[R-390] Collins R 389 PTO

[2002tii]

Roy wrote:

>Here are just a few of the things wrong with the PTO in my R-389:
>
>- The coil form is cracked loose from the mounting plate, cracked 
>clear through part way through the windings and twisted out of position
>- The core is cracked and there are small pieces missing
>- The corrector stack follower mechanism is bent 90 degrees from normal
>- The corrector follower mechanism is torn loose from the tuning rod assembly
>- The corrector stack mounting frame is bent
>- The tuning rod is bent.

I have had decent results repairing broken ferrite cores -- including 
R-389 PTO cores -- with thinned epoxy (I use acetone to thin the 
epoxy I use; other epoxies may prefer toluene, xylene, isopropanol, 
methanol, or ethanol -- test before doing it for real).  Others swear 
by cyanoacrylates.  The more voids there are due to lost ferrite 
crumbs, the less successful the procedure.  Internal voids are more 
serious than end chips.  Sometimes I grind ferrite from a sacrificial 
core until it is a very fine powder, mix a pretty dry putty with 
thinned epoxy, and use it to fill the gaps (this works best when the 
powder is the same grade of ferrite as the core, but it can work OK 
even when it's not).

It's a lot of work, and VERY messy -- but for truly irreplaceable 
cores it can be worth it.

The coil form just needs to be properly jigged and then 
epoxied.  Tedious, but not difficult.  Make sure you preserve 
clearance for the core.  And be sure to use enough release agent on 
your jig components!

I'd be inclined to fabricate a new tuning rod and follower, but if 
you don't have the appropriate machine tools you can probably fix 
what you have.  Hopefully, the mounting frame can be straightened 
with a hammer or a vise and appropriate dollies or blocks.

Everything can be fixed -- it's just a matter of how much effort you 
think is worth spending.  Since the PTO is almost always the thing 
that's broken in 389s, there aren't many spare PTOs available.  And 
when they are, the owner knows what they're worth.

Finally, fix the PTO clutch and unsolder the motor leads!

Best regards,

Don