Grundig UC6620

The Grundig UC6620 ultrasonic cleaner is a 35W cheap device with a lot of failure points.

Faults I had to repair in my unit were:

• A broken transducer
• Shorted driver transistors (IRF830 500V NFET)
• Shorted rectification diodes from the second discrete rectifier in the circuit, that's before the driver
• An open 0.1 Ohm resistor coupling the rectified voltage over to the driver transistors. The damage was not visible!

Fault description	image of Fault
Fractured/broken ceramic piezo electric transducer	The destroyed transducer after removal
Open circuit resistor coupling the rectified voltage to the driver	Burnt on the underside and invisible when installed. Make sure to measure these resistors.
The main PCB where the main driver transistors are very prone to dying. The Driver chip seems to be very robust as it retained no damage during a lot of failing attempts at restarting. The Diodes of the full bridge rectifier driving, supplying the output can go short too. They're 1N4007 standard diodes.	Mainboard with all repairs done.
The output capacitance was adjusted with this smaller foil cap, parallel to the transducer, because it has a larger capacitance than the original.	Small replacement WiMa foil cap on the underside of the PCB, exchanged for a larger cap because the new transducer has more capcitance on it's own.
	New transducer glued to the underside of the vat with JB weld