Kevin,
It is normal to see a higher response touching a random, wire to C6
compared to touching the same wire to W6. The C6 location is a high
impedance point while the W6 and D6 locations are low impedance - the
capacitive dividers (C7,8 and C4,5) reduce the impedance.
The end of a random wire is a high impedance and matches better at C6.
If you were connecting the center conductor and ground the shield of a
properly matched feedline close to the test point, you would likely find
a better response at W6 than at C6.
That is why that testing technique is called "Cheap and Dirty" - it does
have some eccentricities that the user needs to be aware of (like this
one), but overall is a quick troubleshooting aid.
If you are getting about the same response at D6 and W6, then the
bandpass filter is probably OK.
73,
Don W3FPR
Kevin Cozens wrote:
> Greetings.
>
> I have barely used my K2 going on about two years now. It seemed to work
> well when I first got it off the person who had assembled it. I got
> occasional comments about good audio when operating on SSB. I then
> started applying the mods to bring it in line with the post 3000 serial
> number units, applied the PLL stability mode, and replaced the crystals
> with a more closely matching set, and completely re-aligned the radio.
>
> Since then, the radio seems to have become slightly deaf, and I also
> have some issues with transmit audio. I've considered selling it to
> someone who could fix it and starting over. Having acquired a good
> digital storage oscilloscope some months back, I'm going to have another
> shot at trying to fix the problems. I'll start by working on the receive
> issues.
>
> I'm planning to get one of the Elecraft signal generator kits to help
> with tracking down the receiver issues. Since I don't currently have
> one, I'm starting with the cheap and dirty signal tracing notes from
> Tom, N0SS. I pulled out the KSB2 and disconnected the KAT2 to eliminate
> them as a source of problem. I have noticed one odd thing when using a
> random length of wire and touching one end of it to the indicated test
> points.
>
> Touching the wire to either side of C6 (RF Board page 3), the S meter
> reading on the front panel goes up by about 2 LED's. What is odd is that
> if I touch W6, or either end of D6 (the previous and next points in the
> signal chain) I don't see this level of increase in signal level.
>
> This isn't making sense to me right now. I would think I would get the
> same signal level increase at either W6, or D6, but not at neither point
> compared to both sides of C6. Could this indicate bad, or wrong value
> caps, for C5 and/or C7? Any other thoughts about this rather odd
> behaviour? Seems to be pointing towards something to investigate further
> but I hope I don't have to removed that bottom rear panel as its more of
> a pain to remove.
>
>
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