[Elecraft] K2 receiver problem - AGC alignment, CAL S LO/HI

Fri Nov 11 11:06:38 EST 2005

Hi

The last K2 I built had strange AGC and S-meter operation that sounds like 
the one you are working on. The problem was I had skipped installing the 
toroid RFC11 on the bottom of the board. It is amazing the K2 worked at all 
but it received fairly well. I could even hear the 1 uV signal from the XG2. 
Anyway installing the RFC solved the problem. May be worth a look to see if 
you have the same problem

Don Brown
KD5NDB

----- Original Message ----- 
From: "Gerhard Schwanz" <gerhardschwanz at yahoo.de>
To: <Elecraft at mailman.qth.net>
Cc: <w3fpr at arrl.net>
Sent: Friday, November 11, 2005 2:23 AM
Subject: [Elecraft] K2 receiver problem - AGC alignment, CAL S LO/HI

> Hi list,
> hi all those who answered my first question.
>
> I had 4V at Pin5 U2. So I replaced R1 with a pot of 50k and set it to 
> 3.65,
> 3.72 and 3.8V. It got better for sure. The difference between AGC on and 
> off
> is in all cases noticable, but slightly. But I think it's significant,
> because...
>
> When I CAL S LO and exit it then immediately 1-2 bars of the s-meter start
> lighting. So I guess AGC sets in. And this should not be the case, I 
> guess?
> Any idea?
>
> Have a nice day,
>
> Gerhard
>
>
> ----- Original Message -----
> From: "Don Wilhelm" <w3fpr at earthlink.net>
> To: "GS" <gerhardschwanz at yahoo.de>
> Sent: Wednesday, November 09, 2005 3:35 PM
> Subject: RE: RE: [Elecraft] K2 receiver problem
>
>
> > Gerhard,
> >
> > If you have a K2 with serial number greater than 3000, the AGC 
> > adjustment
> > pot is on the Control Board near the right end - the designation is R1.
> >
> > For K2 with SN under 3000, there is no pot, and R1 is a fixed resistor.
> > Same procedure applies - change the value of R1 to set the AGC 
> > threshold.
> > It is easy to substitute a temporary pot (50K will do fine) to make the
> > adjustment - once the right value is found, solder in the closest value
> > fixed resistor.
> >
> > In my experience, the fixed resistor that one would end up with will 
> > vary
> > between 33K at the low end and 47k at the high end.
> >
> > BTW, if this receiver has worked properly before and suddenly developed
> this
> > problem, look more closely for a failed component - it will likely be in
> the
> > AGC area - see the control board schematic in the lower left corner.
> >
> > 73,
> > Don W3FPR
> >
> > > -----Original Message-----
> > > From: GS [mailto:gerhardschwanz at yahoo.de]
> > > Sent: Wednesday, November 09, 2005 9:48 AM
> > > To: w3fpr at arrl.net
> > > Subject: Ant: RE: [Elecraft] K2 receiver problem
> > >
> > >
> > > Hi Don,
> > >
> > > I can't find how to set the AGC threshold for optimum
> > > receiver sensitivity, neither in the manual nor is
> > > there any hint in the circuit. At least not for me ;-)
> > >
> > > Only threshold mentioned in the manual is for the
> > > NB...
> > >
> > > WHAT do I have to adjust to achieve max. voltage at U2
> > > pin 5, ctrl board?
> > >
> > > Thanks!!!
> > >
> > > Gerhard
> > >
> > >
> > > --- Don Wilhelm <w3fpr at earthlink.net> schrieb:
> > >
> > > > Gerhardt,
> > > >
> > > > It sounds like the AGC Threshold is not set
> > > > properly.
> > > >
> > > > I would proceed by first checking the alignment of
> > > > the bandpass filters in
> > > > Transmit mode (at 2 watts) and then set the AGC
> > > > Threshold for optimum
> > > > receiver sensitivity - with no antenna connected and
> > > > AF and RF Gains set to
> > > > max, adjust for the highest voltage at Control Board
> > > > U2 pin 5 which yields
> > > > no change in the audio noise when switching the AGC
> > > > between OFF and ON.
> > > > That will usually result in a voltage in the range
> > > > of 3.65 to 3.8 volts at
> > > > U2 pin 5.  Set the S-meter end points (CAL S Hi and
> > > > CAL S-Lo) after setting
> > > > the threshold.
> > > >
> > > > If that does not cure the problem, then look for a
> > > > problem in the IF receive
> > > > chain - that will be where the signal tracing is
> > > > required, follow the
> > > > p[rocedure for receiver signal tracing in the
> > > > Troubleshooting appendix of
> > > > the K2 manual.
> > > >
> > > >
> > > > 73,
> > > > Don W3FPR
> > > >
> > > > > -----Original Message-----
> > > > >
> > > > > got a K2 from another OM on my workbench. It's got
> > > > a
> > > > > receiver problem and I just want to make sure I do
> > > > the
> > > > > checks in the correct order and I'm looking for
> > > > hints,
> > > > > if available!
> > > > >
> > > > > Thanks in advance!
> > > > >
> > > > > So here's the problem and what I want to do. It
> > > > seems
> > > > > the receiver runs with "handbrake on". So the
> > > > s-meter
> > > > > shows 3 bars without an antenna but the rf gain is
> > > > > fully clockwise. I can reduce signals to zero
> > > > (using
> > > > > RF gain) with this K2 which I can't using my own
> > > > K2.
> > > > > So mine has a higher sensitivity.
> > > > >
> > > > > Any idea what's wrong?
> > > > >
> > > > > What I want to do:
> > > > > - s-meter alignment
> > > > > - I.F. amplifier alignment
> > > > > - (maybe band pass alignment)
> > > > > - signal tracing receiver and synthesizer
> > > > >
> > > > > Kind regards
> > > > >
> > > > > Gerhard
> > > > > DH3FAW
> > > > >
> > > >
> > > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > ___________________________________________________________
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> > > --
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> 11/8/2005
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> >
>
>
>
>
>
>
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