[Elecraft] K2 VCO frequency out of range and not changing

[Gareth - M5KVK]

Don,
Apologies for the slow response: I'm doing a lot of business travel right now.
Yes, you're right, I didn't provide much information. Sorry about that.

I managed to squeeze an hour in yesterday, and measured the voltages in the affected area. RF Board U4 is OK, except that CLK and DIN are both inverted. I hadn't noticed this when tracing with a scope. CLK (pin 7) is at 5.03V, whereas DIN (pin 5) is at 0V. They should be at the opposite ends.

Going to the Control Board confirms these readings on U7, but that's when I ran out of time. I did a visual inspection of U7 and it looks OK. I may get an hour this evening, so I'll check U6 and U8.

Gareth
> On 2 Jul 2014, at 16:33, Don Wilhelm <w3fpr at embarqmail.com> wrote:
> 
> Gareth,
> 
> You did not supply much information with frequencies and voltage measurements, so I have to guess a bit about what your problem may be.
> 
> Usually when the VCO frequency at TP1 does not change, you will also find that the VCO voltage measured at the left end of R30 is at one of its extreme voltages - either about 8 volts or about zero volts.
> 
> The solution is to either adjust L30 or adjust the turns on T5 (or both) to get the frequency of the VCO into a range where the PLL can adjust it.
> 
> The easiest way I can tell you which way to move the frequency at TP1 is to tell you to look at the VCO table on the Schematic Key page (the first page of the schematics near the back of the manual.
> Set the frequency on the VFO dial to the low end of a band (80 meters - 3500 kHz is good).
> Then measure the frequency at TP1 and compare it with the VFO frequency shown in the chart (for 80 meters it is 8415 kHz.
> If the frequency at TP1 is too high or too low, adjust the turns of T5 or adjust L30 to bring it onto frequency.  For gross adjustment, adjust the T5 turns spacing, and for fine adjustment use L30.
> Note - if the frequency at TP1 is WAAAAY off, you may have a problem with the capacitors or relays in the VFO Range Select area.  See the RF Board schematic sheet 1.  The Schematic Key VFO chart tells you the capacitors used for each band - check the value and soldering and check the soldering of relays K13, K14, and K15.
> 
> Once you have the right frequency when tuned to 3500 kHz, tune to 4000 kHz and measure the voltage at the left end of R30.  It should be able to be adjusted to something near 6 volts, and can then proceed to check the other bands as normal in the manual instructions.
> 
> 73,
> Don W3FPR