[R-390] Megacycle Change Stuck R-390

Fri May 2 12:52:44 EDT 2025

I synced the 10-1/2 turn mechanism with the shaft such that I have now have approximately 90-degrees of overtravel at each end.  I can now rotate the MC knob about halfway between 32.xxx and 33.xxx where it hits the stop.  Likewise, I can rotate the knob about half-way between 00.xxx and -99.xxx.  I think this is normal, correct?

Barry - N4BUQ

> I checked and I can rotate the MC knob CW to 32.xxx.  I checked the 10 1/2 turn
> stop mechanism and it has 11 winged "washers" and I think that's correct as it
> is labeled a "10 1/2 TURN STOP" in the manual and I have 11 washers on both the
> MC and KC shafts.  I think, however, that I may need to make an adjustment to
> my MC stop mechanism.
> 
> When I turn the MC knob CCW to 00.xxx, I only have 2 or 3 degrees overtravel
> before I hit the stop point due to the 10 1/2 stop mechanism and I think that
> may be why I have sufficient overtravel at CW end of travel to go to that extra
> MC.  I'm thinking that when I reach 00.xxx in the CCW direction, I should be
> able to rotate the knob about 90-degrees before hitting the stop and if that's
> set, then I should run out of travel at the CW end before getting to 32.xxx.
> 
> Is ~90 degrees overtravel appropriate to have at the end of the CCW and CW
> rotation?  If so, I'll make that adjustment.  At this point, I don't think I've
> damaged the Geneva mechanism - at least the part that I can see from the
> underside of the chassis.
> 
> Thanks,
> Barry - N4BUQ
> 
>> It is imperative that the clockwise rotation of the megacycle shaft stops at 31.
>> This is where the ten-turn stop should lock. Any further rotation could damage
>> the Geneva mechanism.
>> 73
>> Don WC4G
>> Sent from my iPhone
>> 
>>> On May 1, 2025, at 20:13, Tom via R-390 <r-390 at mailman.qth.net> wrote:
>>> 
>>> The radio only tunes to 32 mhz. So the mhz dial will stop at 31 and the top end
>>> of that band is 32 mhz
>>> 
>>> Tom
>>> W3TA
>>> 
>>> -----Original Message-----
>>> From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On Behalf Of
>>> Barry
>>> Sent: Thursday, May 1, 2025 7:34 PM
>>> To: Alex Hopper <ahopper0216 at gmail.com>
>>> Cc: R-390 Mailing List <r-390 at mailman.qth.net>
>>> Subject: Re: [R-390] Megacycle Change Stuck R-390
>>> 
>>> Alex,
>>> 
>>> I just realized that I've been telling you to rotate the MC knob CW to "31.xxx".
>>> That should be "32.xxx". Apologies. I had it in my head that the radio only
>>> tuned to 32 MHz but it will turn to 33 MHz (or, perhaps, more formally
>>> "31.999.9")! Sorry for the misinformation. I hope I didn't cause you to do
>>> something incorrect.
>>> 
>>> Barry - N4BUQ
>>> 
>>>> From: "Barry" <n4buq at knology.net>
>>>> To: "Alex Hopper" <ahopper0216 at gmail.com>
>>>> Cc: "R-390 Mailing List" <r-390 at mailman.qth.net>
>>>> Sent: Thursday, May 1, 2025 4:24:55 PM
>>>> Subject: Re: [R-390] Megacycle Change Stuck R-390
>>> 
>>>> Yes. The 10-turn stop is pinned to the shaft so the idea is to rotate
>>>> the knob which will still rotate the 10-turn stop.
>>> 
>>>> In your case, since it's stopping you before it should in the CW
>>>> direction, I would rotate the knob CCW to the "00.xxx" position,
>>>> loosen the clamp, rotate shaft farther CCW until the stop hits, rotate
>>>> slightly back CW, and tighten the clamp. After that ensure there is
>>>> about the same amount of overtravel on the fully CW direction (from "31.xxx" as
>>>> there is in the fully CCW direction.
>>> 
>>>> Again, I think there's a correct procedure to do this in the manual
>>>> but this should work as well.
>>> 
>>>> Barry - N4BUQ
>>> 
>>>>> All - is the adjustment point for the 10-turn stop the
>>>>> yellow-highlighted “collar” on the shaft of the megacyle change as
>>>>> pictured? There is a small bristol head screw on it.
>>>>> -Alex
>>> 
>>>>> Barry < [ mailto:n4buq at knology.net | n4buq at knology.net ] > schrieb am
>>>>> Do. 1. Mai
>>>>> 2025 um 12:04:
>>> 
>>>>>> Alex,
>>> 
>>>>>> There should be very little CCW overtravel past the lower end and
>>>>>> about the same amount of CW overtravel at the upper end. Sounds like
>>>>>> you've found the problem and, provided you have the correct Bristol
>>>>>> wrench, it should be fairly easy to correct.
>>> 
>>>>>> Barry - N4BUQ
>>> 
>>>>>>> Barry,
>>>>>>> with the MC dial set to "00" I am able to rotate the MC knob CCW
>>>>>>> and nearly get the dial to read "99" but it doesn't 'click' into
>>>>>>> place. I'll have a look at it (power OFF, of course).
>>>>>>> -Alex
>>> 
>>>>>>> On Thu, May 1, 2025 at 11:17 AM Barry < [ mailto:n4buq at knology.net
>>>>>>> | n4buq at knology.net ] > wrote:
>>> 
>>>>>>>> Alex,
>>> 
>>>>>>>> I think there's a procedure to do that in the manual and that
>>>>>>>> might be best to follow; however, are you able to rotate the MC
>>>>>>>> knob to where the two left-hand digits on the counter are at "00"
>>>>>>>> and then continue CCW rotation one more click? If so, then that's another
>>>>>>>> indication the ten-turn stops are off.
>>> 
>>>>>>>> If everything else is correct, then when the left two digits are
>>>>>>>> at "00", you should be able to rotate the knob just a few degrees
>>>>>>>> CCW beyond that but no more and when the left two digits are at
>>>>>>>> "31", you should be able to rotate the knob just a few degrees CW
>>>>>>>> but no more than that. If those conditions are not met, then
>>>>>>>> loosening the clamp on the ten-turn stop and moving the stop
>>>>>>>> mechanism to get those two stop points correct should be all that you need to
>>>>>>>> do.
>>> 
>>>>>>>> Good luck with it! And, at the risk of sounding overly-concerned,
>>>>>>>> please make sure the radio isn't powered up when you do that (or,
>>>>>>>> at least, take the proper precautions).
>>> 
>>>>>>>> Barry - N4BUQ
>>> 
>>>>>>>>> Barry - it is a R-390 not a 390A. How does one adjust those
>>>>>>>>> points on the MC shaft?
>>>>>>>>> -Alex
>>> 
>>>>>>>>> On Thu, May 1, 2025 at 11:01 AM Barry < [
>>>>>>>>> mailto:n4buq at knology.net | n4buq at knology.net ] > wrote:
>>> 
>>>>>>>>>> If you turn the radio over, those stops are quite visible (there
>>>>>>>>>> is a set of them on both the KC and MC shafts).
>>> 
>>>>>>>>>> BTW, is this an R-390 or R-390A? It shouldn't make much
>>>>>>>>>> difference for this but would be good to know.
>>> 
>>>>>>>>>> Barry - N4BUQ
>>> 
>>>>>>>>>>> Thank you both! Is adjusting the 10-turn stop something that
>>>>>>>>>>> would require removal of the crystal oscillator or RF modules?
>>>>>>>>>>> -Alex
>>> 
>>>>>>>>>>> On Thu, May 1, 2025 at 10:53 AM Barry < [
>>>>>>>>>>> mailto:n4buq at knology.net | n4buq at knology.net ] > wrote:
>>> 
>>>>>>>>>>>> Hi Alex,
>>> 
>>>>>>>>>>>> There are a series of "wings" on the shaft that determine
>>>>>>>>>>>> where the stop point should be at both ends of rotation (I
>>>>>>>>>>>> think those limit the shaft to just a tad over 10 turns
>>>>>>>>>>>> end-to-end). If all of those are completely stopped against
>>>>>>>>>>>> each other, then that would cause this and the solution would
>>>>>>>>>>>> be to loosen the clamp and adjust those stopping points. If
>>>>>>>>>>>> the stop point is reached but those "wings" can still be
>>>>>>>>>>>> rotated slightly with your fingers (be aware there is power near that point so
>>>>>>>>>>>> best to unplug the radio to try this), then something else might be a problem
>>>>>>>>>>>> but I think the 10-turn stop is the problem.
>>> 
>>>>>>>>>>>> Good luck,
>>>>>>>>>>>> Barry - N4BUQ
>>> 
>>>>>>>>>>>>> Hi All,
>>> 
>>>>>>>>>>>>> I have an R-390 that has recently been restored. It is
>>>>>>>>>>>>> performing very well, with one exception...
>>> 
>>>>>>>>>>>>> Last night I attempted to tune up through all of the
>>>>>>>>>>>>> megahertz bands all the way to 32 MgHz for the first time. I
>>>>>>>>>>>>> got to '30' on the megacycle change knob, and the knob
>>>>>>>>>>>>> wouldn't rotate any further to 31. I could get it to go
>>>>>>>>>>>>> slightly towards 31, but it was obviously stuck and I didn't want to attempt to
>>>>>>>>>>>>> jam it.
>>> 
>>>>>>>>>>>>> What would potentially be the cause for this being stuck?
>>> 
>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>> -Alex
>>>>>>>>>>>>> ____________________________________________________________
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