What Do I Do Now?

Discussion in 'The Projects Forum' started by tcawley29, Mar 6, 2013.

  1. tcawley29

    Thread Starter Member

    Jan 23, 2013
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    Okay, so I think I have a damaged diode and transistor on a treadmill circuit board.
    I would like to replace them but I have a problem.
    There is no markings on the transistor or the diode to tell me anything about them so that I can order new ones.
    Here is a picture of them. Slightly blurred but that doesn't matter because there isin't any writing to read.
    Thanks
     
  2. bance

    Member

    Aug 11, 2012
    315
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    Look for a schematic? That'll give you the part numbers you need.
     
  3. tcawley29

    Thread Starter Member

    Jan 23, 2013
    47
    0
    After checking, the diode is fine. The transistor is the problem. I'll try and find a schematic but knowing my luck I won't be able to :(
     
  4. tcawley29

    Thread Starter Member

    Jan 23, 2013
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    0
    Nope can't find a schematic. Any ideas which transistor I could try. Board runs off 240 volt mains and powers a 180 volt motor. Treadmill is a Discovery T1700
     
  5. bance

    Member

    Aug 11, 2012
    315
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    None whatsoever....

    Good luck.
     
    tcawley29 likes this.
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
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    step 1- take a couple of blurry pictures
    complete...:p
     
  7. tcawley29

    Thread Starter Member

    Jan 23, 2013
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    0
    I tried my best with it, I have shakey hands.
    When I test the transistor labelled Q8 on the board I get a reading of 0.706 between the outside left and outside right pins. I don't get any reading off the middle pin. Does this mean the component is fried.
    I will take new pictures if ye need me to.
    This component is connected to the negative terminal of a 180v DC motor.
    I get a reading of 0V when I measure between the M+ and M- terminals.
    I think this transistor is the reason for this.
    The treadmill is plugged into 240V mains.
    Which transistor do you think would be a suitable replacement.
    There isin't any writing at all on this one.

    Thanks
     
  8. tcawley29

    Thread Starter Member

    Jan 23, 2013
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    0
    Just found the board number: MT03B04H
     
  9. bance

    Member

    Aug 11, 2012
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    If the treadmill is plugged into 240V mains, you shouldn't be probing around inside it, at least not if you want to use it again!

    Be very careful with mains power, it bites....

    If you want help you are going to have to make an effort, no-one is going to search the board numbers, or the model numbers, you have to do it!!!
     
  10. tcawley29

    Thread Starter Member

    Jan 23, 2013
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    I have nothing to lose as parts can't be bought for it.
    I looked up the part number on google and only one result came up.
    Apparantly someone with a raleigh treadmill had the same problem.
    Mine is a discovery treadmill.
    Discovery are gone out of business. I couldn't find a proper website for raleigh treadmills either. Just one about bikes.
    I'm at a loss as to what I should do.
    When I test the transistor I only get a reading using the two outside pins using a multimeter in diode mode. I can't get a reading using the middle pin.
    I would love to try and replace the part but cannot find out what to replace it with because there is not any writing on the transistor.
    I am willing to test voltages and current using live mains if I have to for finding a suitable replacement.
    I just want my treadmill back working again!!!
     
  11. tcawley29

    Thread Starter Member

    Jan 23, 2013
    47
    0
    Or would bypassing the transistor accomplish anything. If so how would I go about doing it
     
  12. bance

    Member

    Aug 11, 2012
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    I think I've already warned you about messing with mains power.

    If you want to DIY do the research, otherwise it's time for a new treadmill, or order a box!
     
  13. tcawley29

    Thread Starter Member

    Jan 23, 2013
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    0
    Yes I understand the risks. I am trying to do the research. I cannot afford a new treadmill
     
  14. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
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    There is no guarantee this is a transistor. It could be a TRIAC or a MOSFET.

    Show the complete PCB from both sides in good resolution.
     
  15. tcawley29

    Thread Starter Member

    Jan 23, 2013
    47
    0
    Here ya go. The rough part near where 110 is where a varistor had blown so I removed it.
    Thanks a million,
    I would love to get this fixed
     
  16. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    Hmm. From the PCB we can see where is the gate or base signal.

    WE don't need the full schematic, but information about the connection from the storage cap to the transistor. Which polarity?

    If we know that we can measure the base (or gate) signal when the circuit is powered up.

    From what you write I assume it is DC regulation circuit.

    Once you know if N-channel or P-channel, you can simply try a large overdimensionated replacement. Most will somehow work if the voltage rating is good enough.

    MOSFET and BJT are exchangeable for some kind of circuits, not if it is a BJT circuit with only 1V base drive.

    You'd have to order some devices to try eventually.

    And information about the motor is needed (how many Amps under load). Is it possible the motor can be loaded heavily or even may stall? Startup current for motors can be 8x times higher.

    This is where the problems may come from, startup current, and currents under high load.

    If the rest of the circuit is not damaged, it should be possible to make it working again with relatively little investment. Don't forget fresh thermal grease.

    Maybe even put the transistor on a seperate board with a better cooler (I think of VGA coolers here running from 12V).

    Since the base (or gate signal) is known this does not leave open so many possibilities for testing. I assume the transistor is broken anyway. Do you have a test circuit for transitor or MOSFET?
     
  17. tcawley29

    Thread Starter Member

    Jan 23, 2013
    47
    0
    Sorry for souding stupid but what exactly are you calling the storage cap?

    Yes I think it is DC current. It is definately a 180V DC motor.
    I can check for further details on the motor tomorrow after college.

    The rest of the board is free from damage.

    All of these problems occured when an overweight family member used the treadmill. They were at least 10-15KG over the maximum weight.

    I have a small section on my multimeter labelled: e c b e. I assume this is for inserting transistors.
    This is my multimeter I am using: http://www.ebay.ie/itm/Professional..._Measurement_Equipment_ET&hash=item1c262f2f41

    Thanks
    Thomas
     
  18. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    The large black capacitor. To know the connection to the transistor would mean eventually we can figure out about it's technology (PNP or NPN).

    PNPs normally are connected to +/Vcc, and the load is between the transistor and ground.
    NPNs connect the load to ground, while it is connected to Vcc.

    From the rectifier I do not think there is more than 3A permanent current.

    Can you order components from Farnell? They have many power transistors. Or do you use eBay? They are often more expensive on eBay.

    Don't try to desolder the power transistor, so-called via's are easily destroyed by this. Simply cut it off, it is no problem to solder on top of the wire remains.

    The pin on the left side would be the base (the others have thicker traces).

    It is also possible they use a SCR or Thyristor here, don't know about the schematic.

    More likely, I guess it is a PWM regulator. Can you read anything on the IC on the right side?
     
  19. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    The "transistor" shorted or not wouldn't likely be connected across the motor.
    It appears from the pictures the diode may be connected across M+ M-
    but it's hard to tell for sure.
    You said the diode test's good - what are the two meter readings?
     
  20. patricktoday

    Member

    Feb 12, 2013
    157
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