

    The risky bit is pumping unregulated juice into the exciter coil, will cause the generator to develop the maximum output it is capable of for short periods.
     
  12. kbxc20

    Thread Starter New Member

    May 27, 2015
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    Here's a couple of pictures of board from each side. On the six plug connector: The two left and two right pins connect to a dedicated open delta excitation winding, voltage will be 60 VAC or so. These connect to the two D5SBA60 SBRs- one for each side. The two center pins are the DC exciter output from the Regulator. Top round center pin is positive thru fuse to the SBRs (connected parallel). The bottom center pin is negative, goes to S lead on mosfet. Negative side of parallel SBRs connect to D on mosfet. As for the D5LC40 the center pin goes to the + and the two outer pins go to the - of the same circuit.

    The only other external connection is the two outer pins of the 3 pin plug -240 VAC measured and maintained by the Regulator.
    It powers up as far as the mosfet and will work the exciter winding as is, but of course has no controlling adjustment.
     
  13. MaxHeadRoom

    Expert

    Jul 18, 2013
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    IRFP260?
    Max.
     
  14. kbxc20

    Thread Starter New Member

    May 27, 2015
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    Sounds good to me.
    Thanks
     
  15. ian field

    Distinguished Member

    Oct 27, 2012
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    My gut says that part is over generous on current rating, I think a 12A part is nearer the mark. IMO: the voltage rating probably needs to be a bit more than 200.

    As its driving an inductive load, there's probably a back emf catch diode - I'd look up its voltage rating and copy that.
     
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