[Elecraft] K2 BFO Test fails

[Don Wilhelm]

  Benny,

Actually you should have a better signal at U11 pin 6 than you do at pin 
7, but let that go for right now (we may get back to it if necessary).

So you do get the proper BFO frequency when grounding the crystals, and 
as I recall you measured a low resistance across L33, so it should have 
continuity - all that should be good.

Now, monitor the oscillation at U11 pin 6 (or pin 7) while you ground 
the side of L33 that is NOT connected to X4 and X5.
Ignore any oscillation other than the 4.9 kHz because that is what you 
are looking for.

If you get a 4.9 kHz oscillation with the low end of L33 connected to 
ground, then check the value of C172 - it should be 0.01 uF (marked 
103).  Also verify again that D37 is mounted the "right way 'round".

If you cannot get a 4.9 kHz oscillation with the lower end of L33 
grounded, inspect the soldering of those fine wires to the leads of the 
1/8 watt resistor very carefully - and make sure what you used for that 
high value 1/8 watt resistor was the correct item.  It is a very high 
value resistor, and is actually used as an effective insulator across 
L33 to both solder the fine wire leads and secure L33.  If you used 
anything else, that could cause your problems.

73,
Don W3FPR

On 12/4/2010 1:47 PM, kruegerbenny wrote:
> So, hello again.
>
> First of all i want to excuse but I give you some false informations. The
> 8.x MHz signal I measured was/is at Pin 7, not Pin 6 of U11. I did the test
> with grounding L33/X3/X4 and there's some interesting behaviour (at Pin 7):
> When I ground L33/X3/X4, the measured signal is about 7.7MHz. By removing
> the jumper(to ground), the frequency changes to 4.9MHz.
>
> After that, I changed the order of instructions:
> Now I connect the probe at P7(U11) and then ground L33/X3/X4. The result:
> Before grounding 8.02MHz, after grounding 4.9MHz (also when I remove the
> jumper)
>
> Benny
>
>