[R-390] Megacycle Change Stuck R-390

Don Heywood donwc4g at gmail.com
Thu May 1 20:55:47 EDT 2025 

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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