[R-390] RF deck questions

[Barry Hauser]

Hi Andy & list:

> I finally had time to start work on the R-390 I bought last year.
> Last weekend, I discovered that the RF deck will not mechanically
> tune past the 25 MC band. Since this unit has had some bad repairs
> done in the past, I was wondering if this could be the result of
> installing the RF deck without the green gear? Or is this likely to
> be a mechanical failure?

The thing to do is a full mechanical alignment/synchronization which is
spelled out in the manual.  (Or at least walk through it.) The green gear,
when used properly, avoids the need for this when the RF deck is removed for
service or swapping between radios.  It could have been that, or some clamp
came loose and was tightened with things in the wrong position.  May just be
that the MC section is not synched right with the 10-turn stop.
>
> Which brings up another question: What do I use to clean and
> lubricate the gear train? Will SuperTech General Purpose Lithium
> grease work?

Are you kidding?  There are those on the list who would shudder at the
thought of another lube thread.  Just in case you're serious, a good grade
of motor oil, particularly Mobil One, is popular.  Don't use lithium grease.
After cleaning the gears, cams, cam followers (make sure they turn freely),
etc. apply very little oil to the gear teeth with an artists brush.  Use a
bent paper clip to apply a drop to each bearing.  Wipe away any excess.  One
quart of Mobil One will be sufficient for 500-1000 radios, or one R-390
until the year 12002.  This mostly benefits future owners as it shouldn't
solidify and gunk up the works.  Shows concern and compassion for
generations to come so the archeologists of the future will look favorably
on our culture and not write us off as a bunch of glorphomorphs.  ("Hmmm ..
they had the technological prowess to design such a thing, but look how they
lubricated it.  I give 21st century man a C minus.")
>
> So far I replaced 1 tube socket in the power supply, the 4 47 ohm
> resistors in the power supply and half the power supply wiring
> harness. In the audio module I replaced C607 as a precaution, the 4
> 47 ohm resistors, fixed several bad solder connections and replaced
> some of the wires. The B+ regulates at 190v after replacing R626.

Sounds like your B+ is running high.  As part of an analysis about a year
ago, I polled some R-390/391 owners on the list asking them to check the B+
while varing AC supply voltage from 95 to 125 with a variac.  As I recall,
the B+ held to within +/- one or two volts from 180.  For some reason, one
Motorola was virtually dead on over that range, out-performing the Collins
units.  So, even if your line voltage runs high, the B+ should be in
range -- maybe 182 tops.

Barry