[R-390] kilocycle/megacycle movement

Mon, 30 Dec 2002 15:06:58 -0500

I don't know about the split gears either -- not good if they're stuck, but
probably not the cause of Dan Merz's problem.

A bit more about the slipping clamp deal -- The works can appear to rotate
OK though part or most of its travel, until a certain point in the upswing
of the slug racks, where the spring tension is at it's highest.  Then a
shaft can slip for, say 1/8 turn.  Rotating in the reverse, it slips again
over that range and then grabs as the remaining friction is then sufficient
when the slug rack springs are relaxed.  That clutching action can be very
consistent.  It can cause the radio to mistune or go dead through part of
the band.

It's difficult to spot.  You have to force yourself to look at each
shaft/gear set and watch to see if the gear stalls as the shaft continues to
rotate or vica versa -- through the full range of the band(s).

Another more basic possibility is that the mechanical synch is slightly out
somewhere.  And, yeah, I suppose there are other possibilities, like a
hanging slugrack -- on the downswing.  That will also be very consistent.
Looks like the little roller bearing is following the cam (they're cam
followers, aren't they?), but then the slug hangs and the bearing is really
suspended a fraction of an inch over the cam, not resting on it.  Might be
flush in front and high in the back.  As a slug rack moves down to its
lowest position, gently tap on front and back to make sure it's really all
the way down against the cam.

Gotta look at the thing ... in motion.

Barry

----- Original Message -----
From: "Scott, Barry (Clyde B)" <[email protected]>
To: <[email protected]>
Sent: Monday, December 30, 2002 12:48 PM
Subject: RE: [R-390] kilocycle/megacycle movement

> While this indeed could be a problem, can the symptoms described be caused
by backlash?  If tuning up from 3.8 to 4.0 and the radio becomes "deader"
towards 4.0, the backlash would all be in the same direction.  I'm not sure
how this could be the problem here.
>
> Barry - N4BUQ
>
>
> >
> > Don't forget the possibility of the split gears having
> > burrs on them and being stuck together so that they
> > can't take up the backlash.  They should be taken
> > apart and honed flat.  Especially that little one on
> > the right hand side that has the spring inside the two
> > halves.  Mine was stuck TIGHTLY together.
> >
> > Nolan would have raised this point.
> >
> > Joe
> >
> >
> >
> >
> > --- Barry Hauser <[email protected]> wrote:
> > > Hi Dan & Gang:
> > >
> > > In addition to a worn, bent or loose detent
> > > spring/plate, check carefully
> > > for a loose or broken gear clamp.  A broken clamp,
> > > or one that isn't
> > > positioned right, may snug up with the bristol
> > > wrench, giving the false
> > > impression that it's tight.
> > >
> > > The situation sounds familiar.  I got one unit in
> > > here a few months ago and
> > > noticed the MC knob creeping.  One broken and one
> > > loose clamp.  I don't
> > > recall which ones.  You have to look carefully
> > > behind the panel as you
> > > rotate the KC knob with the MC set in various
> > > positions, including the 4 MC
> > > position.  The mechanics of the gearworks is such
> > > that the backlash varies
> > > over its travel, largely due to the spring tension
> > > on the slug racks..
> > >
> > > As suggested, gunked up gears could do this, but
> > > they'd have to be pretty
> > > bad.  Check all clamps using the close eyeball
> > > inspection method.  And,
> > > whatever you do, don't blink!
> > >
> > > Barry
> > >
> > >
> > >
> > >
> > >
> > > Dan 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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