Receiver problem

[Evert Bakker (PA2KW)]

Hi all,

I finished the second stage of assembling the K2, (RF part 1) and
started the allign and test procedures.
I saw the S-meter stuck at the last led (nr 10) during receive and no
audio on the headphones and with the RF-Gain full CW.
(It actually doesn't make any difference if the RF-Gain is full CW or
CCW in my particular case).. I ignored this and started the alignement.
All went fine but ending up at the 40 mtr RX test, no wonder, nothing to
hear!.
The strange effect I noticed is when entering for instance the CAL mode
XFIL the audio noise comes on and the S-meter goes down.
But when leaving the calibration mode, the S meter goes high and audio
fades away, just like the RF gain is turned back on (which corresponds
with each other). I tried to calibrate the AGC Threshold and S-meter
again but as I expected, this is not a solution. It looks like an RF
-gain problem, which I didn't have when I had my first alignment.

I checked the boards for short circuits and cold solder joints but
didn't see anything (I might oversee something). Unfortunately I have no
signal generator available at the moment.

Who has got an idea ?????????

Evert, PA2KW





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[Don Wilhelm-3]

Evert,

I don't have any firm answers yet, but we can slowly get to the bottom of
this with some checks to see what is good and what might be bad.

First thing to check is the resistance from control board P1 to ground -
this is the RF Gain control line, and it should be close to zero ohms with
the RF Gain full Clockwise, and should increase in resistance as you move
the control.  This checks the path from the Control board to the RF Gain
control and all the connectors involved.  If that is good, move on.

You said that you do find some audio when in CAL FIL - so let's see what the
AGC voltage is - monitor the voltage at Control Board P1 pin 5 with the menu
set to CAL FIL and with the receiver set to normal.  You should have the
same voltage in both cases.  Let me know what voltage you measure.

Next move your finger down onto T7 while listening in the headphones (all
gains on full CW) - you should hear an increase in sound (your body is
picking up some BFO signal and you are coupling it back into the input of
the IF amp).  Try it in the menu CAL FIL and normal receive and tell me if
there is any difference.

We can go from there after you report the findings of those tests.

Perhaps better to do this off-reflector, and then report the findings to the
reflector after the problem is cured.

73,
Don W3FPR

> I finished the second stage of assembling the K2, (RF part 1) and
> started the allign and test procedures.
> I saw the S-meter stuck at the last led (nr 10) during receive and no
> audio on the headphones and with the RF-Gain full CW.
> (It actually doesn't make any difference if the RF-Gain is full CW or
> CCW in my particular case).. I ignored this and started the alignement.
> All went fine but ending up at the 40 mtr RX test, no wonder, nothing to
> hear!.
> The strange effect I noticed is when entering for instance the CAL mode
> XFIL the audio noise comes on and the S-meter goes down.
> But when leaving the calibration mode, the S meter goes high and audio
> fades away, just like the RF gain is turned back on (which corresponds
> with each other). I tried to calibrate the AGC Threshold and S-meter
> again but as I expected, this is not a solution. It looks like an RF
> -gain problem, which I didn't have when I had my first alignment.
>
> I checked the boards for short circuits and cold solder joints but
> didn't see anything (I might oversee something). Unfortunately I have no
> signal generator available at the moment.
>
> Who has got an idea ?????????
>
> Evert, PA2KW
>

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