K2: Low 8V, and adjusting AGC and S-meter

[TF3KX]

Hi:

My K2 #6425 was ordered in February and is now fully operational, with almost all measurements and checks within limits.  The only issue is the output of the 8V regulator, which is at 7.56V (5.5% down from the nominal 8V).  If I am right, this low voltage is the cause for...

a)  AGC threshold adjustment:  U2 pin 5 voltage only goes up to 3.62V, not 3.80V;
b)  S-meter adjustment:  Can never get S-meter LED below #2 or above #9 to turn on.

I had to order some spare parts from Elecraft, and to be safe I asked them also to send me a tested replacement for the 8V regulator - which is on the way.

My questions are...
- Wouldn't the low 8V level be the cause of the above symptoms (a) and (b)?
- Any reason I should or should not replace that 8V regulator, anyway?

73 - Kristinn, TF3KX

[DW Holtman]

Kristinn,

I had the exact same problem. I replaced the regulator with one that
operates at 8.0 VDC and the AGC adjusted correctly. I don't know if they
received a batch of bad chips, but I used one that I had on hand, not one
from Elecraft.

Good luck.

Best,
DW Holtman
WB7SSN

----- Original Message -----
From: "TF3KX" <[hidden email]>
To: <[hidden email]>
Sent: Sunday, May 11, 2008 6:25 PM
Subject: [Elecraft] K2: Low 8V, and adjusting AGC and S-meter

>
> Hi:
>
> My K2 #6425 was ordered in February and is now fully operational, with
> almost all measurements and checks within limits.  The only issue is the
> output of the 8V regulator, which is at 7.56V (5.5% down from the nominal
> 8V).  If I am right, this low voltage is the cause for...
>
> a)  AGC threshold adjustment:  U2 pin 5 voltage only goes up to 3.62V, not
> 3.80V;
> b)  S-meter adjustment:  Can never get S-meter LED below #2 or above #9 to
> turn on.
>
> I had to order some spare parts from Elecraft, and to be safe I asked them
> also to send me a tested replacement for the 8V regulator - which is on
> the
> way.
>
> My questions are...
> - Wouldn't the low 8V level be the cause of the above symptoms (a) and
> (b)?
> - Any reason I should or should not replace that 8V regulator, anyway?
>
> 73 - Kristinn, TF3KX
> --
> View this message in context:
> http://www.nabble.com/K2%3A-Low-8V%2C-and-adjusting-AGC-and-S-meter-tp17179721p17179721.html
> Sent from the Elecraft mailing list archive at Nabble.com.
>
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[Dave Andrus-3]

Kristinn:

In answer to a):

Yes, that is correct.  Several of us that have built K2's in recent  
times have found that the 8V regulator output is low by as much as 0.5  
volts.  Replacing it should give you a good chance of seeing higher  
voltage, and being able to adjust the AGC threshold to 3.8V.  My  
regulator output was 7.51 volts, if I recall correctly, and Elecraft  
sent me a new one.  Interestingly, I looked up the manufacturer's data  
sheet for this part, and it is very near, but still within the  
manufacturer's tolerance.

I believe that this should also fix b), but I did not experience this  
with my unit.

73,

Dave K7DAA
http://www.k7daa.com

On May 11, 2008, at 5:25 PM, TF3KX wrote:

>
> Hi:
>
> My K2 #6425 was ordered in February and is now fully operational, with
> almost all measurements and checks within limits.  The only issue is  
> the
> output of the 8V regulator, which is at 7.56V (5.5% down from the  
> nominal
> 8V).  If I am right, this low voltage is the cause for...
>
> a)  AGC threshold adjustment:  U2 pin 5 voltage only goes up to  
> 3.62V, not
> 3.80V;
> b)  S-meter adjustment:  Can never get S-meter LED below #2 or above  
> #9 to
> turn on.
>
> I had to order some spare parts from Elecraft, and to be safe I  
> asked them
> also to send me a tested replacement for the 8V regulator - which is  
> on the
> way.
>
> My questions are...
> - Wouldn't the low 8V level be the cause of the above symptoms (a)  
> and (b)?
> - Any reason I should or should not replace that 8V regulator, anyway?
>
> 73 - Kristinn, TF3KX
> --
> View this message in context: http://www.nabble.com/K2%3A-Low-8V%2C-and-adjusting-AGC-and-S-meter-tp17179721p17179721.html
> Sent from the Elecraft mailing list archive at Nabble.com.
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com

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