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In article , (Fred McKenzie) wrote:
In article .com,
"nortonfan" wrote:

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.

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.

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.

greg