[R-390] Advice Please

[Mack McCormick]

I have a R-390 (non-A) and a R-391. Both work great but the R-391 cannot be
 adjusted using the zero adjust on 3885 Kc. It is 3 Kc high (3888 Kc). It
can be zero adjusted at 10 MHz.

The R-390 can be zero adjusted perfectly on both frequencies. Since the
R-390 is accurate I removed the 1st and 2nd oscillator module and placed it
in the R-391. It still will not adjust on 3885 KC (Still 3 Kc high). So
that really only leaves the PTO in the frequency accuracy chain.

Do you recommend loosening the set clamp on the R-391 PTO and tweaking it
slightly as recommended in the manual? Is there something else I should
investigate and try?

Thanks in advance for any ideas. I’ve rebuilt over a dozen R-390A’s and I’m
very familiar with them but new to the non-A series.

73,

Mack
W4AX
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73,

Mack
W4AX
https://www.qrz.com/db/W4AX