[R-390] MHZ gear clamp busted

Thu, 19 Dec 2002 07:12:54 -0500

Why not rebuild the whole geartrain?  You will be happier
if you do.  I have a complete rebuild and alignment 
instructions with many high quality pictures at:
http://www.r-390a.net/faq-refs.htm
Just scroll down to tutorials and you will see the file there.
It is a PDF file that you can download and print out.
If you have any specific trouble I will be happy to help
you.
5 week old twins Yikes!!!  I have a 18 month old and a 
5 year old and time is really in short supply around here.
They are a whole lot of fun (and headaches!!).
Enjoy them!!!!

Scott 

----- Original Message ----- 
From: "Mark Richards" <[email protected]>
To: "'Walter Wilson'" <[email protected]>; <[email protected]>
Sent: Thursday, December 19, 2002 7:02 AM
Subject: RE: [R-390] MHZ gear clamp busted

> Walter and Matt - many thanks for your excellent advice!  I suppose
> that, given I must at least partially disassemble the gears, it's not a
> bad idea to clean and re-lubricate everything, correct?  I have read
> somewhere that once this is done the performance of the tuning can be
> quite smoothe.
> 
> The pictorial for disassembly seems straightforward enough.  We'll have
> at it!
> -m-
> 
> 
> 
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]
> On Behalf Of Walter Wilson
> Sent: Thursday, December 19, 2002 05:58
> To: Mark Richards
> Cc: [email protected]
> Subject: Re: [R-390] MHZ gear clamp busted
> 
> > So in summary my questions are (1) how to replace the MHZ gear clamp
> and
> > (2) how should the MHZ gearing be engaged and (3) how does the
> > anti-backlash work.
> 
> 
> Mark,
> You will have to remove the front panel.  No real difficult steps here.
> First, set the KC setting at +000 (that's one KC above 999), and the MC
> at
> 7MC.  Just remember to loosen the 1/4 shaft nut around the dial lock,
> and
> rotate the dial lock about 1/4 turn to disengage it from the KC disc.
> Shine
> a flashlight down in there, and you'll see what you need to do.  Then
> loosen
> the 13 screws that secure the front panel and remove the knobs, and
> you're
> ready to go.  Oh, and you'll have to loosen the clamps the secure the
> Bandwidth and BFO shafts to their respective shafts on the IF deck.  Now
> pull the front panel loose from the MC and KC and AGC shafts, and tilt
> forward.  It helps if the R-390A is sitting on a platform about 2 inches
> higher than your workbench or table, so that when the panel lays
> forward,
> its handles will rest straight against the working surface.
> 
> Now you have a more challenging task.  If you set your frequency at
> 7+000,
> then all your camshaft marks should be aligned with the points of the
> camshafts.  This was done just in case you move something during these
> next
> steps.  You'll have to remove the veeder root counter, and all the gears
> in
> front of the front gear plate.  Then you will be able to loosen the
> screws
> on the front plate and "gently" remove the plate.  You should now have
> access to the MC gear clamp.  After replacement and reassembly, check to
> see
> that the cams are still aligned, which will be the case if nothing bad
> happened while the front plate was off.
> 
> The MC gearing engages both of the split gears to the other wider gear,
> with
> about two gear-teeth of rotation to stretch the spring.  Both teeth
> engage
> in the middle of the wider gear, and the spring is stretch if you get it
> back on correctly.  The spring tension works in a fashion to pull the
> two
> gears to fill the entire width of the space between the gears of the
> wider
> brass gear.  It essentially gives this split gear a variable width
> tooth,
> that stretches to fill any gap that might otherwise exist.  IF the gear
> train moves smoothly, then this amount of spring tension is enough to
> overcome any gear friction.  If the gear train has a lot of gear
> friction
> somewhere, then the anti-backlash features are basically defeated by the
> friction (that is stronger than the spring tension of the split gear).
> 
> Your 7MC problem is very often due to C327, which is a 100pF capacitor.
> Your capacitor kit should contain a 100pF capacitor to replace it with.
> While it's not always a problem, I'd personally never go to the trouble
> to
> remove the RF deck without replacing this capacitor, the three paper
> capacitors, and checking all the resistors underneath (there are several
> resistors that seem to be persistant problems).
> 
> Walter Wilson - KK4DF
> http://r-390a.us
> (REAL Radios: R-390A, R-390, T-368E, Ranger, Thunderbolt, KWM-2A)
> 
> ----- Original Message -----
> From: "Mark Richards" <[email protected]>
> To: <[email protected]>
> Sent: Thursday, December 19, 2002 12:15 AM
> Subject: [R-390] MHZ gear clamp busted
> 
> 
> > Hello to the R-390 group.  I am so pleased that there are still
> > enthusiasts of this fine radio active.  May I draw on the knowledge
> > herein?
> >
> > I have stolen an hour from our demanding new twins :) (5 weeks old)
> and,
> > while my wife and the children were snoozing, managed to begin some
> work
> > to replace the MHZ Gear Clamp on my R390a.  The MHZ knob never worked
> > since I acquired this radio years ago.  I never used it seriously and
> > planned to rebuild it someday.  Someday has arrived.  Besides, my life
> > has to consist of more than changing diapers and burping babies!
> >
> > Through the good auspices of David Medley, I've secured a gear clamp.
> > Now I need some good advice before I get myself into a deeper pickle.
> >
> > It appears that it is impossible to replace the MHZ Gear Clamp without
> > actually disassembling the entire shaft.  I began this work by
> removing
> > (actually breaking) the snap-ring on the end of the MHZ shaft and then
> > tried to pull the shaft out, using the MHZ knob.  Hopefully this is a
> > common ring that I can get at the local auto parts store :)  Anyhow,
> > this method failed as it appears that a component of (the very novel)
> > mechanical turns limiter is fastened to the shaft.  I cannot determine
> > how it's fastened, but it's definitely on there.  Perhaps there is a
> pin
> > driven to hold it in place?  It does not appear possible to remove it
> > with simple tools.
> >
> > Therefore it appears my only option is to remove the front panel of
> the
> > radio and then disassemble the front portion of the gear mechanism
> (the
> > Veeder-Root counter assembly).  Perhaps then I will have access so
> that
> > I can slip on the new clamp?
> >
> > I want to remove the front panel anyway and perform some of the
> cleaning
> > steps you recommend but first wanted to make sure the unit was
> > electrically sound before I messed up the mechanics.
> >
> > Would any of you experienced folks be able to offer me some sound
> > advice?
> >
> > Oh, I did manage to power up the radio and found it to be actually in
> > fairly good working order.  It does appear that the sensitivity drops
> > off dramatically below 7 MHz, however.  I did not make measurements -
> > these were simply done with a signal generator attached to a wire -
> yet
> > the differences were dramatic enough to suggest that there is a
> problem
> > below 7 MHz.
> >
> > I have a capacitor rebuild kit so once I get the MHZ gear back in
> > service, I will strip the radio down, clean it up and replace the
> pesky
> > capacitors.
> >
> > One more question - regarding the actual MHZ gear.  It is assembled,
> as
> > you all know, as two thin gears, independent of each other but
> connected
> > by a small spring.  I understand this is an "anti-backlash" mechanism.
> > When I reassemble things should BOTH of the MHZ gears be engaged with
> > the gear they connect to or just one?  How does the anti-backlash
> > mechanism actually work?
> >
> >
> > So in summary my questions are (1) how to replace the MHZ gear clamp
> and
> > (2) how should the MHZ gearing be engaged and (3) how does the
> > anti-backlash work.
> >
> > Thanks for your kind help,
> >
> > Mark Richards
> > K1MGY
> >
> >
> > _______________________________________________
> > R-390 mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/r-390
> >
> 
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