[R-390] Cosmos PTO for 390A - newbie - Help requested

[Chris Kepus]

All,

This is a bit long but I would really appreciate your taking a look.  I have
to operate on a PTO, I believe, and this is the first one I've put a hand
on.....yep....I haven't taken one apart...yet.

I just picked up a Cosmos PTO that is intended as a spare for my R-390A. I
have a Collins built R-390A but I am unwilling to pull anything out of it at
this time.  It is working quite well.  I got the Cosmos because I like the
fact that Cosmos came up with a PTO design that didn't require tinkering
with a corrector stack in order to adjust linearity.  Others have pointed
out that repairing and calibrating the Cosmos (or any PTO) isn't for the
faint of heart, but it can be done. (I know, fools rush in..) And, as I have
read in the archives about the repairs that have been done by you all, you
"git it done"! 

Back to my Cosmos.  Although the seller said it was dusty (it is), he didn't
say the outer cover of the PTO had numerous scratches suggesting a rather
"rough" storage environment.  Nonetheless, the fragile elements on top of
the output transformer are in good shape with no observable damage... It is
also evident that someone had pulled the external cover since only one of
the screws had the accompanying lock washer.  And the heater and/or
thermostat was possibly removed.  The screws that retain the inner cover are
missing.  Is it possible to remove the heater without unsoldering any of the
leads? The 11-856A Tech Manual talks about unsoldering the thermostat leads
when replacing it but nothing else except a warning about not removing the
inner cover. The heater or ther mostat wires did not look as they had been
unsoldered although under a magnifying glass, it is possible a resoldering
job was done that was equal to the original  One of my heater leads crosses
behind the inner cover and has what appears to be shrink wrap over about an
inch where it is routed across the rear of the inner cover assembly (could
they have been cut at the top?).  I have posted a number of photos at
http://www.flickr.com/photos/w7jpg/.  When you click on a photo, it gets
larger.  Just above the picture on the top left side is a small "All Sizes"
and magnifying glass icon.  Click on that for yet another enlargement.

How should the PTO shaft feel when rotated by finger power?  I expected low
resistance and a smooth feeling rotation.  Mine is quite stiff and when
rotated, has an odd feeling, similar to rotating a shaft with "soft"
detents...kinda lumpy and not smooth at all.

Is there a manual that shows how to disassemble the PTO (and other modules)
in detail?  My 11-856A Tech Manual doesn't except.  Can someone tell me
what's necessary to remove the heater and insulation?  It sounds like the
thermostat leads may have to be unsoldered but I hate to unsolder something
if it's not necessary.  Once past that, I can pull the inner cover and take
photos of the innards. And, Miller's article on "A JOURNEY THROUGH THE
COSMOS (PTO)" should be very helpful.  Hopefully, I won't find an exploded
dessicant pack or rusted out assemblies. 
 
I am encouraged by the writing on this list and the articles on R390.com and
elsewhere by authors like John Harvie, J Miller Dallas Lankford, and Tom
Marcotte.  There doesn't seem to be many conditions that cannot be repaired.


Is there anything I mentioned or that you see in the photos that causes you
experienced folks to be concerned to the point that I should perhaps have a
discussion with the seller before proceeding further?  The PTO was described
as "pulled from a working unit" by the seller (no, it's not Martyn! <g>) in
response to my question about where it came from.  Otherwise, it's time for
me to get my feet wet.  

Thanks, Happy Thanksgiving and 73,
Chris
W7JPG