The top left-hand corner of the BBC B motherboard contains the Econet interface. In many machines, this is not fitted, with spaces for the ICs and their sockets and resistors to be added.

The issue 4 motherboard saw a major re-design of the Econet circuitry. The clock and termination facility from earlier issues was removed and the layout was changed, in particular allowing the resistors to lie flat against the PCB instead of sticking upwards.

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