[R-390] R390A VFO backlash problem,

[Craig Heaton]

Merry Christmas and a Happy New Year!!

A random thought: I'm not an expert on types of PTO's used in the R-390/A;
but here is what was found in a PTO inside a Motorola.

There is a gizmo sort of like a scissor. A small spring pulls two thingies
in contact with the corrector stack. One of these thingies is the electrical
contact. The other is along for the ride and only rubs the other side of the
stack. If the spring breaks there is mucho slop! Will drive grown men to cry
trying to make all well again!

If this is the cause, the only hope is to open the PTO and inspect the works
inside. My PTO also had the desiccant bag broken with said stuff making the
turning of the PTO shaft gritty. More to the story, but at times this can be
fixed if the corrosion inside hasn't ruined the scissor.

Craig,  

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Roger
Ruszkowski
Sent: Wednesday, December 24, 2014 1:15 PM
To: r-390 at mailman.qth.net
Subject: [R-390] R390A VFO backlash problem,


Fellows,
I was asked this question and I do not know how to cure the back lash
problem in these VFOs. May we have some help please?

Roger, You are going about the end point adjustment the right way. It takes
time and is boring. Tweak it a big bit to get closer faster. You may find
starting from the other end helps you get the adjustment done. 

Hi Roger,
I hope you can shed some light on this PTO problem. I'm asking you because
you seem to have had more experience than anyone else on the 390 list.
I have a Collins type PTO manufactured by Progressitron Corp. for Capehart. 
The PTO seems to have some backlash. If I set it for zero beat, it will jump
back about 300Hz when I let go of the knob or shaft (with PTO removed). I
have cleaned and lubricated the leadscrew and put a drop of oil in the front
bearing, but it still does this. Any suggestions??
I have the PTO on the bench, coupled to a counter. The freq. was off quite a
bit (~2kHz) after 10 turns. I have adjusted the endpoint slug and now have
it within 700Hz. I have a pointer knob on the shaft, and have been setting
the PTO at 3455.0 and marking the front plate, then after exactly 10 turns
(2455.?) I see where I am relative to the starting mark and make another
tweek of the slug. Back to 3455.0, another mark and do it all over again. Is
there an easier way to make this adjustment?? I'd like to get it closer, but
all this back and forth is driving me to drink!!
Looking forward to your comments and suggestions.
Roger Gates, W7KVT 

Thank you Fellows,
Merry Christmas to all

Roger Ruszkowski  AI4NI
 
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