Matching ultrasonic transducer

[watches01]

Hello,

   I have a watch cleaning machine that i would like to rebuild before it goes bad. I'd like to at least change the capacitors on the ultrasonic generator board. I've read that the board has to be matched to the transducer or it will fail. On the older tube models I know you can just adjust them for maximum cavitation. This one is solid state (late 70's - early 80's). Is it enough to just listen to it and adjust it or should it be done with a scope? I don't own an oscilloscope yet but I will buy one if necessary. Can anyone explain how to do it with a scope? Any help is greatly appreciated. Thanks!

[Samogon]

I don't think that resonating frequency mismatch can do any hard except wasted money. I would pay attention to load capability. For instance transducer with higher power rating can overload output mosfets and as result burn them.

[watches01]

Thanks for the answer. I won’t be changing anything like that. I have two of these, one was rebuilt years ago and the ultrasonic is strong. I bought a second machine for a back up and it is weak so I never used it. I’m afraid it’s going to burn up like the first one did so I’d like to change the capacitors before it does. I just don’t want to cause more harm.

[Samogon]

If it is weak, that could mean that final amplifier stages are damaged, may be not power mosfets but driving preamp stage. But be carefull with oscillooscope, there could be hundreds of volts amplitude on final stage. It is safe to use handheld scopemeters like fluke 97 or fluke 123,124 they can measure up to 1kV with proper probes. This scopemeters can be not very expansive 97 can be around $100.
But if you plan to do electronics i would buy new rigol or siglent, but then you will have to get expansive high voltage probe.

[Armadillo]

Please don't have the wrong notion that changing the capacitors would solve your problems, furthermore most of the capacitors are film type capacitors like Polypropylene Capacitors.

The ultrasonic transducers are moving parts like speakers, don't expect them to last forever. It looks like a space capsule and can be bought even with bigger wattage, of course with matching driver board and the frequency you want.

The transducers [space capsule] have 2 connection [each] from the driver board which are "live", so don't accidentally touch on it. It needs to be loaded [not empty], otherwise it spoil easily. Measure the leads with a tong  / clamp current meter than a oscilloscope would be easier.

IMO, changing the capacitors would be a waste of money for you. 
I think the guy that rebuilt for you had done a fine job.

[Armadillo]

Or wound 3 or 4 turns around the leads and connect to the oscilloscope so that you can see if the frequency has drifted [out of tune].   

[watches01]

Thanks again for the responses. That’s what I’m wondering, has the frequency drifted and is it out of tune? I’m a beginner in electronics and I still don’t understand how to check that and I don’t know what the frequency should be. The place that fixed the first one is long gone. This is not a tank style cleaner with the horn, it’s an automatic machine with a drum style transducer that has a motor shaft running through it. The whole head goes into the jars of solution. It’s probably the same procedure anyway. I’d love to be able to maintain these machines myself.

[Armadillo]

Must be some expensive watch cleaning business. Is that a custom machine? So there must be a brand and model number?
Post some pictures of the board and the transducer / tumbler drum would be easier for discussion.

You can make reference measurement on the good cleaner frequency and current for the weaker one.

You can sure maintain these machines by first getting your hands dirty, I mean you need to dismantle it by your hands to study it.

Cheers; 

[watches01]

It’s a Tempo 400 made by L&R. I tried to post pictures but for some reason they won’t load from my iPhone. They are pretty expensive machines. I took one apart ten or fifteen years ago but I don’t remember much of it. I’m going to start on this one as soon as I can.

[Armadillo]

I can't visualize how "ultrasonic" is it. Even the operator manual didn't use the word ultrasonic. I have not seen one before surely.

If you do teardown, maybe you can capture it in video and be the first and only one in the world.

At the hindsight, don't look difficult.   

[stevelup]

the word ultrasonic appears dozens of times in your attached PDF!

[Armadillo]

I mean the title block   

Yeah, its ultrasonic. Maybe the video didn't press the ultrasonic switch.   

[Armadillo]

The ultrasonic frequency is designed at 100KHz;

You can tap the feedback signal from terminal 4 [Blue Wire] of the transducer mounted below the reversible motor and adjust trimpot R5 on the circuit board until somewhere around 100KHz, while your tong meter placed on the line of the driver board read maximum peak current [around ~4A peak, my guesstimation].

I do not recommend adjust R5 by visual and feel approximation    .

If not happening, then there could be some circuit problems.

I suggest you first do what you wanted initially. Change capacitors. That's what you can do without a oscilloscope.
There are 2 electrolytics which I think you like to change C3 and C4.

OK, hope it helps. We wait for your photos and updates.   

[watches01]

That’s exactly what I needed to know. Thank you so much for that information! I couldn’t find any information on this machine. Do I need high voltage probes to tap that feedback signal? I’m wondering if changing the caps will change the tuning, I’m guessing it would. This gives me a good excuse to order an oscilloscope and a clamp meter. Thanks again I really appreciate you taking the time to answer this!

[Armadillo]

The transducer driver circuit board is not isolated from the "Line" hence you "CANNOT" probe the board directly even though the feedback signal [transducer terminal 4 blue wire] is low voltage signal. You do not need high voltage probe. So either you
1. power the entire driver board with isolated power supply and probe the blue wire terminal directly
OR
2. Wrap 3 or 4 turns of magnet wire around the one of the wire leading to the transducer directly [not the blue wire] and connect this magnet wires to the oscilloscope.

At the same time;
At the transducer, there is a capacitor in parallel with the transducer which resonate with the inductance of the transducer. You need to check that this capacitor is OK. Failure of this capacitor is the loss of power even though the driver frequency is correct.

The 2 electrolytic caps are DC smoothing capacitors.

You know you will be dealing with lethal voltages and take safety precautions and also order safety gears like gloves and eyes protection etc.

I have a feeling that I am offending..... some people. 

I do not know if its worth to buy instruments to maintain this, but it will be sure a lot easier to let the "Experts" do it professionally for you.   

[watches01]

I bought an Isotap isolation transformer so I should be ok there. Ill start with those capacitors and see what happens, but I’d like to have the scope anyway so I’ll probably order one. Thanks again and I’ll keep you posted.

[watches01]

I had some time today so I started on the machine. It looks like there is only one electrolytic capacitor on the generator board and it tests ok with a peak esr meter. Tomorrow I’ll take it out and test it with my capacitor tester for leakage. If it looks ok then I think the next step is to order the oscilloscope and try to see if the frequency drifted for some reason. I did find that the large power transistor wasn’t quite as tight as it should be so maybe the ground connection isn’t quite there. I’ll change all the electrolytic capacitors on all three boards while it’s apart. I did find one bad one on the motor control board. I’ll also remove the orange drop cap that is in parallel with the transducer and check it, but I don’t think those usually go bad. If you notice the one film cap is unsoldered on one side it’s because I had to do that to test it. It didn’t test good in circuit but does test good out of circuit. Hopefully I can post the picture from my iPhone.

[watches01]

Nope. Last time it was the wrong extension. This time the file is too large.

[Armadillo]

[watches01]

Here's the board

[watches01]

Here's the schematic

[watches01]

I checked that electrolytic and it seems ok. I'll change it anyway, but I don't expect any different result from it. I also checked the .0039 cap in parallel with the transducer and it seems fine. It looks like R5 is a variable resistor in a small blue box on the board, but there is also some type of variable component toward the center of the board. On the schematic it looks like a transformer, but looking at it I see that it is adjustable. Is it possible that R5 adjusts the frequency and the other adjustment might affect the intensity of the ultrasonic? I don't want to adjust it without knowing what it does. I ordered a scope and I'll order the caps this week.

[Armadillo]

You can see the 2 spraque capacitors there. I like spraque, pretty good reliable capacitor.
You should unsolder them from the board and verify the ESR or DF.
BTW, What are you replacing them with?

R5 adjust the frequency.

[Armadillo]

1 of the spraque is the film type capacitor; you should also check it.

[watches01]

I’m going to see what’s available from Mouser and try to use quality components. That sprague film capacitor tested like it was open while in circuit. I desoldered one side and tested and it seems ok. I have an old Heathkit IT-28 and I checked it for leakage. Seems ok but I’ll change it anyway. Esr was good on both.