[R-390] Trouble Shooting R390A/Backlash

[Tim Shoppa]

>  The lower and upper frequency ends seems to move about 1 to 2
> clicks while the mid freq range, approx 300 to 500 appears to move
> as much as 4 clicks. Can anyone point me in the right direction as
> far as adjustment(s) to correct this? Hopefully nothing is warped. 

Check the Oldham coupler (between the kc knob and the PTO)
and the split gear that drives the counter for missing springs.  From
the bottom you can see where the springs are supposed to go.

If the gears are rusted or burred then it may not matter if they've
got the springs or not.  Without taking apart the geartrain you
ought to be able to wiggle the two halves of a split gear just
a tiny fraction of a tooth and feel/see them snap back.

If turning the kc knob causes neither a change in frequency or
movement of the counter, then it's likely the Oldham coupler
spring.  If turning the kc knob does cause a change in frequency
but doesn't cause the counter to turn, then it's likely the gears
that drive the counter.

Also the two bevel gears that do the right-angle thing to drive
the counter may be not close enough, that would cause some
counter backlash too.

Not sure exactly why the backlash would depend on position of the
kc dial.  The springs pulling down the cams do exert some
torque backwards through the geartrain.

Oh, wait, if one of the two springs on a split gear was missing,
then you might see the effect you see, although it would depend
not on kc display but on the angular position of the kc knob.

Tim.