[R-390] R-390a Tuning Problem

[fwbray at mminternet.com]

I purchased an R-390a a couple decades ago and replaced the suspect 
capacitors, etc.  I haven't used it a lot in the interim due to high 
urban noise but it has a tuning issue that I never resolved.

Specifically, there appears to be mechanical slippage somewhere in the 
Kilocycle tuning mechanism.  I have made sure that all the cams are in 
the correct position at 7+000 and that the PTO is also correctly 
positioned.  I have also checked to see that there is no excessive play 
in the Oldham coupler.  Everything appears to be tight.

If I turn the Kilocycle knob rapidly, it appears that the PTO gets out 
of synchronization.  I haven't been able to identify any broken or loose 
clamps in the gear train.  I can readjust things so that are again 
aligned but the problem repeats itself.  The gear train is clean and 
lightly lubricated.

Has anyone encountered and resolved this issue.

Thanks.

F.W. Bray