[Misc] 1 out of three 1200ps printing the wrong shade of grey

[AB1984]

In the artwork its showing up as 20% black, and it came up fine on the first two printers. The third though prints it really pale, even though the pure black bold text above the light grey box is no different. I've had a go changing the maximum density in manual adjust. I've tried dipswitches 5, 15 and 27 and the appropriates bytes, still nothing...
Any ideas?