Bulova Ultrasonic Watchmaster Issue

Discussion in 'Horological Tools' started by musicmike927, Jun 14, 2012.

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  1. musicmike927

    musicmike927 Registered User
    NAWCC Business

    May 10, 2011
    I bought a Bulova WT watchmaster at an auction about a month back. I cleaned it up, put in new tubes and got it working for short testing periods, However yesterday I noticed when cleaning my first watch with it, that when I turn the left (clean) ultrasonic cup on, after a minuet or two of operation, the fuse blows. This doesn't happen with the right (rinse) ultrasonic, which I ran for well over 6 minuets. I know it is not an issue with the cup as I've tested that theory.

    Are any of you familiar with these units and this issue?

    My hope is a faulty tube, though Im worried it could be something more pricey.

    Thanks, Mike.
  2. glenhead

    glenhead Registered User
    NAWCC Member

    Nov 15, 2009
    Telecom Engineer
    Williamson County, Texas
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    If it were mine, I'd open the case and compare the circuits to each other. Look for frayed/cracked insulation on the wires, an obviously cooked capacitor, that sort of thing. This is one of those times when a sniff test can tell all - you can frequently smell a cooked component. If nothing leaps out, try swapping the tubes to see if the trouble follows. If it doesn't, there aren't that many discrete components to replace - a couple of resistors and capacitors, according to the schematic. Good luck!
  3. neighmond

    neighmond Registered User

    Jan 31, 2003
    Horologist, Teacher of Horology
    Rural Iowa
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    Lots of things are in your favor here. This machine is built like a brick backhouse. It was designed to be serviceable, and has a straightforward design and clean, uncluttered chassis. With the exception of the selector switch, power transformer, and ready-made transducer coils, parts are available for it. Plus, most of your troubleshooting is done, because the problem only manifests downstream from the selector switch on the left side, and there isn't a whole lot in this short stretch of real estate.

    First look at your burnt fuse. Is the fuse a fast blow or slow blow? Fast means the wire is splattered all over the inside of the fuse, slow means the wire is simply melted through.
    Fast would most often indicate a short circuit somewhere downstream of it. This could be caused by failed insulation on one of the wires or components or shorted capacitor. Also, check the sockets of the tubes for carbon build-up between the pins, and if present replace the socket. Also look for a shorting transducer coil or short between the core (on the base of the cleaning cup) and transducer.

    A Slow blow is usually more indicative that the machine is demanding more juice than is good for it. Failed resisters can cause that. So can a loose connection, which might act like a resistor.

    There are two paper wrapped capacitors behind the tube sockets and two big fat ones on the bottom of the chassis. If it still has its original capacitors, replace them with something modern. Aside from the power cord the capacitors are the most disposable part in this machine, tubes included. Check resister values and replace where badly out of spec.

    The tubes operate in tandem, so a problem with the physical tubes and/or their driving circuit will probably act the same regardless of which transducer is energized.

    The selector switch is actually multiple switches on one shaft-the topmost section (right under the knob) powers a common bar under the transducer coils, and is closed in the right two positions. It has a failsafe in series with it which kills power to the bar if either of the vessels are not seated fully. The next one down energizes a relay located on the underside of the chassis next to the transformer of the machine, and that changes which transducer is powered up; the relay only closes in the far right position (rinse). The lowermost section powers the tubes, and is closed in the right two positions (wash, rinse.) While failure of this assembly isn't really common, it would bear looking into since the fault only manifests in one switch position.

    The selector relay is a single pole, double throw affair, and when not energized the wash (left hand) cup is active.

    The transducer coils are held in by a removable plate over each unit, and are decently heavy wire wound round a stamped metal core, and if one had to they could rewind one by hand, although they would be unlikely to enjoy it.

    The transducer leads (as well as the tube cap leads) are run through the pin holes of an octal socket on the chassis right behind them and under the tubes. They are met below by a common joint leading to a capacitor on one side, and the relay on the other. Because of your symptoms I would start looking on the relay side, because they separate at that point.

    My bet would be on a short somewhere in the left hand transducer coil, its leads, or perhaps the selector switch assembly. After checking that try the relay.

    Good luck!

  4. Richard1079

    Richard1079 New Member

    Jul 4, 2019
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    Anyone have coils for the WT model?
  5. brian fisher

    brian fisher Registered User

    Jan 20, 2017
    houston, tx
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    do you have any idea how old it is? i just picked up three ancient ultrasonics. they are old enough to use a single tube(not 2). they are not bulova. if there are any parts i can supply from my 3rd machine(which also blows fuses), i wouldn't mind helping you out.

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