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

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Christophe GIBERT

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

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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Don Wilhelm

Re: Elecraft K2 7855, alignment and test part II, bad PLL frequency.

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 [hidden email]) 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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Christophe GIBERT

Re: Elecraft K2 7855, alignment and test part II, bad PLL frequency.

Hey ! I’ve soldered a 20pF capacitor that i’d from personal stock between U4 pin 1 and U4 pin 12 (ground), and all is good !

I can go to BFO Test without any problem !

Does this mod could be considered as definitive or should I change Q19 with another J310 ?

Thanks a lot for the super hyper quick help! :-)

Best regards.

—
Chris

> Le 6 mai 2020 à 23:37, Don Wilhelm <[hidden email]> a écrit :
>
> 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 [hidden email]) 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
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]

Don Wilhelm

Re: Elecraft K2 7855, alignment and test part II, bad PLL frequency.

Chris,

Congratulations. Leave the capacitor in and go on. On other words,
treat it as a permanent fix - you might also want to add it to your
schematic.
No need to change Q19.

73,
Don W3FPR

On 5/7/2020 12:25 PM, Christophe GIBERT wrote:

> Hey ! I’ve soldered a 20pF capacitor that i’d from personal stock between U4 pin 1 and U4 pin 12 (ground), and all is good !
>
> I can go to BFO Test without any problem !
>
> Does this mod could be considered as definitive or should I change Q19 with another J310 ?
>
> Thanks a lot for the super hyper quick help! :-)
>
> Best regards.
>
> —
> Chris
>
>> Le 6 mai 2020 à 23:37, Don Wilhelm <[hidden email]> a écrit :
>>
>> 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 [hidden email]) 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
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to [hidden email]