Noob Help! Circuit Repair, components.

Discussion in 'General Electronics Chat' started by Tyler Durden, Nov 16, 2014.

  1. Tyler Durden

    Thread Starter New Member

    Nov 16, 2014
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    Hello Everybody,
    This is my first post, I'm looking for a long term place to lurk so I am glad to find this site. I'm getting into small electronic projects but this time I have a stressful repair for myself that popped up and need some help.

    I have an industrial printer, I went to turn it on and there was no power at all. I replaced the main fuse cause it was burnt out and then the power resister fried as soon as I plugged it in.

    I need to get this thing back up and running, so I can work.

    The other problem I found with my meter was a bad transistor. I don't know what caused the problem but I suspect the printer turned on for a self cleaning over night and it is possible a servo motor was stuck and blew something. That's all I can think could of happened, because it worked perfect the day before.

    Anyhow, Im trying to replace parts and fix this thing.
    My questions are, what is the best replacement for the burnt resistor. I can't find an exact, See pic, I don't want to cause more damage.

    The transistor pictured is hard to come by, what would be a good replacement spec wise? What else should I check for, I'm very worried other parts are fried or when I put it back in It could break again or damage another board. This printer has like 5 circuit boards. Its a large roland 545ex.

    I'm not good at testing, I just happen to be lucky to find the bad transistor when compared the the same one next to it. This is the power board for the printer.

    Any help or suggestions welcome. I tried to find a local tech but all that you can find now are ipod repair places.

    Thank YOu

    Capture 1.JPG Capture 2.JPG
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    The transistor is a mosfet 2SK2915 (see attached datasheet).
    (the 2S is often not printed on them).
    The resistor will be 10 Ohms (as in the yellow package).

    You might also want to have a look at this link:
    http://www.repairfaq.org/samnew/printfaq.htm

    Bertus
     
  3. Tyler Durden

    Thread Starter New Member

    Nov 16, 2014
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  4. bertus

    Administrator

    Apr 5, 2008
    15,645
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    Hello,

    A higher wattage of the resistor will never do any harm.
    The resistor will be able to dissipate more than the original one.
    As for the fets, they are comparable to me.

    There can be more parts defective, as parts do not blow without a cause.
    Have a close look at the capacitors, they may cause problems due to old age.

    Bertus
     
  5. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,773
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    If you haven't already done so, check all the electrolytic caps for bulges/leaks and replace any suspect ones.
     
  6. Tyler Durden

    Thread Starter New Member

    Nov 16, 2014
    3
    0
    Thank you, BTW the board is about 7 years old. The caps look pretty clean.

    Is there anyway to know why the Resister burnt up after fuse replacement, or where to look, Could that transistor be the cause. I'm bummed that the fuse did not blow the second time, I even put a 5A in instead of the 6.3 and it just fried the Resistor. Maybe I should have put a fast blo
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Quite likely. The next question is "Why did the transistor fry?" ;).
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
    782
    What you need to worry about; is whether that resistor senses a current, maybe a chip senses the voltage developed across it - when that resistor blew, it probably took the chip with it!
     
  9. wayneh

    Expert

    Sep 9, 2010
    12,093
    3,030
    And then replace the rest. I just repaired a board that did not have any caps that looked bad by visual inspection. Then I used an ESR meter (a simple DIY one I built). About half the caps on the board had an ESR that was MUCH higher than the fresh replacements, like 40Ω versus 1Ω. Replacing every electrolytic on the board cost all of $5 and now it's fixed.
     
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