[Elecraft] Elecraft K2 7855, alignment and test part II, bad PLL frequency.

[Don Wilhelm]

Chris,

Your English is much better than my French!  I hope you can understand 
the following:

You have a Q19 that is not willing to work at the high frequency end of 
the PLL range.

The proper thing to do is replace Q19 with a J310 FET that is better. 
Order one from Elecraft (email to support at elecraft.com) with the part 
number.

What you can try is to add a small value capacitor (12 or 15pF) from U4 
pin 1 to U4 pin 12 (ground) to see if that restores proper function.  If 
you do not have a stock of small capacitors, use the 12pF in the K2 kit 
which you have not yet installed and order a replacement from Elecraft.

Proper functioning thru-hole J310s have been a problem since Elecraft 
ran out of the old ones and found that they had been discontinued by the 
manufacturer.

I know of one ham in Europe who used an SMD J310 as a replacement - but 
if you consider that, know that the basing is not the same and you would 
have to go from the data sheet to know which pin to connect to the 
holes.  He mounted it on the bottom of the board.

73,
Don W3FPR

On 5/6/2020 4:44 PM, Christophe GIBERT wrote:
> Hi! First of all, sorry for my poor english, i’m french ;-)
> 
> I’m building my k2 number 7855.
> 
> In the first step of the 4mhz oscillator calibration, i get a frequency of 00500.00 instead of 12090.00
> 
> When i press BAND + : 00475.00 and BAND - : 12085.43 (stable).
> 
> I’ve tested probe on TP2, I’d 4913.52
> 
> I reviewed all components in the pll schematics and nothing seems wrong.
> 
> Please help me, i don’t know what to look for now.
> 
> Thanks a lot.
> 
> —
> Chris
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