[R-390] kilocycle/megacycle movement

Mon, 30 Dec 2002 19:45:39 -0600

I'll hazard a guess here that after a thorough disassembly, cleaning and
degreasing of the gear train, most of us very carefully put that good 'ol
slippery Mobil 1 30W on everthing in sight. Some of that oil will inevitably
find its way onto the shafts during reassembly, just from oily fingertips if
nothing else. Then we clamp down on a nicely but inadvertently oiled shaft
with the old Bristol wrench instead of on a completely dry shaft, and voila!
slipping clamp one of these days... Don't know how one can prevent this,
unless a final degreasing of the shaft and inside of the clamp with Q-tips
prior to putting on and tightening the clamps might help. It might even
allow nice tight clamping without so much pressure on that poor wimpy little
screw.
73, Jerry W5KP

----- Original Message -----
From: "Dan Merz" <[email protected]>
To: "Jim Miller" <[email protected]>
Cc: "R-390 List" <[email protected]>
Sent: Monday, December 30, 2002 6:05 PM
Subject: Re: [R-390] kilocycle/megacycle movement

> Hi all/Jim,  I took a look inside and did some reach-in
cleaning/inspection but
> didn't find anything obvious.  And the detent spring seems to be ok though
> difficult to inspect.  I can't see all the cam alignment marks but noticed
the
> 4-8 mhz cam was off the mark some but was still operating on the right
> surfaces.  The 2-4 mhz cam mark is not too visible but I noted that it
didn't
> look right as far as how the cores were traveling at the upper end of 3 to
4
> Mhz -  aha ,  the  Mc/Kc link that started the Mc knob moving occurred
when
> near the upper end of the range around 3.92 Mhz where the core rider was
> actually dropping on the wrong side of the cam surface.  The cam is out of
> proper adjustment,  and the cam surface is steep enough on the "forbidden"
side
> that it locks the cam shaft which forces the detent on the Mc  knob to
give way
> to accomodate the motion of the Kc knob as I tune within the band.  Mind
you,
> this doesn't take much force on the Kc knob,  hardly different than
regular
> tuning so there must be some gearing that is helping the detent
disengagement -
> I didn't quite have the patience to analyze that .   Intuitively,  I would
have
> thought it would be the other way around - a lot of force on the cam to
hold it
> solidly enough to disengage the detent.
>
> I haven't figured out where the loose connection is that got the 2-4 cam
out of
> sync,   I guess the gear on the cam shaft since that's closest.  I seem to
> remember checking these alignments when I first got the radio a couple of
years
> ago and I haven't loosened anything in the gear train except to put the
pto
> oldham coupler  in the right position after I worked on the pto.  I think
> pulling the front panel is probably the best step to take next so I can
see all
> the cam markings and alignment.  Or is there an easier way?  thanks for
all the
> suggestions,  some of the split gears were checked and seemed ok.  So far
I
> haven't seen a shaft slipping in a gear but that could be happening.
>
> Dan
>
> Jim Miller wrote:
>
> > Sometimes a coil slug will stick at a band edge causing low sensitivity.
> > Look at the slug rack as you tune at the high end and see if any slugs
stop
> > moving prematurely.  If you see one, tap on it ot wiggle it by hand to
see
> > if sensitivity returns.  If it is a slug that is sticking, you can
usually
> > free it up by loosening the screws that hold it to the slug rack and
allow
> > it to re-seat itself so it doesn't bind.
> >
> > Dan Merz wrote:
> >
> > > Hi,  I haven't used my  390a much over the last 2 or 3 months and I
was
> > > listening on 80 meters tonight and found a problem tuning up near 4
> > > Mhz.  It seemed dead there and I could tune in stations down near 3.9
> > > somewhat better (I started listening on another set for comparison to
be
> > > sure the band wasn't dead).  After awhile I noticed that the megacycle
> > > knob seemed to move off its "lock" position and was moving as I tuned
> > > the kilocycle knob.  It did this sometimes and would get off the band
> > > position but not always.  Is this most likely a lubrication problem?
I
> > > really never was able to pick up a known signal at around 3.99 Mhz and
> > > I  tried rocking the megacycle knob to improve things,  or to find if
> > > something else was "hanging up".  I haven't lubed the set since about
2
> > > years ago when I did a pretty thorough job in this regard and
everything
> > > seemed very free.  I'll pull it open tomorrow and take a look but was
> > > curious if there was an obvious known component that causes this kind
of
> > > symptom. It seemed ok on other bands but I didn't spend a lot of time
> > > checking.   thanks,  Dan.
> > >
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