[R-390] R 390A Gear Train

[Dan Merz]

Hi,  my first thought was that either one of the clamps is not tightened
enough,  or one of them may actually be broken and tightening doesn't help
prevent all slippage.  I had a broken clamp on one of my shafts that was
hard to detect visually but defied tightening and I discovered the clamp was
broken on the side away from the screw.  The clamp appeared to be normal to
the eye. And the broken clamp "almost" worked.   I made a replacement that
was designed better than the original,  which to my thinking can be too
easily broken by overtightening.  Not knowing the metal spec on the original
clamps,  it is hard to say what causes this kind of failure,  other than in
my case it appeared that overtightening may have caused it.  In looking
again at my 390,  I wonder however whether your problem may have to do with
the clutch on the zero adjust,  which may not be engaging strongly enough in
the usual tuning condition to transfer one to one to the counter,  i.e. some
small amount of slippage between the two gears involved.  Look down behind
the front panel and see if the two gears involved always move together.
They are coaxial with the zero adjust shaft.  I've never worked on these two
gears so know little about their maintenance but can easily see them
disengaged when the zero adjust knob is tightened and moving together when
the knob is loosened.  Does the frequency tuned always remain the same at
the endpoint?  Or does this frequency also change as the counter changes at
the endpoint.  If the endpoint frequency isn't changing,  then it would seem
your problem is just the counter gear link to the KC tuning shaft and
slippage between the shaft and the counter.  Others may know more about your
symptom.            Dan.  

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of triode45 at aol.com
Sent: Sunday, June 14, 2009 7:51 PM
To: R-390 at mailman.qth.net
Subject: [R-390] R 390A Gear Train

Hello,

I am working on my old Motorola R 390A and decided to rebuild the RF deck. I
followed the directions in the manual and have all of the cams aligned and
have the overshoot of the Veeder root counter at +035.
Everything is now smooth but I have a problem. Let me say that I was able to
tension all of the anti backlash springs properly. 
The problem is if I turn the kilocycle knob quickly to the bottom of the
band and back up, the Veeder root counter will be a little lower, say +034.
If I repeat this a number of times, the counter will continue to drift
lower. I have double checked all of the nonmar clamps and all are reasonably
tight.? Any help will be appreciated..

Thanks,

Alfred
SWL and Ham Band Listener

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