I have just put my hands on these meters after having them resting on a shelf for 3 or 4 years.
The worked ok, but wanted to calibrate zero by using the popular procedure:
1-power off
2-connect a jumper between zeroing pads
3-power on
4-after some seconds, remove jumper.
Well, I did it on one meter, and got some weird result, so I thought it might be a defective unit. Then I tried the same procedure on another unit.. SAME THING !!!

After removing the jumper, the display won't return to normal operation, but will remain frozen showing -60V and --0A, no matter what input is present. Already tried zeroing again but nothing happens. The meters are basically bricked. Any solution besides firmware update ? I don't have a programmer for these MCUs.