The galvos need to be operated in differential mode. This is determined by jumper  settings on the galvo drivers boards. They are usually shipped configured for ‘common mode, non-inverting’ To switch to differential mode, only jumper 1-3 need to be connected. This usually means that jumper 4-6 needs to be disconnected. (see MicroMax Series 671 Cambridge Technology manual). 

Make sure the driver power is turned off when plugging in the galvos.

Zero the inputs through the BNC cables

The LEDs on each driver board should turn green after the power is turned on.

The driver boards are arranged in the order 

X , Y1, Y2  

Y1 is the first mirror in the path. 

Y1 is spec'd for M30 (30 degrees peak to peak)

An offset is applied to Y1. This offset is tweaked using the front panel 10 turn pot.

Y2 is spec'd for M40