This is the oldest Beeb I own, an issue 2 with the added bonus of being upgraded to Econet.

There are quite a few differences with the issue 2 Econet interface compared to the later issues 4 and 7.

The first is that all the resistors are mounted standing on end, making them almost impossible to solder to the motherboard.

The second difference is that the issue 2 board provides a facility for the BBC to provide a clock and termination facility.

I think ICs 90 and 92 are the clock generation chips. There are three links related to the clock, S3, S5 and S6. S3 selects the clock frequency, in KHz, in a way I imagine would be similar to the Level 1 Clock. S5 sets or disables the Econet clock. Here the link is set to the south position for Disable. S6 divides the Econet clock by 2 or 4 depending on the setting.

At this time, Econet was very much in its infancy. Clock boxes, terminator boxes and even socket boxes were things of the future. A Beeb at each end of the network would be fitted with the terminator components to the Econet interface whilst a Beeb towards the middle of the network would have the clock generator fitted.

Acorn soon realised that this was impractical and brought out external clock and terminator boxes. This was around October 1982, I think, unless anybody knows any better.

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