[majoconz]

Two things have shown themselves - the boards behind the frequency display are a frequency counter which I can make to count -25Hz right up to 1.3GHz. Immediately behind that is an input attenuator which should be fed fro the buttons on the front panel but I actually suspect those buttons control the logarithmic attenuator. Behind that on top which had me baffled until I found a circuit diagram that matched the components and so I deduced it was a sawtooth generator. There's three potentiometers on there - the diagram says they are sweep width, amplitude and linearity. Twiddling one at a time (so that I could return them to their original position) affects the frequency display - but now I need to find the oscillator that it's sweeping. There's a 555 timer on that board which probably resets the sweep rate so I'm hoping if I stop the timer I might get one fixed frequency, I suspect at the start or the end of a sweep. We'll see!