In order to reset the fusing unit for Konica Minolta 420, follow the steps.
Step 1. Press these keys:
zahler > detail > stop > 00 > stop > 01.
If nothing appears after having pressed these keys, try this.
Shut down the machine, power it on, keep “zahler” pressed and when you see “Trouble Reset” appearing on the display, press the following keys: stop > 00 > stop > 01.
You will enter into Initialisation tab > Counter data > Fuser tab and press “start”.
The same method works also for replacing the cilinder. You will need to reset all the counters.