Anyone familiar with ultrasonic generators?

Discussion in 'The Projects Forum' started by soldersplatter, May 29, 2013.

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  1. soldersplatter

    Thread Starter New Member

    May 29, 2013
    Anyone familiar with ultrasonic generators? I'm hoping someone here knows which components typically fail inside the generator.

    These 20kHz generators are rather basic Chinese units (see pictures) used for welding nonwoven plastic (basically thin plastic fabric). I have a good/working unit and a bad/failing unit so in theory I should be able to compare good versus bad components. Both sets of converters and horns are fine since the good generator can drive both sets.

    Any constructive input is appreciated.

    Also, if there's a better forum to ask this question please let me know

    FYI - I'm no electronics expert: I have previously monkeyed with picBasic and 16f88 chips but that's about it.



    arunpradh likes this.
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    I don't know what level of electronics you have so don't be offended. i start with
    1) fuses (two next to the fans), power switches and internal relays (if any)
    2) transformer and rectifier and stable rectified voltage
    3) loose wires/connectors - make sure there are no missing screws that allow any board/component to short to chassis.
    4) dark/burnt looking components
    5) then i look for poorly made solder joints
    6) check all external cables - make sure I test everything external (including cables) on a known, 'good' unit if available.
    I rarely have to get to the last stages where I check all silicon chips and transistors have reasonable voltages.
    Last edited: May 29, 2013
  3. wayneh


    Sep 9, 2010
    How do you know it's failing? I'm not doubting you, just thinking there may be clues in its behavior.
  4. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    Compare the voltage test points is a good place to start, can you get the circuit diagram?
  5. Andreas

    AAC Fanatic!

    Jan 26, 2009
    Like GopherT put it. Use a logical diagnostic approach to your fault finding method, moving from the very obvious and simple things to the more complex within the chain.

    You state that the 2nd unit is "bad/failing". Does this mean that it is doing something, anything at all when you press the on switch?

    Please elaborate on what the converter and horns do. Is the horn a particular type of hand piece which welds the two plastics together.

    Do you have a user manual (any contact details in there)?
    You might be able to get the cct schematic from the manufacturer by doing an internet search. After all you have the make, model and serial number.

    The more information and details that you can supply (no matter how trivial) will help others to assist you.

    Great pictures by the way.
  6. soldersplatter

    Thread Starter New Member

    May 29, 2013
    Firstly, thanks for everyone's input.

    The problem was/is located on the board circled in green below. Swapping the board from the good/working generator allowed me to locate the problem. Board is essentially rows of transistors (C4237) and resistors. Now I just have to track down the bad transistor.

    fuses ok, no missing screws, no dark/burnt components, solder joints appear ok

    working unit vibrated the ultrasonic horn (welds plastic using vibration), failing unit didn't

    Dodgydave, Adreas
    Circuit diagram, User manaual? I wish I had both of those...



  7. GopherT

    AAC Fanatic!

    Nov 23, 2012
    On your last (bottom photo) the round resistor second from right on the top row is out sorts. It appears that the resistor lead closest to me is shorted to the transistor base pin.

    Edit: I guess that shouldn't matter since the pcb traces are connected. Maybe a previous attempt to fix the board?
  8. GopherT

    AAC Fanatic!

    Nov 23, 2012
    None of the resistors are paralleled. You could test them all in place just to be sure you don't have one failed as a short before you start with the silicon.

    Also make sure none of the collector (center pins) are shorted to the heat sink.
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    Standard technique is to lift one leg of each resistor, then test all resistor ohms. That will identify bad resistors.

    And after the larger resistors are lifted, the emitters of each transistor are now disconnected, so you can test each transistor with a multimeter for C-E short, which will be your most likely fault on high power banks of transistors.

    Or, just test the resistors and replace all the transistors. It might cost $30 for the 12 new trannies but the job will be done quickly, and done right.
    GopherT likes this.
  10. Ali Baba

    New Member

    Apr 24, 2011
    usually the high power transistors fail so best will be to take them out of the pcb and check them for open or short
  11. BR-549

    AAC Fanatic!

    Sep 22, 2013
    Compare voltages on boards. That should tell you which rail is bad. Of course, it could be both.
  12. arunpradh

    Active Member

    Dec 11, 2013
    did your deviced worked? i have a damaged one operates on same frequency needs help. the switching transistor is 2sc5570. i am planning to design one with igbt. can you provide any help?
  13. Lestraveled

    Well-Known Member

    May 19, 2014
    This thread is a year and a half old.
  14. bertus


    Apr 5, 2008
    closed due to old age
    arunpradh likes this.
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