Posted by
Geoffrey Mackenzie-Kennedy-2 on
May 21, 2006; 2:50pm
URL: http://elecraft.85.s1.nabble.com/K2-AGC-Off-Problem-tp389830p389835.html
If in some cases the value of C8 has to be reduced OR the value of C7 has to
be increased ( as Wayne suggests ) for proper operation of the 5.068 MHz
oscillator, it would seem that the original capacitor values result in too
much feedback in the oscillator. This could be a "batch" problem where some
crystals have a higher Q than the norm OR the oscillator part of the NE602
(U1) has higher gain than the norm, or both. IMHO changing the value of
either C8 or C7 sounds like a good fix, and any small change in frequency
that results does not matter.
If it is a "batch" problem I would think that it would affect a small group
of K2s (by serial number) if Elecraft use the crystals / NE602s soon after
delivery. Whether or not the problem deserves a Builder Alert should be
suggested by a more experienced "Elecrafter" than I.
73,
Geoff
GM4ESD
----- Original Message -----
From: "Nick Waterman" <
[hidden email]>
To: <
[hidden email]>; <
[hidden email]>
Cc: <
[hidden email]>
Sent: Sunday, May 21, 2006 9:36 AM
Subject: Re: [Elecraft] K2 AGC Off Problem
>> Thanks for the message.
>> A 10 pf at C8 did the trick. The receiver is now working properly in AGC
>> off
>> mode.
>
> Think that's at least 5 or 6 of us on the reflector have had this issue,
> and this easy fix, so far. Does it deserve a builder alert on the
> website yet?
>
> For anyone else: If you are seeing AGC problems (hold PRE/ATT and AGC,
> see if your K2 goes deaf), check your junk box for a 10pF cap and change
> control board C8. Wayne says 680 pF at C7 may be another option. I DO
> NOT recommend this mod UNLESS you're seeing "AGC OFF" issues though.
>
> --
> "Nosey" Nick Waterman, G7RZQ, K2 #5209.
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