Posted by
Mike, W8ENG on
Nov 17, 2004; 12:44am
URL: http://elecraft.85.s1.nabble.com/Low-voltage-on-AGC-threshold-tp371652p371655.html
This is an update to my earlier post. I touched up a solder joint and
reassembled the radio. The voltage on pin 5 of U2 was still 3.78 volts,
with the RF gain set fully clockwise. The input voltage from my power
supply was 12.4 volts, both on my DMM and on the K2's internal voltmeter.
The voltage out on the 8v regulator was 7.8,a nd on the 5v regulator was
4.9.
I'm thinking that the problem may be low voltage all around. I don't have a
better power supply to check with at a higher voltage.
Any addational help or comments would be appreciated.
73, Mike, W8ENG
----- Original Message -----
From: "Mike, W8ENG" <
[hidden email]>
To: "W3FPR - Don Wilhelm" <
[hidden email]>; <
[hidden email]>
Sent: Monday, November 15, 2004 8:23 PM
Subject: Re: [Elecraft] Low voltage on AGC threshold
> Don, Thanks for the fast reply.
>
> I did have the FR gain fully CW during the test. Anyway, I just checked
> (for the third time) the solder joints on the control board. Pin 4 on RP6
> may have had a cold joint. I touched it up, and will re-assemble and
> recheck the votltage.
>
> 73
>
> Mike, W8EMG
>
> ----- Original Message -----
> From: "W3FPR - Don Wilhelm" <
[hidden email]>
> To: "Mike, W8ENG" <
[hidden email]>; <
[hidden email]>
> Sent: Monday, November 15, 2004 7:34 PM
> Subject: Re: [Elecraft] Low voltage on AGC threshold
>
>
> > Mike,
> >
> > Since your adjustment range is on the 'edge of the cliff', it would be a
> > good idea to identify what is causing it before it bites you later on.
> > Check all the components for proper values and check solder connections
> very
> > carefully to determine why you are running out of adjustment range.
Look
> at
> > the schematic to determine which components are connected to the AGC
> > threshold pot circuits and check them all with a careful eye, then check
> > again and when you have finished, check it once more - these things are
> > difficult to spot even with careful inspection (I know, I've been there,
> > done that many many times).
> >
> > 3.78 volts may be fine for the AGC Threshold adjustment - I often
> (usually)
> > find that the proper AGC threshold is between 3.6 and 3.8 volts.
> >
> > Just as an afterthought - you do have the RF gain control full clockwise
> do
> > you not? It will alter the reading on the AGC threshold measurement
> point.
> >
> > 73,
> > Don W3FPR
> >
> > ----- Original Message -----
> >
> > When setting the AGC threshold I was not able to get 3.8 volts on pin 5
of
> > U2 as described in the manual. The voltage varied from 2.60 to 3.78
when
> > adjusting R1 to the extreme settings. Is this close enough or should I
> have
> > more room for adjustment?
> >
> > I have a faily good DMM, and it compares very closely to the K2 internal
> > meter, and when checking values on 1% tolerance resisters. All other
> checks
> > to date have been fine.
> >
> >
> >
> >
>
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