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ultrasonic cleaner not working

Discussion in 'Electronic Repair' started by nortonfan, Apr 6, 2006.

  1. nortonfan

    nortonfan Guest

    I'm attempting to bring my Bulova model TR250 ultrasonic watchmaster
    cleaner back into service. I have found two rectifier diodes blown,
    along with the circuit protection fuse. The wafer transducer is epoxied
    to the the tank, and I am not sure how to go about testing for
    problems. It appears to be solidly mounted to the tank with no visible
    fractures to the epoxy joint. However, I suspect there is a problem
    with it, as it has lost its cleaning abilities. This model seems t
    have been made in the mid '80s.

    Thanks for your help!
  2. Scott Lane

    Scott Lane Guest

    I would replace the semiconductors and try the unit out. It will probably
    work. If it continues to blow fuses/eat diodes then you will have to
    troubleshoot further. Scott
  3. NF-

    Are you familiar with crystal oscillators? That is roughly how the
    ultrasonic transducer is connected, but as a high power oscillator. The
    remainder of any electronics would be for a timer/controller.

    The transducer probably has a ceramic element, and is constructed somewhat
    like a capacitor. It should have electrodes fired and/or plated onto
    opposing surfaces, one of which may be glued to the bottom of the tank.
    One failure mode would be a fractured ceramic. You might check it as a
    capacitor to see if it is shorted or leaky.

    I don't know how practical this would be, but one test might be to connect
    the transducer to a sensitive oscilloscope and see if mechanical
    vibrations result in electrical waveforms.

    Be sure you always have a liquid in the tank when testing. Unloaded, the
    transducer is more likely to fracture.

    When you get it working, you should wear hearing protection while it operates.

  4. GregS

    GregS Guest

    Also use fluid!
    I would use a lamp connected in series with line in after replacing components.
    I worked on a fairly complex model a while back and gave up because
    I didn't have enough documentation. The circuit will usually either work or not,
    but in my case just refused to generated enough power. The frequency
    and resonators must be right on value. The transducer must match
    the opperating frequency of the oscillations.

  5. nortonfan

    nortonfan Guest

    Thanks for the insight, Greg. I'll try to set something up for
  6. nortonfan

    nortonfan Guest

    Fred, thanks. Your suggestions will be followed.

    I just didn't want to replace the fuse and blown diodes and power the
    thing up not knowing what to expect. Just before the fuse an diodes
    went out, it was making its "normal," low frequency/volume buzzing
    sounds. Naturaly, I could not hear the high frquency stuff but parts
    were getting somewhat cleaned.

  7. I used to repair ultrasonic cleaners back in the 70's.
    The most common problem was the transducers becoming partially unglued
    from the tank. I always assumed stuff had been dropped into the tanks,
    but perhaps the ultrasonic energy caused it.
    I used to pry the transducers off the tanks and then glue them back on
    with a silver-loaded epoxy. This usually worked and was quicker and
    cheaper than a new tank assembly.
    I would usually test the generators by substitution with a good unit,
    something you can't do. If they needed repair I would run them with a
    resistive dummy load, but I can't remember what value it was.
  8. nortonfan

    nortonfan Guest


    Silver-loaded epoxy? Was this part of the composition of the epoxy
    type, or was it something added into the mix during application?

  9. Norman-

    I don't know, but would expect it to have been part of the composition. I
    believe the silver is needed to provide electrical connectivity to the
    transducer, but it might also serve the purpose of making a more rigid
    attachment between the transducer and the tank.

    I wonder if any service information is available from Bulova?

  10. nortonfan

    nortonfan Guest


    I searched for silver charged epoxies and did find several types. I've
    also searched the web and found no contact information for Bulova
    ultrasonic cleaners. There is an address, however, for the watch line.
    Before I began taking a screwdriver to it, I wanted to have a firm
    understanding of its operation and a realiable source for parts.
    Thanks to fellows like you, this job is not as daunting as I once
    envisioned. However, I still have no sources for parts nor significant
    technical information on this particular unit. A similar unit to the
    one I have is presently on Ebay for well over $200 and will probably
    exceed that, considerably, during the feeding frenzy of the last
    minutes of auction.

    I've replaced the blown diodes and the protection fuse and powered the
    unit. It makes a rather annoying buzzing sound, not as loud as an old
    doorbell buzzer - but, annoying, nonetheless. My concern is that if
    the epoxy joint has cracked (though I have not seen any cracks), this
    would lead to failure of the transducer. I would prefer to prevent
    this possibility and, at the same time, I'm a bit gun-shy of tampering
    with it for fear of making things worse. The old wisdom of "if it
    works, don't fix it." Maybe, it's supposed to make the buzzing sound?

  11. That buzzing sound may be normal. These things are far from silent
    and the ultrasonic waves are often not CW. Have you tried anything
    in the tank? I assume you had water in the tank at least.

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  12. Norman-

    If the power rectifier diodes were blown, I would suspect that any filter
    capacitors associated with the output of the diodes might have also been
    damaged. Obviously they aren't shorted, or you would have blown more

    As you have noted, Bulova is a watch company. They may have had some
    other company make the ultrasonic cleaner for them. A little research
    might turn up two or three companies that have produced them, and there
    may be a model that looks identical to yours.

    Back in the 70s I built the Heathkit GD-1150 Ultrasonic Cleaner. The
    operational test was to use a 1" strip of aluminum foil held vertically in
    1" of water, and expect a minimum of ten pinholes created in the foil
    after 30 seconds of operation.

  13. The silver was in the epoxy, it made the epoxy electrically conductive.
    The transducers were like a big ceramic capacitors with metalising on
    both sides. I seem to remember that when the transducers became detached
    some of this metalising came away from the transducer. Using the silver
    loaded epoxy to re-attach the transducer fixed this as well. I remember
    talking to a bloke at Araldite about it. They made a specific product
    for this application but it was not readily available in small
    quantities, so we used a similar product from RS Components. (Also made
    by Araldite.)
    I've had a look at the RS website but I can't see the product I used, it
    was 30 years ago! they do list a silver loaded product but it seems to
    be American. Araldite have long since shut up shop in Birmingham (UK).
    It may well be an abandoned technology by now. The electronics industry
    was a big user or ultrasonic cleaners, but its all "no-clean" stuff now
    (and all gone to China!)
  14. nortonfan

    nortonfan Guest

    Hi guys!

    To all of you who replied to my questions, thanks! My ultrasonic
    cleaner is working within its capabilities and I'm very pleased that I
    did not blow anything up, including myself! Most of it, thanks to you
    guys. I learned something about how ultrasonic cleaners operate,
    cleaning solutions and, most of all, the valuable resource and support
    this forum provides.

    Norman C
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