[Elecraft] P3 Misbehaving?

[Sanger, Joseph]

The noise floor shifts by 10 db each time I make a change to the PRE or ATT switch ... resulting in 3 separate noise floor levels.  But you are right, the RF board turned out to be the problem!  You will see on my next post, the final chapter.

Thanks very much, Bob.

-----Original Message-----
From: Bob Cunnings [mailto:bob.cunnings at gmail.com] 
Sent: Saturday, September 11, 2010 8:10 PM
To: Sanger, Joseph
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] P3 Misbehaving?

Is the noise floor on the P3 stuck at -140 dBm or so all the time, no
matter what?  I experienced a similar problem after 2 weeks of use,
and replacement of the P3 RF board was required. Apparently, I was
informed, another cause can be handling damage to transformers T100 or
T101 on the P3 Front Panel board, so you might take a look at them.  I
sure wish the P3 schematic was available at the time, it would have
made troubleshooting a little easier (it's still not published
AFAICS). As usual, Elecraft support was prompt and efficient, I'd
contact them if there's no change.

Bob NW8L

On Sat, Sep 11, 2010 at 4:34 PM, Sanger, Joseph <Joseph.Sanger at nyumc.org> wrote:
> Just assembled P3 a few days ago.  Having a problem that I can't seem to solve.
>
> Background:  Haven't done K3 OUT mod yet (SN 113 ---- fairly old) ... really am apprehensive about opening up K3 again ... but I know I'm just being neurotic ... will face any weekend now).
>
> The P3 was pretty much performing as expected ... given that I haven't done the above mode yet, and I live in manhattan with a mediocre hamstick hung outside my window .. I could generally see strongest stations above a lot of noise on P3.  That was good.
>
> But over past few days, it seems that the sensitivity of the device was diminishing .. started to have trouble seeing the few stations that I could actually hear above the noise on my K3 ... and then today, it now appears that the P3 is basically deaf to the K3 ... I see some low ampitude noise, which doesn't vary in appearance with or without the coax cable to the IF OUT of the K3 plugged in.  I am listening to a fairly strong Italian CW station now on 20 meters now, sticking his head above the omnipresent S5-6 noise ... armchair copy, if you will, but all I see is noise at the bottom of the P3 screen.  The center frequency tracks my K3 nicely ... but no matter how I adjust the REF, SCALE and SPAN, all I see is noise.
>
> Any thoughts would be welcome.  Yes, I will dive in and do the IF OUT mod, but am trying to understand the curious behavior, and to see if it sounds familiar to anyone.
>
> Thanks in advance
>
> -- WB2SSB
>
> Joseph J. Sanger, M.D.
> Associate Professor of Radiology
> Director, Radiology Informatics

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