We will be continuing maintenance on the wiki starting this Saturday at 9 am (UTC) to Sunday at 7PM (UTC).

There is a possibility of long maintenance-breaks and downtime during this time.

For more information contact us in the wiki Discord or by email at: unto@fighttorepair.org

Grundig UC6620

From Repair Wiki
Jump to navigation Jump to search

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
fractured broken piezo ceramic disk
The destroyed transducer after removal
Open circuit resistor coupling the rectified voltage to the driver
Resistor burnt on the underside, with damage not visible when installed.
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.

UC6620 main PCB with the broken 0.1 ohm resistor replaced with 10 parallel 1ohm ones.
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.

smaller foil capacitor, put in place for a larger cap because the new transducer has more capcitance on it's own.
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
New transducer glued to the underside of the vat with JB weld