[R-390] kilocycle/megacycle movement

[Dan Merz]

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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