[R-390] Removing Megacycle Change shaft

[Jacques Fortin]

Just curious, Paul:

What is the maker and serial # of this R-390A ?

 

73, Jacques, VE2JFE in Montreal

 

De : Paul Roche <rochep at comcast.net> 
Envoyé : 15 juin 2026 23:17
À : Barry Scott <72volkswagon at gmail.com>
Cc : Jacques Fortin <jacques.f at videotron.ca>; r-390 at mailman.qth.net
Objet : Re: [R-390] Removing Megacycle Change shaft

 

Thanks all. This is a lot to digest for someone who came across an R390A for the first time yesterday. I will study up on the terms you sent and get back to you. A 2 piece would be easiest, now how to “destroy” the rest of the broken clamp. Dremel would leave lots of metal debris. 

 

As yes there is a hole 180 from the “pin” but no hole in the shaft so I can’t get to it. This will sit for a while; lots for a newbie to think about. But it sounds like this “travel stop mechanism” is not to be messed with (by me). 

Sent from my iPhone





On Jun 15, 2026, at 11:05 PM, Barry Scott <72volkswagon at gmail.com <mailto:72volkswagon at gmail.com> > wrote:



Thanks, Jacques, for that clarification.  Mention of an Oldham coupler threw me just a bit and I wasn't seeing the heart of the problem.  Fortunately, I've never had to deal with a broken clamp there.

 

A two-piece clamp would work nicely there because, if I'm thinking correctly, once it's in place and tightened, it isn't necessary to loosen and adjust it like some of the other clamps might need.

 

Thanks,

Barry - N4BUQ

 

 

On Mon, Jun 15, 2026 at 9:30 PM Jacques Fortin via R-390 <r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net> > wrote:

Hi Paul,
That circular "ring" is a part of the travel stop mechanism and is actually
pinned to the shaft.
Reference to your sent picture, if you turn the MC shaft 180 deg. did you
see a hole on the other side ?
If yes, you have to use a 3/32" drift pin thru that hole to push the lock
pin out.
Be careful, as you will have to re-install it (and all the travel stop
disks) when you will re-assemble it.
And this is not the only difficulty: there is also a circlip locking the
shaft on the other side, plus a lot of shims.

IMHO, you will have to remove the whole RF deck from the set to be able to
work properly on that problem.
Another way is a disassembly + reassembly of the front plate.

Last idea: if you can remove the remnants of the broken clamp, you can
machine a 2-part clamp that use 2 screws to jam the gear to the shaft.
Advantage: no lock pin to remove (will be a PITA, guess how I know) and no
front mechanism plate removal and reassembly.

Some other people on this forum can have different opinions, if so, go on !

See the attached pictures (from my "spare" R-390A RF deck).

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <mailto:r-390-bounces at mailman.qth.net>  <r-390-bounces at mailman.qth.net <mailto:r-390-bounces at mailman.qth.net> > De la
part de PAUL ROCHE via R-390 Envoyé : 15 juin 2026 20:24 À :
r-390 at mailman.qth.net <mailto:r-390 at mailman.qth.net>  Objet : [R-390] Removing Megacycle Change shaft

Just got my first R-390A and the Megacycle Change shaft just spins and
spins; the Oldham coupling clamp is broken. But the problem is to remove the
shaft I need to remove the circular "ring" attached to it. I am looking for
a setscrew, but this doesn't look like any setscrew I have ever seen! I
might have to drill it out unless someone has a better idea; what is this
thing and how to i get this circular ring loose so I can pull the shaft to
add a new clamp?

Paul
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