The hardware changes:
The supply, the first letter (Xxx):
S = Standard 6-pulse with chokes
B = 6-pulse with choke and DC connection
N = 6-pulse, no chokes for spare units
T = 12-pulse
U = 12-pulse, no chokes for spare units
H = 6-pulse, no AC chokes, and with DC connection for spare units
The mounting, the second letter: (xXx):
S = Air-cooled drive
O = DC fan external supply
The boards, the third letter (xxX):
F = Direct connection/non varnished
G = Direct connection/varnished
A = Fiber,integrated control
B = Fiber,integrated control, Varnished
N = IP54 control unit for standard/fiber connection
O = IP54 control unit for varnished/fiber connection
X = IP00 for cabinet use, standard PCB
Y = IP00 for cabinet use, standard PCB, varnished