[R-390] VFO endpoint adjustment - stumped!

[Joe Foley]

Tim,

If you're sure the stoppage is inside the PTO then the
best course of action is to open it up, no amount of
guessing is going to verify what the problem is.

You might check the run-out of the shaft just to see
if there is anything to see.  It may show a bend that
will let you know what to expect when you get inside,
maybe.

Someone mentioned in the past needing to leave the
rear mount loose to accomodate movement in the shaft
due to being slightly bent.

Joe

--- Tim Shoppa <shoppa_r390a at trailing-edge.com> wrote:

> OK, I'm stumped.
> 
> I'm putting my yellow striper back together. Right
> now the VFO covers
> a range of 2.500MHz to 3.6MHz. At the low end it
> hits some sort of
> apparent mechanical stop. Didn't hit anything at the
> high end because
> I don't need to turn it that far :-). It is supposed
> to cover 2.455
> to 3.455 MHz (and with 25kHz of under-run it ought
> to go to 2.430 MHz)
> just as a reminder.
> 
> Even though it doesn't span the right range, the
> linearity is pretty
> good, and in the first ten turns it is always within
> 0.5kHz of being
> on the money.
> 
> I look in the Y2K manual, but the endpoint
> adjustment screw illustrated
> there does not match my unit physically. There is a
> plug-screw in mine,
> but it's on the left hand side, outside the triangle
> frame as seen from
> the front. The one in the Y2K manual is shown as
> being inside the
> triangle frame and a bit on the other side.
> 
> Inside the plug-screw, I find some sort of slug that
> can be turned
> with a 3/8" screwdriver bit. The slug seems to be
> hollow and probably
> brass. Turning it does nothing, doesn't budge the
> frequency at all.
> 
> There is another access hole, inside the triangle
> frame, that has a bunch
> of little set screws in it that slowly scroll past
> as I turn the dial.
> I think these are obviously the linearization
> screws. I do not want to
> screw up the linearization of this PTO, I am very
> happy with it as is.
> 
> Oh, and I pulled the metal rectangular cover from
> the box, and found
> some resistors.  Hmm, that 2.2k resistor looks a
> little suspiciously
> brown, better check it out.... actually 8K!!! This
> makes the score on
> this radio for a total of seven 2.2K resistors that
> were too high
> in value by hundreds of percent! (Almost all of them
> in the plate lines).
> So I fixed that.
> 
> So how do I adjust the endpoint on this PTO? No
> maker's label on the outside,
> but there is a refurb sticker from Raytheon,
> indicating a service date
> of Feb 7, 1976. At one point I brought it up and I
> think the suggestion
> was that it was a Motorola? I could be recalling
> that incorrectly.
> 
> Tim KA0BTD
>
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