[R-390] Dumb Mechanical Alignment question

Sat Jul 18 12:15:52 EDT 2026

Don’t worry, I won’t do a thing!! But all this happened after I mechanically disasssembled the RF deck. 
Sent from my iPhone

> On Jul 18, 2026, at 11:55 AM, n4buq <n4buq at knology.net> wrote:
> 
> Wait.  If stations are at the right places on the dial, then moving the PTO may be wrong thing to do.  With the upper/lower frequencies being what they are, I don’t know how that’s happening.  Please wait for others to chime in as my advice may not be completely correct.  Apologies.
> 
> Barry - N4BUQ
> 
>> On Jul 18, 2026, at 10:47 AM, Paul Roche <rochep at comcast.net> wrote:
>> 
>> Thanks Barry. That sounds like something even I can do! Going out of town for the night but will get to it soon. I will read more about how all this would make my receiver appear “deaf” but the stations are still coming in at the right position on the dial.
>> 
>> So set everything to 7.000 (not plus), lock gears, loosen clamp and then without electrocuting myself turn the PTO shaft till it reads 3.455. That’s a start.
>> 
>> Thank you so much!!
>> Sent from my iPhone
>> 
>>>> On Jul 18, 2026, at 10:52 AM, Barry <n4buq at knology.net> wrote:
>>> 
>>> Paul,
>>> 
>>> From those numbers, it appears the PTO is out of sync with the rest of the RF deck by about 2.5 turns (there's theoretically 100kc change per one revolution of the PTO).  That likely happened while the RF deck was removed.
>>> 
>>> One way to resolve that is to set the frequency lock to prevent the gears, etc., from turning, loosen the forward clamp of the Oldham coupler and rotate the coupler while monitoring the PTO's frequency to get the proper frequency at a given dial reading.  For example at 7.000, you would rotate it so that the PTO's frequency is at 3455kc.  Then retighten the Oldham clamp and relax the frequency lock.
>>> 
>>> While this can work, there may be a better way to do this that I'm not thinking of and perhaps wait to see what others can suggest to rectify the problem.
>>> 
>>> 73,
>>> Barry - N4BUQ
>>> 
>>>> Just measured the PTO output on 7.000+ and it is 2.716 MHz at 7.000+ and 3.682
>>>> MHz at 7.000. So that is off, I am reading Chapter 6 to figure out what to fix.
>>>> But checking the Crystal Oscillator Sub Chassis bandswitch as described in
>>>> manual 6.2.5.5 I get a value of -4V at test point E210 in Standby but in MGC or
>>>> AGC position it is ZERO! I wouldn't even know what to check but this seems bad.
>>>>>> On 07/16/2026 9:02 PM EDT Paul Roche via R-390 <r-390 at mailman.qth.net> wrote:
>>>>> 
>>>>> 
>>>>> Quick update. That paper is over my head.
>>>>> But I used musical generator and fed in a modulated 1 VOLT SIGNAL into antenna
>>>>> terminal (that’s what it took for me to hear the tone). I could find the tone
>>>>> at 0.9 MHz , 2.9 MHz, 4.9 MHz, 6.9 MHz, etc up to 28 MHz. Heard my tone on EACH
>>>>> frequency and jiggling the MHz knob made signal come in better on most of them.
>>>>> So I think that’s good. But signal barely audible at 1 volt!!!
>>>>> 
>>>>> I’m not gonna do anything for a while.
>>>>> Sent from my iPhone
>>>>> 
>>>>>> On Jul 16, 2026, at 6:16 PM, Jim Whartenby via R-390 <r-390 at mailman.qth.net>
>>>>>> wrote:
>>>>>> 
>>>>>> Larry's paper on oscillator levels is applicable to both the R-390/URR and the
>>>>>> R-390A/URR?Regards,Jim
>>>>>> Logic is a systematic method of coming to the wrong conclusion with confidence.
>>>>>> Murphy
>>>>>> 
>>>>>> On Thursday, July 16, 2026 at 04:03:55 PM CDT, Renee K6FSB via R-390
>>>>>> <r-390 at mailman.qth.net> wrote:
>>>>>> 
>>>>>> I thought I saw a paper by Larry a while back on osc levels and I did
>>>>>> have a copy. My memory still good...it is attached.
>>>>>> Renée
>>>>>> 
>>>>>> 
>>>>>> 
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> 