[R-390] Megacycle Change Stuck R-390

[Barry]

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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