[R-390] Broadcast Band On Other Bands

[Barry Hauser]

Bill wrote:

> For what it is worth, I have the same problem in a Hallicrafters SX-62.
It
> plays beautifully, then gain suddenly cuts down by quite a bit.  If I
switch
> mode to cw and back to am, I can restore normal operation.  I have
recapped
> the receiver and checked all the resistors.  I suspect one (or more) mica
> caps inside one (or more) of the IF cans is opening up.

Possibly a lower-grade problem -- borderline switch contact or bad solder
joint on one of the contacts.  When you switch back and forth, it jostles
the joint just enough to clear it -- theoretically.
>
> Couple of other notes.   The R390 (non-a) here is still overloading on the
> AM broadcast band.  I have recently rocked the bandwidth switch only to
> discover that the center of the bandpass changes when I hit just the right
> spot.  Perhaps the problem is a combination of a recent alignment, and the
> condition of the bandwidth switch.   Further, apparently due to my
> alignment, there are now two peaks in the 16 kHz position.  The switch was
> cleaned, but apparently not well enough.  I have samples of a conductive
> material, will have to try that the next time I can dig into the receiver.

I don't know how advisable it is to use a conductive compound on that
switch.  Try re-cleaning it with DeOxit or similar.  It may take several
go-rounds.  It also may be a weak contact.  There's a way to re-tension
these, but you have to be careful and go slowly.  Use a small piece of paper
or a piece of plastic cut from a blister pack to check for tension of the
contacts against the rotor.  If some are weak, they can open up a smidgen
more when warmed up and break contact.  To add tension back, use a small
allen key or a piece of heavy wire bent at the end to make it easy to slide
it under the loops in the contacts and pull them away slightly.  Then use a
jeweler's screwdriver or some other pointy tool to press on the business end
of the contact.  Takes some dexterity, so...

While your at it, check if the switch is tight to the module and the switch
stack is tight.  Also dress up the solder connections on the contacts as
well as the other end of any short leads connected to them.

> Perhaps this is the solution to the overload problem discussed previously
> (one can always hope).
>
> In the RF section, I now notice some bands will increase in signal
strength
> slightly when the MHz Change switch is rotated slightly.  This is a
> departure from when I first obtained the receiver.  Do R-390's need
periodic
> realignment in the RF section?  The set was pretty gummed up, perhaps it
is
> only now loosening up a little.

Could be the same thing (weak contacts, deteriorated solder joints), or the
mechanical synch is slightly off.  It could be continuing to slip if a clamp
is loose.

Barry