[R-390] Megacycle Change Stuck R-390

[Barry]

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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