[R-390] Megacycle Change Stuck R-390

Thu May 1 20:11:35 EDT 2025

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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