[R-390] RF Alignment Questions

[Jim M.]

Some random thoughts on why the 2-4 Mhz band might be weak:

Coils/trimmers badly misaligned.
Slug rack is sticking for the 2-4 Mhz RF coils.
One of the three RF cans for the 2-4 band may have an internal failure - 
they are made to be unplugged and replaced easily - the screw holding them 
to the chassis is accessed through the coil slug - with a small phillips 
head - after removing the slug rack).  Fair radio may have replacement cans. 
I have opened cans and replaced caps that were bad.  I have also seen coils 
that were fried either due to a lightening hit or a powerful nearby 
transmitter wherever the radio was used last.
Possible bad trimmer cap inside one of the RF cans for that band - give them 
a spin to loosen up any corrosion - if you cant get a double peak, then 
something is wrong in the can, either the trimmer itself or one of the fixed 
caps inside the can.
Another possibility is poor contact or corrosion on one of the switch wafers 
under the RF deck on a contact associated with that band.
If it is weak in just one segment of the band, then it may be a bad crystal 
for just that segment, such as 2 Mhz, 3 Mhz etc., or the crystal needs to be 
peaked using the associated trimmer on top of the oscillator subchassis.  If 
its the whole 2-4 band thats equally weak, its probably an RF coil. 
Alternately, if its just one segment of 2-4, the trimmer cap for the 
associated crystal could have gone bad - yes I have had to open xtal 
oscillator boxes and remove and replace individual trimmers - very time 
consuming but they do go bad.
These are just a few random ideas - good luck.
Jim N4BE


----- Original Message ----- 
From: <n4buq at knology.net>
To: <r-390 at mailman.qth.net>
Sent: Tuesday, February 27, 2007 5:25 PM
Subject: Re: [R-390] RF Alignment Questions


>
>> > 4. Would there be any great problem if I adjusted the slugs and
> trimmers
>> to WWV
>> > on the 2 mhz band and CHU on the 3 mhz band without a signal generator?
>>
>> You would be tweaking them at a single frequency.  The caps are supposed
> to
>> be tuned at one end and the slugs at the other.  I think the slugs are
>> adjusted at the lower frequency and the trimmers are adjusted at the
> higher
>> frequency.
>>
>> > As always, thanks!
>> >
>> > Joe Connor
>
> Joe,
>
> I misunderstood what you were intending to do with WWV and CHU signals.  I
> think you mean you'd use 2.5mc and 3.3mc instead of 2.2mc and 3.8mc. 
> Using
> those frequencies might get you pretty close, provided you can hear them
> with the radio out of alignment.
>
> Regards,
>
> Barry - N4BUQ
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