K2 signal tracing

[John Wiener]

Well, I ordered the XG2 in the hopes that it would help me signal  
trace the receiver in order to find the cause of
low power and hi current on transmit.
Looks like that was a mistake.  Turns out I need a stronger signal  
than 50 uV.

Some might recall that I recently had to replace R50 (1.5 ohm 1/2  
watt) which I just did.

So, as it stands, I get reasonable values for PLL Reference  
Oscillilator and VCO (from page 10 of troubleshooting):

Ref Osc Output is .826Vrms,
VCO output is .307 Vrms,
VCO buffer Output is .654 Vrms

BFO Output is .592 Vrms
Cal FCTR reads 000000 with no probe connected
BFO Buffer Output is .05 Vrms

I believe the above are all normal values.
So far, so good

Now, when I get to Low Pass Filter, Bandpass Filter and T-R, it all  
goes South.
Low Pass Output is .01
T-R Switch #1 is .03
Bandpass Filter is .006
T-R #2 is .009

All are quite variable, usually starting higher and sliding down.
Are these low values due to not having a sufficiently strong signal?  
Or are they indicating one of several sources of my problems?

Can't say this is fun but I feel I AM learning.

John
AB8WH
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[Don Wilhelm-3]

John,

Follow the steps in the Transmit Signal Tracing in order (the order is
important), and stop at the first one that is too low because you have
located the first failure point - correct that failure and then move on to
the next point.

If I recall, the last time you did the transmitter signal tracing you had
good RF Voltages up to the Q6 base, but now it drops off earlier in the
transmit chain (at the Bandpass output).  So I conclude that your most
likely problem will be found in the soldering.  Check and double check the
soldering, and when you have finished that, check the soldering.

Looking at your RF voltages, it would now appear that you have lower than
expected RF Voltage first at the Bandpass filter output, so that is the
first place to look (and the only place until that has been resolved).  Try
tuning the Bandpass filter for a peak while observing the RF voltage on
jumper W6.  Do this for all bands in the proper band sequence (see the
proper band order on manual page 77 but add the 40 meter band too - peak L1
and L2 on 40 meters)  For those that are band pairs, the inductor must be
tuned before attempting to tune the trimmer capacitors - that means 30
meters must be peaked before 20 meters, 15 meters before 17 meters and 10
meters before 12 meters.

If you cannot obtain adequate RF voltage at W6 (.03 volts) at the same time
you have .2 volts or more at U9 pin 6 (buffer output), you can conclude that
something in the bandpass filter or the D1/D2 switch is incorrect.  Check
the schematic and check all the components between those two points for
proper values, diode orientation, good soldering, etc.  Other than the
diodes, there are no semi-conductor components between these two points, so
it must be a bad solder joint (most likely) or a bad component.

Low output along with High Current is normally an indicator of a problem
with the Low Pass Filter.
Check the toroid windings for the proper core types and correct number of
turns - count the turns going through the center of the core, if you count
only on the outside you may end up one turn off.
Double and triple check the capacitors in the LPF for proper values too.
Check the soldering in the LPF as well as all other places.

Be certain you are feeding a good dummy load when testing.

If you wish to do receive signal tracing, construct the oscillator shown in
the K2 manual - it can just be 'haywired' together and it should work
reliably. It has plenty of output for the task.

73,
Don W3FPR

> -----Original Message-----
>
> Well, I ordered the XG2 in the hopes that it would help me signal
> trace the receiver in order to find the cause of
> low power and hi current on transmit.
> Looks like that was a mistake.  Turns out I need a stronger signal
> than 50 uV.
>
> Some might recall that I recently had to replace R50 (1.5 ohm 1/2
> watt) which I just did.
>
> So, as it stands, I get reasonable values for PLL Reference
> Oscillilator and VCO (from page 10 of troubleshooting):
>
> Ref Osc Output is .826Vrms,
> VCO output is .307 Vrms,
> VCO buffer Output is .654 Vrms
>
> BFO Output is .592 Vrms
> Cal FCTR reads 000000 with no probe connected
> BFO Buffer Output is .05 Vrms
>
> I believe the above are all normal values.
> So far, so good
>
> Now, when I get to Low Pass Filter, Bandpass Filter and T-R, it all
> goes South.
> Low Pass Output is .01
> T-R Switch #1 is .03
> Bandpass Filter is .006
> T-R #2 is .009
>
> All are quite variable, usually starting higher and sliding down.
> Are these low values due to not having a sufficiently strong signal?
> Or are they indicating one of several sources of my problems?
>
> Can't say this is fun but I feel I AM learning.
>
> John
> AB8WH
>

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