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Hi Pete,

the problem is more likely NOT the actual clock circuit itself (found on the
main board using half of IC36 and half of IC28 and sundry other discreet
components). For details of that circuit see section "4" on the main circuit
schematic in the files section.

More likely is that there is a problem with the speed slider pot itself or the
the connector CN2.

The annoying part of this is that the service manual doesn't include an exact
schematic diagram of the speed pot wired into the clock circuit.

So you will need to do some tracing yourself. But I would start by checking that

the slider pot runs through a range of resistance first. You will need a
multimeter for that. If you don't have a multimeter then you will need to find
someone that does or else go buy one.

And then I would check to see that the three wires going from the main board to
the display board via CN2 are not broken. Make sure all thee connections have
continuity.

Mike