you can test it with a multimeter like this:

In reply to:

Maybe someone else with a multimeter can confirm this.

Pins numbered 16, 19 & 22 of the docking connector should connect to the chassis. Only pin 16 is on mine.

The numbers are printed on the inside of the connector at either end.

they are numbered line this looking from at the back of the empeg:
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17 18 19 20