K2 S/N 4240 On the Air

[g.c.hart]

Mostly everything works fine, but...

1) Still appears to be a problem with the AGC/S-meter calibration because the S-meter is continuously "pegged" on rightmost LED.

The RF Gain control appears to have no effect although I've confirmed that R4 (front panel RF Gain control) seems to function properly at the RF Board J6-6 connector.

U12 pin 5 (voltage controlled by RF Gain control) reads: 3.192 Vdc. when RF Gain fully clockwise, and remains unchanged when RF Gain control is turned to fully counterclockwise.

The AGC voltage is: 3.75. The S-meter calibration steps seemed to go fine with S LO and S HI adjustments.

When the radio is first turned on various LEDs on the bargraph display are lit before settling on the rightmost LED.

I have inspected the solder joints on the AGC/S-meter circuit components, and RP6 is correct.

2) The WWV 10 MHz station is received fine, but I'm not sure whether the PLL needs to be re-calibrated. The transmission seems zero-beat at 10.000.00 MHz cw mode, FL1 1.50, but is zero-beat on 10000.50 MHZ, USB, FL2 2.00. Do I need to re-calibrate the PLL per procedure on p. 101 (Frequency Calibration Techniques)?

Thanks.

Gary
N0AGH
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[Don Wilhelm-3]

Gary,

AGC/RF Gain problem:
With the Front Panel, Control Board and RF Board assembled together, check
the resistance to ground from Control Board P1 pin 6 to ground.  It should
read about zero ohms with the RF gain at full clockwise and somewhere in the
vicinity of 4 to 5 K with the RF gain at the full counterclockwise position.
If the resistance is significantly higher that that, look for an unsoldered
connection, and if it stays near zero ohms look for a short to ground.

If all is well at Control board P1 pin 6, look carefully at the soldering of
R1 and RP6 on the control board.  The voltage at U2 pin 5 should change with
the setting of the RF Gain and with the setting of the AGC Threshold pot.
This is a simple resistive network with 2 pots and an 8 volt voltage source,
so you should be able to set the voltage at U2 pin 5 most anywhere from
below 3 volts up to above 3.8 volts.

Also, check the orientation of D1 on the control board - if it is backwards,
it could cause the symptoms similar to those you report.

2). WWV dial calibration:  - yes it seems like you need to re-set the 4 MHz
reference oscillator and then do both CAL PLL and CAL FIL.  For details, see
my website www.qsl.net/w3fpr article on K2 dial calibration - you will find
more information than you may have wanted to know about it.

73,
Don W3FPR

----- Original Message -----

>
> 1) Still appears to be a problem with the AGC/S-meter calibration because
> the S-meter is continuously "pegged" on rightmost LED.
>
> The RF Gain control appears to have no effect although I've confirmed that
> R4 (front panel RF Gain control) seems to function properly at the RF
> Board J6-6 connector.
>
> U12 pin 5 (voltage controlled by RF Gain control) reads: 3.192 Vdc. when
> RF Gain fully clockwise, and remains unchanged when RF Gain control is
> turned to fully counterclockwise.
>
> The AGC voltage is: 3.75. The S-meter calibration steps seemed to go fine
> with S LO and S HI adjustments.
>
> When the radio is first turned on various LEDs on the bargraph display are
> lit before settling on the rightmost LED.
>
> I have inspected the solder joints on the AGC/S-meter circuit components,
> and RP6 is correct.
>
> 2) The WWV 10 MHz station is received fine, but I'm not sure whether the
> PLL needs to be re-calibrated. The transmission seems zero-beat at
> 10.000.00 MHz cw mode, FL1 1.50, but is zero-beat on 10000.50 MHZ, USB,
> FL2 2.00. Do I need to re-calibrate the PLL per procedure on p. 101
> (Frequency Calibration Techniques)?
>
> Thanks.
>
> Gary
> N0AGH
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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