[Elecraft] K2.Unable to undertake VCO alignment.

[Don Wilhelm]

What were the results of the PLL Reference Oscillator test - especially 
the high frequency at TP3? - the frequencies please.

The 5 volts on the SCK signal is normal.

Do not wear out the slug in L30!

Is this a new build or the result of upgrades to an old K2?
Do you have an oscilloscope with a 10X probe?

73,
Don W3FPR

On 1/27/2021 6:59 AM, M Bak wrote:
> Issue. Unable to undertake VCO alignment. Voltage at R30 fixed at 24mV.
> 
> 
> 
> The VCO oscillator test (Alignment and test Part II p 63) has passed. Well
> the frequency is 7.98MHz rather than 8->10 but that conceivably could be
> within the bounds of measurement error.
> 
> 
> 
> In the VCO alignment test a DMM (Keysight U1271) clamped onto the left side
> end of R30 reads 24mV no matter what the setting of L30.
> 
> 
> 
> I have looked everywhere over the appropriate circuitry but can see no
> issues. Including triple checking T5 which is 100% wound and fitted
> properly.
> 
> 
> 
> I made the measurements from troubleshooting (PLL Reference Oscillator and
> VCO P 10) and got:-
> 
> 
> 
> Reference Oscillator Output  0.72
> 
> VCO Output 0.24
> 
> VCO Buffer Output 0.59
> 
> All measurements are at the low end of the acceptable range but just in
> spec.
> 
> 
> 
> 
> 
> I measured voltages in the area and have noted the following:-
> 
> 
> 
> 1.     U4 (MC145170) pin 7 CLK/SCK is at 5v as against the specified 0v.
> 
> 2.     U4 pin 13 PDOUT is at 5v rather than 4v. This feeds the inverting
> input of U6B causing the output to be low.
> 
> 3.     The gate input of Q18 is 0 rather than -1.
> 
> 
> 
> 
> 
> I am at a loss as to what to check next and any suggestions would be most
> welcome. BTW I also have a ½ decent scope so can probe with that assuming I
> can figure out what I should be seeing. The K2 is a brilliant kit but
> seriously different to tube amps. which is my usual playpen.
> 
> 
> Thanks
>