Cheap ultrasonic cleaner doesn’t work anymore

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

the large transformer has fractured solder joints.

Tried resoldering them but no difference

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

So I tried another ic and the result is the same as before

[R_J]

Re: Cheap ultrasonic cleaner doesn't work anymore

There are only a few components, The ic drives the two fets, they switch on and off at around 40khz. The output drives the piezo. the output signal goes through the transformer winding (the one with the resistor in parallel) the other winding provides a small sample of that signal back to the ic via the control. It does look like the control is used to fine adjust the frequency.
Check C20 & c22, and the 3 resistors next to the control, check the control also.

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

There are only a few components, The ic drives the two fets, they switch on and off at around 40khz. The output drives the piezo. the output signal goes through the transformer winding (the one with the resistor in parallel) the other winding provides a small sample of that signal back to the ic via the control. It does look like the control is used to fine adjust the frequency.
Check C20 & c22, and the 3 resistors next to the control, check the control also.

Thanks I'll check them. How is the output voltage generated? I'm used to fets switching a transformer to create output voltages but you're saying it's only used for sampling.

[R_J]

Re: Cheap ultrasonic cleaner doesn't work anymore

I do believe that is how the transformer is used, the piezo is driven directly. I did a paint schematic of that part of the circuit.

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

I do believe that is how the transformer is used, the piezo is driven directly. I did a paint schematic of that part of the circuit.

Thanks for that. The resistors test good. The caps aren't shorted and seem ok. Not sure how else to test them with just a multimeter.

I'm wondering if it's an issue with the control side where you set the duration you want it to run. I noticed sometimes not always the counter will glitch when counting down. But idk if that's related to the piezo not being turned on causing it to behave that way.

Anyway to turn the circuit on for testing without the display control?

[R_J]

Re: Cheap ultrasonic cleaner doesn't work anymore

The ultrasonic portion of the circuit is turned on or off by the relay, thats it. The two elec. caps (near D10) along with D10, D1, & C10 form a voltage double (328vdc) that feeds R3 which connects to one contact of the relay, the other contact connects to the (328V) in the schematic.
The 4 diodes below the relay are the bridge for the low voltage, C5, R4, C7 are the filter. C7+ supplies the relay coil, Q1 switches the coil on or off from the top board.
D13 is likely a zener which is on the base of Q2 which is used as a regulator for the (5v?) to the top timer ic/circuit.

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

So after trying everything do you think it’s not fixable?

[R_J]

Re: Cheap ultrasonic cleaner doesn't work anymore

So after trying everything do you think it's not fixable?

It worked before, so something changed. I see the ends of the wires (under the glue) on the piezo, look black,maybe they are no longer attached to the transducer.

You might be able to check if there is any ac voltage across the transducer. Check if there is any AC voltage across C16 when you turn on the unit. The frequence will be high (40khz) so your meter might not see it. I would think you should be able to see a couple hundred volts AC

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

At the circuit board, across the wires going to the piezo it briefly shows 115vac before it drops off

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

It worked before, so something changed. I see the ends of the wires (under the glue) on the piezo, look black,maybe they are no longer attached to the transducer.

You might be able to check if there is any ac voltage across the transducer. Check if there is any AC voltage across C16 when you turn on the unit. The frequence will be high (40khz) so your meter might not see it. I would think you should be able to see a couple hundred volts AC

I pressed on the connections at the piezo and it turned on. Good catch on possible bad connections. I tried resoldering them but the wire on the side (on the black) started arcing and stopped working

[R_J]

Re: Cheap ultrasonic cleaner doesn't work anymore

So the connections are bad on the piezo, you might be able to solder on them but you need to be carefull, too much heat and the ceramic piezo will crack.

[stj]

Re: Cheap ultrasonic cleaner doesn't work anymore

you need silver solder or you will just destroy the layer on the piezo

[R_J]

Re: Cheap ultrasonic cleaner doesn't work anymore

The melting point of silver solder is way too high, Use regular solder and be very quick and do not keep the iron in one spot or you will damage the piezo

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

Thanks for the info. As I was trying there was a square tab on the side that the wire was soldered you and it broke off. Not sure if this was the original fault and when trying to fix it made it come off completely. Can this be fixed?

[stj]

Re: Cheap ultrasonic cleaner doesn't work anymore

the layer on the piezo is deposited silver,
the point of silver solder is to prevent migration of the layer into your solder!!

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

Thanks for the info. As I was trying there was a square tab on the side that the wire was soldered you and it broke off. Not sure if this was the original fault and when trying to fix it made it come off completely. Can this be fixed?

Not fixable at this point?

[R_J]

Re: Cheap ultrasonic cleaner doesn't work anymore

Not fixable at this point?

I can't see it, Got a picture?

[caphair]

Re: Cheap ultrasonic cleaner doesn't work anymore

I can't see it, Got a picture?

Yes. It's hard to see but there's a very small bit left sticking out. I tried Soldering the wire to it but didn't seem to take.

[R_J]

Re: Cheap ultrasonic cleaner doesn't work anymore

I don't know how you you could even get at the bottom to resolder the connection, the top is also bad, It seems like the glue did most of the damage to the piezo. You can likely solder the top wire to a different spot to make a proper connection but thats not going to help if the bottom is not connected.