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!

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
"nortonfan" wrote in message
oups.com...
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!

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.

Fred

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

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

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.

Cheers,
Norman

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.



In message .com,
Nortonfan writes
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!


--
Neil J. Harris

Neil,

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

Thanks,
Norman

In article . com,
"nortonfan" wrote:

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

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?

Fred

Fred,

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?


Thanks,
Norman

"nortonfan" writes:

Fred,

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?

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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In article .com,
"nortonfan" wrote:

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.

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
diodes!

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.

Fred

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!)


In message . com,
nortonfan writes
Neil,

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

Thanks,
Norman


--
Neil J. Harris

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.

Cheers,
Norman C