[R-390] Question on COSMOS PTO

[Jon]

Hello to the Group,

I'm continuing my saga of just zero beating against the calibrator mark and
have notice the following observations which I think are cause to be
concerned.

1. Zero beating against the calibration 100Khz signal at x.000 after using
the zero adjust knob to be exactly at x.000, I noticed that if I either dial
up or down from this calibration spot, coming back to this mark, I'm always
either +/-100Hz off depending on the direction I'm turning. Is this what you
call backlash or hysterisis?

2. Doing the same experiment as described above only this time using a
counter and taking note of the frequency, I observed that starting again at
3.455000Mhz with the dial set to x.000 and dialing up or down the frequency
can be off as much as 80Hz i.e. 3.45508 in returning again to x.000. I also
noticed that by pressing on the KHz knob with just pressure from my hand I
can cause the frequency to be off again as much as 80Hz. And since the 390a
is on its back I can touch the PTO and cause 10s of Hz of be off.

This is my 1st 390a and I don't have any experience in the feel for
calibration. Am I approaching the design limit being off +/- 100Hz on the
calibration mark? It seems to me something is either up with the PTO or the
mechanical linkage to the PTO. The oldham coupler is aligned as best I can
with a new backlash spring and I'm also keeping to the .032 spacing as best
I can. The ground strap is present and looks good against the shaft. I'm
really kinda of frustrated at this point and any help would greatly be
appreciated.

Thanks in advance,
Jon,KB1DC