[R-390] First 390A Alignment prep and weak bands

[Dennis Wade]

Thanks Tim for the reply.

I completed the first pass on the alignment tonight with generally
good results.  A couple things of note for the list:

    Stagger tuned the fixed 455 if, and to my surprise, both top and
bottom cores of T-503 were fairly far off peak.  Didn't expect to see
such big gains from a stage I didn't go anything to.  Seems to operate
normally though.  Crystal deck trimmers were generally right on peak,
but couldn't hear the peaks on 2-3 and 3-4.  Used the upper bands for
that adjustment.  Both variable IFs peaked nicely with some increase
in gain.

    2-3 and 3-4 mc/s are deaf as stumps.  In particular, the core for
L-217 is all the way at the bottom of its travel with no real peak. 
Mechanical alignment is fine.

     Haven't set the IF gain pot yet, that will be the last thing I
do.  I want to find the trouble with the 2-4 mc/s section first.

          Looks like I need to pull T-203 again and have a look at the
innards.  Any idea what I should be looking for?

          Thanks...Dennis

On 7/31/05, Tim Shoppa <shoppa_r390a at trailing-edge.com> wrote:
> > The signal level was fairly consistent across all bands with the
> > 2 and 3 mc/s bands being the notable exceptions.
> 
> With regards to RF alignment, the bands are:
> 
> 0.5-1 MC
> 1-2 MC
> 2-4 MC
> 4-8 MC
> 8-16 MC
> 16-32 MC
> 
> It looks like you need to check out the 2-4 MC RF section.  Not just
> alignment but condition of the coils/caps, bandswitches, etc.
> 
> Sometimes the variable caps go shorted, other times the inductors
> go open-circuit, etc.  The latter especially when somebody pumps a
> few hundred watts of RF into the front end!
> 
> Sounds like your variable IF sections are OK too.  Not that they can't
> be topped off, but look where the problem is first.  Tuning up your
> IF's won't make 2 and 3 MC come back.  The right time to do the alignment
> is after you've gotten all the bands working - if you have to change out
> some parts then you may subtly affect the alignment of other bands.
> 
> It's vaguely possible that the crystal oscillator section for 2 and 3
> MC's are both out of kilter but it seems unlikely.
> 
> And check mechanical cam alignment before suspecting any of the
> electronics I mention earlier!  Sometimes it's as simple as the clamp
> for the cam in question being loose or the springs not working for that
> band.
> 
> Tim.
> 


-- 
Dennis L. Wade
KG6ZI
Carmichael, CA