[R-390] TR: RF Deck Removal and Questions

[Jacques Fortin]

Hi Alex,
To your questions:
1_ Replace C231 which is a 50µF, 50V electrolytic in a "bathtub" case mounted inside the RF deck chassis. This capacitor is most probably not good anymore.
2_ Position of the MC and KC before removing and before re-installation at "00-972" VS setting to check the cams at "02 000" on the counter:
See TM11-856 pages 115 and 116, with page 116 corrected per Change # C-4.

73, Jacques, VE2JFE in Montreal

Jacques, Barry - thank you for the help!
Last night I was successfully able to extract the RF subchassis, appears to also be a Motorola.  Now begins the process of cleaning and lubricating.
A few questions:
While the RF subchassis is out on the bench, what components underneath should I go ahead and replace?
The manual has you remove the RF subchassis with the tuning dial set to “00-972”.  Then, before re-installing, it calls to check the sync of the cams on the back of the unit against their witness marks with the dial adjusted to “02 000”
If I can’t rotate the megacycle change gear with the subchassis extracted, how am I supposed to complete this task?
Thank you,
-Alex

Jacques Fortin <jacques.f at videotron.ca> schrieb am So. 15. März 2026 um
22:40:

> Hi Alex,
> To complement Barry's answers, removing the RF deck with the "green" 
> gear not in place usually ends with the need to resynchronize the gearbox.
> For the springs, see the attached design specifications document.
> I have found some suitable substitutes, but never used those in my own
> R-390 and R-390As.
> If ever you want to try those, let me know.
>
> 73, Jacques, VE2JFE in Montreal
>
> Alex,
> The green gear doesn't exactly "lock" the gear train.  I keeps the 
> sections synchronized with each other when the RF deck is removed.  It 
> is normal for it to rotate like that.
> Getting the backlash set is a bit fidgety.  I found it helpful to have 
> something that can keep the tension and the teeth of both halves 
> matched up during the process.  If I recall correctly, I loaded them 
> and then pushed a flat-blade screwdriver in the teeth to hold them 
> until I could get them meshed.  i think that's necessary for both 
> sides.  Others may have better advice for how to do that.
> I don't know what might be used as replacement springs.
> Thanks,
> Barry - N4BUQ
>
>
> On Sun, Mar 15, 2026 at 8:28 AM Alex Hopper via R-390 < 
> r-390 at mailman.qth.net>
> wrote:
>
> > Hello All,
> >
> > Following my manual, I carefully removed the font panel on my 
> > R-390/URR
> > (non-A) last night.  I am at a point where I would like to begin the 
> > process of removing the RF deck.
> >
> > How exactly is the green gear intended to 'operate'.  While the RF 
> > deck was still in place last night, I attempted to affix the green 
> > gear to it's post to the right of the KC change gear.  The green 
> > gear still moved in this position when the KC change was rotated.
> > Does the green gear work by locking the entire tuning mechanism only 
> > after the RF
> deck is removed?
> >
> > What other pitfalls should I look out for?  Reading the manual makes 
> > the process of replacing the RF deck sound MUCH more difficult.  Is 
> > meshing the gears back together as complex as it sounds?
> >
> > Finally, when the deck is out I would like to replace at least a few
> rather
> > rusty and tired looking springs on the slug racks.   Is there a specific
> > spring size/tension I should be looking for?
> >
> > Thanks,
> > -Alex
>