Failed 750 ml Chinese Ultrasonic cleaner - Page 1
Forum section: electronics / beginners

author: Machinist60
author_rank: Newbie
timestamp: February 04, 2022, 06:02:13 pm
content: I am a complete newby with this stuff. I had some intro to electronics in physics at university 60 years ago and worked around airborne digital data acquisition systems for geophysical survey processing data for much of my professional life.I have this failed ultrasonic cleaner from Harbor Freight CD-7820(A). It has a 50mm diameter 43KHz 35W Piezoelectric Ceramic Transducer Plate glued to the underside of the tank as in attached picture. Visual examination of the PCB and components shows nothing unusual.Can someone enlighten me as to what the expected voltage and waveform might be driving the transducer. I don't want to expire or release magic smoke.Thanks.

author: radiolistener
author_rank: Super Contributor
timestamp: February 04, 2022, 06:24:35 pm
content: most of all piezo transducer is degraded or output transistor is burned out. This kind of fail is typical for ultrasonic humidifiers running on 2.3 MHz. So I think your cleaner has some similar fail.

author: SeanB
author_rank: Super Contributor
timestamp: February 04, 2022, 06:48:46 pm
content: Normal failure mode is the transistors go short circuit, blowing the input bridge rectifier and then finally the heatshrunk fuse. If no display look at C4, likely failed open circuit, stopping the capacitive power supply from working, meaning no results. The little relay also can burn open, cheap enough to replace as well.Killer for them is the transducer failing, either cracking to pieces, or the connection under that glue burning off. You can buy them though as a bare disk, solder wires onto them, and then use a 2 part epoxy, like Araldite regular, to attach them to the bath, making sure both surfaces are grease free before by wiping down with some acetone. To remove old one heat gun and warm to 300F, which will degrade the epoxy and cause it to soften ,allowing you to scrap it off. Then sand the area with 180 grit wet and dry paper before attaching the new one in the same place.

author: free_electron
author_rank: Super Contributor
timestamp: February 04, 2022, 07:23:06 pm
content: CRACKED ?

author: radiolistener
author_rank: Super Contributor
timestamp: February 04, 2022, 08:07:32 pm
content: I don't know what is the reason but ultrasonic transducers working at high power (5-10 W and more) are going to lower and lower power after some time and at some moment they cannot produce enough power sound. They don't have any sign of crack, just like new but works very-very weak. May be microdamage inside or something like that. For ultrasonic humidifiers you can buy replacement transducers on aliexpress.You can try to find replacement on aliexpress, but you're needs to know resonant frequency and power.

author: coppercone2
author_rank: Super Contributor
timestamp: February 04, 2022, 08:26:17 pm
content: keep in mind those transducers like to delaminate from the tank too. I had to reglue mine with JB weld but I ended up getting a better ultrasonic cleaner because that thing had more problems then I have fingers.the ultrasonic head falls off the harbor freight tank and starts melting itself through the bottom of the chassis like a dead alien

author: Machinist60
author_rank: Newbie
timestamp: February 05, 2022, 04:23:09 pm
content: Thanks for the replies guys. I have ordered new transducers from Aliexpress, now the wait.

author: coppercone2
author_rank: Super Contributor
timestamp: February 05, 2022, 05:02:15 pm
content: if you need to reglue it, I used a 220 grit dremel flap wheel and JB weld to glue it and it survived for 2 years of fairly regular use before the electronics got screwed up and it got replaced. factory job failed in like 2 hours of use.

author: Machinist60
author_rank: Newbie
timestamp: February 05, 2022, 10:05:07 pm
content: The good advice on removing and re-gluing the transducer is appreciated, thank you.