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.