[Elecraft] Inoperable S-Meter

[Ron D'Eau Claire]

Rich (reading over Don's shoulder here)...

Does your S-meter move from min to max as you run the RF gain up and down? 

That would help pin down the issue to either the I.F (in the K2 that's
called "RF" gain) gain control voltage or the AGC system itself. The RF Gain
pot does adjusts the same voltage manually that the AGC system is supposed
to control automatically.

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Don Wilhelm
Sent: Saturday, February 18, 2006 5:40 PM
To: recarter at adelphia.net
Cc: Elecraft at mailman.qth.net
Subject: RE: [Elecraft] Inoperable S-Meter


Rich,

Yes, those numbers look a lot more sensible, and furthermore, those DC
readings seem to be close to normal.

I suggest you get out your 'scope while driving the K2 with a healthy sized
input signal and see if you can find any IF energy at the input of the
control board U1 mixer - that should in turn produce an output signal at the
output of the AGC mixer at about 155 kHz.  That 155 kHz signal should pass
through U2 from pin 6 to pin 7 and the AC signal should be rectified by
diode D1, adding to the DC bias from the voltage at U2 pin 5 and modifying
the DC level at the base of Q12 with the signal strength - stronger signals
will increase the Q12 base voltage and weaker signals will allow it to drift
toward the setting supplied by the DC Biasing controlled by the AGC
Threshold pot setting.

I don't know the capabilities of your 'scope, so I don't know how low a
signal level you can measure.  There is a chance that you do not have a good
path between the IF takeoff point (IF OUT) after the varaible filter and the
input to Control Board U1 pin 1.  If your 'scope can measure small signals,
it would be informative to see if the signal is getting to the AGC mixer
input.

Even if you cannot observe the actual signals at U1 with your 'scope, you
should see the voltage at the base of Q12 increase with a steady strong
signal applied to the K2 input.

Once you have verified that the AGC is responding to changes in signal
strength, we can look at the S-meter problem if it still is present.

73,
Don W3FPR


> -----Original Message-----
>
> Don
> I thought the numbers looked high, but the regulator is not 
> adjustable.  I measured it again and found the 5v regulator high too.  
> The batteries in my voltmeter are low, causing the readings to look 
> high.  Here they are again with a fresh battery.
>
>     U2-1     3.7v
>     U2-2     3.7v
>     U2-3     3.6v
>     U2-4     0v
>     U2-5     3.8V
>     U2-6     3.8v
>     U2-7     3.8v
>     U2-8     8.0v
>     Q12-E    7.8v
>     Q12-B    3.66v
>     Q12-C    3.60v
>
> Thanks for your time
> Rich - KE1EV
>
>
> -----Original Message-----
>
> Rich,
>
> It would seem your problem extends beyond the S-meter.  For starters, 
> I don't like the 9.0 volts that you report on U2-8, that is the 
> voltage rail direct from the 8 volt regulator, so forget about the 
> S-meter for the moment and start by measuring the voltage regulator 
> U4.  Once that voltage is within range (8 volts +/- 10%) you can 
> re-check the AGC Threshold setting and see if the S-meter works.
>
> The 8R voltage is also quite high, but the regulator may be the root 
> cause of all your problems - fix the regulator problem first.
>
> 73,
> Don W3FPR
>

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