[Elecraft] K1 VFO problem

[Don Wilhelm]

David,

Yes, it does seem to be a problem between C8 and the MCU input on the 
Front Panel.
If you are getting good oscillation at the VFO (Q9 buffer) then check 
continuity from C8 to the base of Front Panel Q1 - that should give you 
a good check on the path continuity.  Also check resistance to ground to 
be certain there are no shorts.

The path from FP Q1 collector goes directly to the MCU pin 6, so check 
continuity there too.  Make certain that FP R11 and R12 are the correct 
values.

The VFO frequency reading and the E42 error message have nothing to do 
with U7, but after you solve the VFO counter problem, there may be 
another problem lurking if you found no oscillation at U7 pins 6 and 7 - 
hold that situation until later.

73,
Don W3FPR

On 3/4/2013 2:11 PM, David L DuPuy wrote:
> K1 VFO PROBLEM: I’m building a K1, and have reached the mid-point on
> populating the RF board, at the Alignment and Test, Part I (page 36).  All
> looks well until I get to VFO Range Test on p. 38, and I get E42 (VFO not
> functioning).  The previous resistance and voltage checks were all fine.
>
> I have indeed looked carefully for wrong components or bad solder joints,
> and all looks well.  (I’m using a Weller WP-25 iron and have plenty of
> experience with soldering, and re-checked very carefully with a quality
> magnifying glass!)
>
> I see a clean VFO signal on pin 1 of U7 (premix), and the same signal on
> the emitter of Q9 (buffer).  I see only hash on the side of C8 that goes to
> P1 pins.  The amplitude is only 0.07 volts... is it really supposed to be
> that small??!  The frequency is approximately 3030 (using analog
> oscilloscope),  which appears close to the 3090 minimum; I have not yet
> gotten to the next page where the VFO range is adjusted.
>
> On U7, pin 6 (to the crystal X1) I see a ragged, low amplitude signal which
> appears to be the  expected 15.00 MHz... but it sure is messy.  I have
> carefully checked continuity from U7 pin 6 to pin 9 on K1A on the filter
> board, and that’s fine.
>
> Can anyone tell me if this sounds like a problem upstream of Q8?  Or maybe
> a problem with U7?  Many thanks...  Sure am glad to find this Elecraft
> reflector!   David AC4BN
>