[R-390] 390a - Switch Wafer Alignment

[Dallas Lankford]

Hi Bryce,

I never moved the mounting screws, but I would assume there is enough "play"
to move them sufficiently to realign them.

However, are you sure that is the problem?

Put the MCS knob on its shaft and run the bands from 0 to 30 and back to 0
again as you look very closely at how the nipples make contact with the
wipers.  At various band positions (say 3, and 10, and 17) change back and
forth between adjacent bands while looking very closely at how the nipples
make contact with the wipers.  In oscillator decks that I have examined,
there is quite a bit of backlash... enough so that one wafer is "good" but
the other is "bad."  This is due to the fact that the cutout in the bakelite
disc in the center of the wafer is larger than it should be.  With care and
patience, you can resync the osc shaft (loosening and tightening the non-mar
clamp on the osc shaft gear) so that neither is good or bad, but both are
merely O.K.  As I recall, I adjusted the shaft at least half a dozen times,
maybe several dozen times before I got it like I wanted it.  Anyway, it
fixed my similar osc problem.  It seems like I tried to use thin shims
against the shaft flat through the bakelite disc, but I didn't like the idea
of metal pieces that could fall out and cause other problems.  But that
might be the only solution in some cases

Best regards,

Dallas

----- Original Message -----
From: "Bryce Ringwood" <BRingwoo@csir.co.za>
To: "<R-390" <r-390@mailman.qth.net>
Sent: Friday, April 16, 2004 2:50 AM
Subject: [R-390] 390a - Switch Wafer Alignment


> Hi all,
>
> Pulled the RF section and crystal oscillator last weekend to try and
> cure one or two irritating faults, particularly that of having to rock
> the wavechange switch on the bands 11 to 17 MHz to get reception. On
> close inspection of the switch wafers in the crystal oscillator, I
> noticed that they are out of alignment, with the front wafer being
> displaced sideways just enough to make contact unreliable. The contacts
> on the low range and high range are good. The question is, how easy is
> it to realign the wafer ? It needs to ne moved about 0,5 to 1 mm sidways
> - is there enough play on the mounting screws ? and has anyone else had
> this problem ? Amazingly, the switches and contacts all look bright and
> shiny and new.  Once this is fixed, the only remaining problem will be
> intermittent low sensitivity on the 0,5-8 MHz range which almost always
> presents itself after switching to the 0,5 to 1 MHz range. (Doesn't make
> sense to me, but it might to one of you.)
>
> 73s - Bryce
>
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