what can anyone tell us about this board?

[Paul Berger (Canada)]

That board looks like it would completely replace the electronics board in a 48 so my guess would be either it was used to integrate a 48 style keyboard into another device or was used in development of the the second generation 48S machines that used a Yorke processor or the 48G series. By the time those calculators where in development they would have already had the the keyboard for the earlier 48S and with this board they could conveniently hook the keyboard to development hardware that they could have out in the open for instrumenting, and also for code development could include an EPROM for easy update which would not fit the finished machine.