[R-390] R-390/URR - PTO Flatness

[Barry Scott]

I've been working on trying to get the output of the 1st and 2nd
crystal oscillators as well as the PTO up to the level where they
should be.  I replaced R402 and R409 in the 1st crystal oscillator and
R406 and R410 in the 2nd crystal oscillator.  Both of those 150-ohm
resistors were about 40 ohms too high and the other two were at or
slightly over the high side of their tolerance.  After that, I
realigned both oscillators and the voltage at the test points are
within the spec.

Next is the PTO.  As I recall, both R701 and R702 are both high and I
will be replacing those.

What I'm seeing from the PTO's output is that its amplitude isn't
"flat" from end to end.  At TP E210, starting at x.000 on the dial,
the first 400kc or so is relatively flat at approximately -2.7v, but
then it slowly increases to approximately -3.4v and stays about that
level to the top end.

Since the low end of the dial corresponds to the PTO's highest
frequency, then apparently something doesn't like the higher
frequencies.  There are both Xc and Xl in Z702 and I presume it's
designed to be relatively flat across 2.455 MHz to 3.455 MHz but I
don't know if that's the case and something else is affecting this.
Also, I think I've seen at least three different schematics for Z702
and I'm not sure which one is in my radio.

Anyone have any experience measuring this with other R-390/URR (70H-2)
PTOs?  Perhaps this is normal but again, I don't know.

Thanks,
Barry - N4BUQ