I am having a problem aligning an S 20R. The receiver has just been
re-capped, however the problem I have been having was present before
the set was touched. (The set just has much better sensitivity and the
transformer runs cooler now). The problem I have been having is this:
When I try to align on band 3 (the only band which gives problems) the
closest I can bring it to proper alignment puts 7 Mhz at around 7.5 or
so on the dial, and 10 MHz at about 12 Mhz on the dial. I cannot bring
the dial tracking any closer than this. The other bands seem OK. I
have checked the wiring against a parts receiver and do not see any
problems. I verified that the oscillator is 455kHz above the received
frequency by checking a known working S 20R (which I have owned for 36
years). There does not appear to be any problem with the
trimmer/padder caps or the coil.

Any ideas???

This is where a grid diper is handy, since you are measuring the resonant
frequency of the circuit, without anything else. Check the resonant
frequency of the coils in both S-20R radios. At the calibrated frequency,
they should be the same.

There could be a number of problems - especially if someone has fiddled with
it. Are the coils the same? At 12 MHz, the frequency is off. I think you
will find one of these possibilities:

1. There is a unwanted fixed capacitor in the circuit.
2. the adjustable capacitor does not go down tominimum capacitance.
3. The coil is not adjustable like it was intended.
4. Someone has added turns to the coil.
5. Someone has removed the correct slug and substituted another core of
different material.

I would suspect 5 first if everything else looks normal.

Once in awhile, you will find something like that that probably slipped
through from the factory - but not likely.

73, Colin K7FM

On 3/19/06 9:03 PM, in article
, "Skyrider"
wrote:

I am having a problem aligning an S 20R. The receiver has just been
re-capped, however the problem I have been having was present before
the set was touched. (The set just has much better sensitivity and the
transformer runs cooler now). The problem I have been having is this:
When I try to align on band 3 (the only band which gives problems) the
closest I can bring it to proper alignment puts 7 Mhz at around 7.5 or
so on the dial, and 10 MHz at about 12 Mhz on the dial. I cannot bring
the dial tracking any closer than this. The other bands seem OK. I
have checked the wiring against a parts receiver and do not see any
problems. I verified that the oscillator is 455kHz above the received
frequency by checking a known working S 20R (which I have owned for 36
years). There does not appear to be any problem with the
trimmer/padder caps or the coil.

Any ideas???


I'm not familiar with that receiver, but I have a general suggestion.

Be sure you are adjusting the trimmer cap and coil slug at the correct ends
of the dial. On any band, the designer might use either the sum or
difference frequencies out of the mixer, which may call for tweaking the
trimmer (hi freq end of the loc osc) to set the low freq end of the dial,
etc.

Don

Colin and Don,

Thank you for your suggestions, however in my case I don't think they
will apply...

Unfortunately, a grid dipper is one item I do not own, so I am flying
blindly in that respect. To determine the oscillator frequency, I have
been tuning an Icom IC745 455 kHz above the target frequency and
listening for the S 20R's oscillator. As for your otber suggestions:
1. I have not been able to find any undocumented fixed caps in the
circuit. (Unless one was hidden inside the coil.....)
2. I checked the padder with a capacitor checker and it seemed to
adjust OK.
3. The coils on this receiver, unlike those on an S-40, are not
adjustable.
4. The coil does not "appear" to have been molested
5. Since there are no slugs, and no place for slugs, that wouldn't be
the case.

Since the other bands line up fine, I think the procedure I am
following should be OK.

I can't imagine something like that having slipped through from the
factory, but I suppose anything is possible...fortunatly I do have a
junker set to get the coil from, I just wanted to see if there was
anything I overlooked before removing the whole oscillator coil
sub-assemblies (probably would swap the entire units rather than take
them apart to replace one coil....)

Forgive me for questioning you, but something does not seem right. Have you
checked the good S-20R to make sure that its oscillator is 455 kHz above the
received frequency and not below?

I assume the trimmers are mica. You can roughly check the capacitance by how
tight the plates are meshed. Are the capacitors in both radios about the
same?

I still think you are aligned to the image and the method you are using is
confusing you.

Try this. Take your good S-20R and set if for say 10 MHz (wwv is good).
Then, listen to the oscillator. Assume that is 10.455 MHz. Now, take your
bad S-20R and set the dial to 10 MHz. Then, set your Icom to 10.455 and
adjust the capacitor until you hear the oscillator on your Icom. It should
be working.

Get a cheap grid dip meter - they are quite handy, even though you have
figured out a good workaround.

Colin K7FM

Just a thought about something simple you may have overlooked. Do the
end index marks on the dial line up with the extreme travel limits of
the variable cap? It might be off a little and the other bands might
have been aligned to the error where as band 3 might have less adj in
it. Mike KF6KXG

"Forgive me for questioning you, but something does not seem right.
Have you
checked the good S-20R to make sure that its oscillator is 455 kHz
above the
received frequency and not below? "

"Try this. Take your good S-20R and set if for say 10 MHz (wwv is
good).
Then, listen to the oscillator. Assume that is 10.455 MHz. Now, take
your
bad S-20R and set the dial to 10 MHz. Then, set your Icom to 10.455
and
adjust the capacitor until you hear the oscillator on your Icom. It
should
be working."

Did that. I wanted to verify that the oscillator operated above the
received frequency on band 3. (It does, same as on bands 1 and 2. It
operates at 455 kHz below received frequency on band 4).

In fact, I can align to the image and get it to line up at 7 MHz. Of
course, when I do that, the mixer and RF stages no longer track very
well, and it would be really annoying to have to turn the receiver on
its side and readjust those trimmers as you travel down the band. If I
align the correct way, the mixer and RF stages track (sorta)...better
than if I align on the image, but still not quite right (would make
sense if the oscillator is not tracking right....mixer and RF are
probably tracking fine....just not keeping in step with the
oscillator).

BTW...no need for forgiveness....without questioning it'd be danged
hard to figure out what's going on here....which is why I'm here to
begin with.

Since I have had the receiver in and out of the cabinet numerous times,
and since I have to turn the receiver chassis upside down I have to
remove the dials to keep from damaging them, I have had many
opportunities to make sure that the index marks line up correctly.

But thank you, it is a good thought....

Er...it's late, and maybe my thinking is a bit muddled, but: it sounds
to me like you need to get the oscillator freq LOWER than it is now
going. The earlier follow-on posts seem to be discussing ways to get the
oscillator freq HIGHER - unwanted extra capacitors, inability to loosen
the trimmer sufficiently, wrong slugs (which you don't have), etc. In my
muddled little mind, it seems you need MORE capacity and/or coil
inductance to get the oscillator freq LOWER, i.e. the oscillator needs
to be at 7.0 MHz + 455 KHz = 7.455 MHz rather than 7.5 MHz + 455 KHz =
7.955 MHz as you now have it. So, is there a chance that there is
supposed to be a little fixed ceramic or mica capacitor in parallel with
the adjustable trimmer cap across the oscillator coil that is open,
broken, or missing? Again, you need to get the oscillator freq LOWER,
not higher, don't you? Okay, so broken is the same as open; I said it's
late!

Good luck!
Ed Greeley

Skyrider wrote:

I am having a problem aligning an S 20R. The receiver has just been
re-capped, however the problem I have been having was present before
the set was touched. (The set just has much better sensitivity and the
transformer runs cooler now). The problem I have been having is this:
When I try to align on band 3 (the only band which gives problems) the
closest I can bring it to proper alignment puts 7 Mhz at around 7.5 or
so on the dial, and 10 MHz at about 12 Mhz on the dial. I cannot bring
the dial tracking any closer than this. The other bands seem OK. I
have checked the wiring against a parts receiver and do not see any
problems. I verified that the oscillator is 455kHz above the received
frequency by checking a known working S 20R (which I have owned for 36
years). There does not appear to be any problem with the
trimmer/padder caps or the coil.

Any ideas???

Might be worth seeing if the bandswitch is faulty, ie not shorting out
the unused coils on this band. An obscure fault, but youve looked ay
everything else....

Andrew VK3BFA.