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

[Dr. Gerald N. Johnson]

On Mon, 2007-11-19 at 23:40 -0800, Chris Kepus wrote:
> All,
> 
> This may be a bit long but I would really appreciate a response if you have
> taken a Cosmos PTO apart.  I haven't taken one apart...yet.
> 
> I just picked up a Cosmos PTO for my R-390A. I liked the fact that Cosmos
> came up with a design that didn't require messing with a corrector stack.
> Others have pointed out that repairing and calibrating the Cosmos isn't for
> the faint of heart, but it can be done. (I know, fools rush in..) 
> 
> 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.  The fragile elements on top of the output transformer were in
> good shape with no observable damage... Anyway, in addition to scratches, it
> was evident that someone had pulled the outer cover since only one of the
> screws had the accompanying lock washer.  And the heater was possibly
> removed because the screws that retain the heater (and insulation) were
> missing.  If it is possible to remove the heater without unsoldering any of
> the leads, it might have been removed. The heater wires did not look as they
> had been unsoldered (could they have been cut at the top? ) My leads have
> what appears to be shrink wrap over about an inch of them where they go
> across the rear of the heater "can" assembly.  Photos at
> http://www.flickr.com/photos/w7jpg/.
> 
>  Lastly, how should the PTO shaft feel when rotated by finger power?  I
> expected low resistance and a smooth feeling rotation.  Mine is rather stiff
> and when rotated, has an odd feeling, similar to rotating a shaft with
> "soft" detents...not smooth at all.
>   
> So what do you think?  According to the writing on R390.com and elsewhere by
> authors like John Harvie, Dallas Lankford, and Tom Marcotte, there doesn't
> seem to be many conditions that cannot be repaired.  Is there anything I
> mentioned that causes you experienced folks to be concerned (other than my
> inexperience?)  Is there anything else that I should be looking for before
> diving in? 
> 
> Thanks es 73,
> Chris
> W7JPG
>  
> 
Stiff and lumpy shaft rotation is a symptom of the lubrication having
dried into lumps. Some disassembly is required to clean and relubricate.

As I recall, the Cosmos PTO replaces the washer stack that takes much
skill to adjust for linearity with a gang of screws through an internal
rotating plate.

In my collection I have a web page titled "
                 A JOURNEY THROUGH THE COSMOS (PTO)" by

                    Jim Miller N4BE, jmiller at iu.net

that has 8 or so close up pictures of the mechanics of the Cosmos PTO.
Its on line at: http://www.r-390.com/cosmos.htm Googling "cosmos pto"
turned up 106 hits some with many details like this one. Well the first page 
said 106, but it showed only 30.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer