The Layout of the mainboard varied throughout the revisions, here is an example:
Examples of different mainboards are here:
This one is missing the 5 and 12v connectors as well as the RM Cartridge connectors
This board has a 9 Pin D socket for the network, rather as onboard as above.
This board looks to have the component spaces for the network but they were not fitted.
Perhaps for cost cutting or maybe aimed at the home market.
It also includes ROM cartridge slot connectors (the blue blocks on the left)
This is is the 'facelift' slimline pc-186 mainboard, please see this section for more information.
Many differences here, notably the different RAM chips(bottom left), also
the different angled add-on memory card socket (bottom left) and extra power connectors (bottom middle)
The notable difference on this board is that there is no soldered onboard memory, just empty sockets (bottom left)
No high resolution image for this one.
Other Examples of the original Nimbus PC are as follows: