Uultrasonic cleaner trouble

[Averagesupernova]

TL;DR

Inexpensive cleaner is sensitive to amount of fluid in the tank.

I have had a Vevor brand ultrasonic cleaner for several years. I purchased it new. When I first purchased it I tested it out by filling the tank with water and turning it on. For about 30 seconds nothing happened but then it made the familiar buzzing noise and appeared to be working. As time went on it seems to take longer and longer before it starts buzzing.
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Yesterday i filled the tank and I basically gave up waiting for it to start. I popped the bottom off looking for poor connections and obvious problems but noticed nothing. Now I realize it's not advisable to do this but I turned it on without anything in the tank and it came to life immediately. I was surprised at this so I quickly shut it off. Thinking I had moved a poor connection I reassembled after hitting some questionable solder joints, filled with water and turned it on. It didn't buzz. At this point I recalled that sometimes it seemed like it would stop after adding the parts to the solution while running. I had always assumed this was likely a mechanical connection that moved as I dropped the part in. Well as it turns out it's not. If i put a small amount of water in the tank (much less than recommended) it immediately buzzes when turned on. If I add water it gets to a certain point and stops. Abruptly stops, not just steadily gets quieter. If I move the unit and let the water slosh around it will intermittently buzz as the water moves. It's as if more material in the tank kills the oscillation. Pretty sure these things don't rely on the fluid tank as part of the actual oscillator. Is plain to see the motion on the surface of the water when the unit buzzes and lack of motion when it stops.
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I run some parts through it today with less than recommended fluid just to get the job done. I see little difference in taking a chance on wrecking the cleaner and not being able to use it because too little fluid in the tank and not being able to use it because it just doesn't work with recommended fluid level. I detest poor quality tools and don't have the time to dissect it and determine what is happening. Wondering if anyone has had similar experiences with a Vevor brand cleaner. Google turns up very little other than units that release smoke, blow fuses, catastrophic failures, etc. I will likely replace it with something else but thought I'd share my experience in case someone has had something similar happen.

 

[Baluncore]

The ultrasonic transducer sits between the tank and a counterweight. The counterweight can usually be adjusted to match and work against the tank full of water. It may be that the mounting of the transducer or the counterweight has become loose or maladjusted. Check the mountings, and look for a tuning screw on the counterweight. That might need adjustment to bring it back in tune.

A heated cleaner will have a thermostat. The oscillator does not start until the water reaches operating temperature. Failure to start with high water level, may be due to a failing heating element or the thermostat.

 

[Averagesupernova]

I have not verified whether the device discussed in the video is identical to my unit but it is the same company. It does not surprise me that the unit in the video is designed the way it is based on the symptoms of my unit.
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This afternoon I allowed plenty of time for the unit to warm up before I turned on the ultrasound. No buzzing. I transferred the fluid out of the tank and poured in a half inch of plain cold water and the unit started right up. I added more water repeatedly killing the oscillations. I would rock the unit back and forth and it would restart. I continued adding water until it was to the required level. At this point I could turn the unit on and off repeatedly and it would restart every time. As I was going about my work the ultrasound shut off after the set 20 minutes. It probably sat for another 20 minutes before I tried restarting it successfully. Tomorrow I will return to a cold unit that will quite likely not start and I will need to go through the whole process over again. Assuming the schematic is very similar to the one in the video I'm betting there is an issue with one of the capacitors in that capacitive divider right off the power supply. I may not fiddle with that any time soon. I can't see that it makes any sense to buy another one either as I expect poor quality in one form or another.