Greetings.
A couple of years ago, while working a contest, I realized my K2 seemed a
little deaf. I run the radio using its internal batteries. I was calling CQ
and got no response. To save batteries on the K2, I turned it off and turned
on my Grundig Satellite 800 shortwave located near by. Using the Grundig, I
was surprised to hear a station calling me. Switch back to the K2 I found I
couldn't hear the station I heard on the Grundig. The Grundig was using only a
built-in whip antenna and the K2 was connected to a Superantennas MP-1 antenna
located just a few feet away.
I acquired this radio from the original builder 6 months after it was
assembled. I may not have built this unit but I have spent a lot of time going
through its guts and applying mods. I have applied all but the last two of the
la3za listed mods to bring my K2 #2172 in line with the 3000+ K2's. The mods
include the A/B kit update, and the PLL stability mod.
I have downloaded updated versions of some of the pages I had printed out
previously. Namely, the LA3ZA page with mod info for the K2, the Spectogram
alignment procedure. I also downloaded the latest copy of the Rev. G manual
(to compare against my Rev. C), and the one for the KSB2. I have temporarily
removed the KSB2 from my unit until I feel the base unit is working as
expected. I also have a printout of Gary's message fom 2000 titled "K2: 25
reasons for low RX sensitivity or low audio".
My sudden push to try and identify, and hopefully fix, problems with my K2 is
due to my having temporary use of a 20MHz handheld oscilloscope. The scope is
on loan from a client while I'm working on a project. I won't be able to hang
on to the scope much longer. I've been going back over messages I kept when I
was originally on this list back in 2002, plus some more recent messages.
I find I am usually running the K2 with the pre-amp on. When listening to a
station on the K2 I have the volume control set to around the 9 or 10 o'clock
position so I don't feel there is a problem with the audio amp.
My 8V regulator measures 8.45V on its output. I replaced R1 on the control
board with a 5k8 resistor in series with a 20k multi-turn trim-pot. I have
tried AGC voltages from about 3.6 up to 4.1 and still have a noticeable
difference in noise level when turning the AGC on and off. I curently have the
AGC voltage set to 4.1V.
A message I had kept from 2002 said to check for between 2.2 and 2.4V on TP1
on 160. I went to 80m (my lowest band) and measured about 2.2V. I removed T5
from the board as I didn't like the spacing of the turns around it. I
discovered two turns of the secondary were side by side. I removed the
secondary, adjusted the spacing of the primary to be more even, and rewound
the secondary (positioning it so its first turn was between turns 6 and 7 of
the primary instead of between 7 and 8). After re-installing T5, I had 2.5V at
TP1.
After having altered T5 I went back and check the VCO control voltage at the
left-side of R30 and read only 5.26V (at 4MHz). I adjusted L30 until I read 6V
and verified all the other VCO control voltages are within range. The lowest
reading is 1.99V and highest is 6V.
The last time I adjusted the bandpass filters I used the updated information
that says to use a max. transmit power of 1W. I haven't re-checked these
filters but they should be ok. The simple N0SS signal tracing method on 40m
didn't show much of a problem when I used myself as an antenna while holding
on to one lead of a 22 nF cap.
My main issues at the moment are:
1. What voltage should I be getting at TP1 when tuned to 80m?
2. What other things should I be checking in the AGC circuit that could
account for hearing a change in signal between AGC on/off regardless of how I
set the trim-pot adjustment?
3. Are there some key RF voltage readings I should take to verify all is well
while I still have access to a scope?
--
Cheers!
Kevin.
http://www.ve3syb.ca/ |"What are we going to do today, Borg?"
Owner of Elecraft K2 #2172 |"Same thing we always do, Pinkutus:
| Try to assimilate the world!"
#include <disclaimer/favourite> | -Pinkutus & the Borg
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