[R-390] (I found the problem) NOT!!

[Barry Hauser]

> Alas, life is not so simple.

Somehow I'm not surprised.  That pin terminal may have broken while you were
replacing tubes and was just a coincidence, I guess.
>
> After a smooth replacement of Pin 1 of the 6DC6, (work with the dimple),
and
> reconnection of the leads, the symptoms remain.

Well, at least it's consistent ...

> The symptoms are essentially the same as below, except the putt,
> putt/screeching is more intermittent.  All bands except 3 and below are
> affected.  The putt, putt/screeching is most pronounced with peaking of
the
> antenna trim control.

Which you had replaced altogether earlier ...

>
> A new observation is that with careful peaking of the putt, putt, I can
> almost stop the putt, putt on a PUTT.  At this point, I hear harmonics.
> Tapping anywhere on the chassis will produce stronger harmonics.  Tapping
on
> the 6DC6 will produce very strong harmonics.

It's not out of the question that you have a bad batch of 6DC6's, but more
likely that there's another broken connection.  Systematically tap around
mentally plotting where the harmonic is loudest -- start near the base of
that tube and work outward.  It may get louder somewhere else.
>
> I replaced the 6DC6 with two other tested tubes, with no improvement.

Were they all the same make, same apparent batch?

>
> I will relist the total list of symptoms in a couple of hours.
>
> For now, I am going to test/shotgun all the components associated with the
> 6DC6.  Any other suggestions??

Yes -- more tapology -- tap on the harness components also -- particularly
on the connector shells and cable bundle leading into them where the strain
reliefs typically aren't relieving any strain anymore.  Open up the shell(s)
and check in there.

If you want to escalate the shotgun process -- resolder every connection in
the viciity and in a wider perimeter as well.  There was that thread about
cold solder connections and those that have gone bad.  (There can be a
long-term deterioration/failure mode due to very slow chemical reaction at
the junction of the leads and the solder, sometimes having to do with
residues of rosin and other impurities that failed to boil off during
manufacturing or a repair.)  Bad solder connections -- with a film of some
oxide or other stuff involved -- can form capacitance, or even a diode of
sorts.  (I said "of sorts")

Also, when probing around for connections that really aren't -- gently poke
the leads with small screwdriver to see if anything moves.  If anything
moves -- shoot.  Or, do the shotgun resoldering thing and if it works, it
works -- you just would never know just which one it was.
>
> Hard at work,

If the next stage doesn't do it, we'll have to go for the witchcraft --
either that or I'll hold my breath 'til I turn blue. (Oh well, it used to
work. ;-)

Did you clean the bandswitch, Jim?  Dirty contacts or rotors can cause the
"harmonics" also and that switch is not far away.

Barry