Serial Port on K3

[N4CW]

Jim, K9YC,
 
Let me address the questions you posed in your e-mail:
 
1. The K3 was powered directly from a 54-AH AGM battery using a  4-foot #10
red/black wire pair (same as
what I use in the shack with an Astron RS-35M).
2. The computer/laptop (IBM Thinkpad 390X -- with genuine RS232 serial  
port) is powered by a mobile
power supply specifically designed for the Thinkpads by IBM).
3. RF is not the issue here...the failure is obvious in receive mode...no  
rig control as manifested by no
frequency display/readout in N1MM Logger. So the antenna (an Outbacker  
Outreach with a 4-foot Hustler
mast extension on the base to resonate the antenna in the CW portion of the
 band -- measured with an
MFJ-259B).
4. The serial cable is the same cable I use in the shack. A non-issue since
 I tried another cable.
 
The point I tried to make is that IN THE CAR, I substituted an AC supply  
(AC thru75-Watt inverter/converter plugged into an Astron SS-30 power supply  
that produces 13.8 VDC -- receive mode on the K3 because of
power limitations) for the battery (unplug one, plug in the other, leaving  
all other cables attached) and the
laptop now communicated with the K3 (manifested by the proper frequency  
being displayed by N1MM Logger). The only thing that changed was the power  
source.
 
 Ordinarily, I never power my K3 from other that more-than-adequate  
13.8-Volt DC supplies, but this was like an emergency/field day setup and it  
disclosed a problem. Now, you see my concern about the K3 serial port failing  
with a lowered supply voltage to the K3?
 
Thanks for your other suggestions.
 
Bert, N4CW
 
 
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[Guido Tedeschi-2]

2012/2/29 <[hidden email]>

>  Ordinarily, I never power my K3 from other that more-than-adequate
> 13.8-Volt DC supplies, but this was like an emergency/field day setup and
> it
> disclosed a problem. Now, you see my concern about the K3 serial port
> failing
> with a lowered supply voltage to the K3?
>
>
Hi Bert,
   some time ago, the K3 of a friend had a problem on KIO3, with the RS232
that stopped
working if the power supply voltage was lower than 13V.
I found that the problem was the lacking of negative voltage on pin8 of U1
(LT1039ACN) and a few measurements, with a scope, shown that the 1KHz
oscillator made with Q1 did not oscillates at all with less than 13V.
Looking at oscillator components, nothing seems damaged
neither"cold-soldered" and the junctions of Q1 were fine...
 The "Elecraft Super Customer Service" sent very quickly to us a new KIO3
board and, after the substitution, all went fine.
Then, for fun, I troubleshooted the faulty KIO3.
If I remember well, I had to increase the R1 resistor value from 1K to
2.2K, 3.3K or 4.7K (sorry, I don't remember the value and the board is at
friend's home as spare part...).
After that modification, the negative voltage generator on KIO3 worked fine
even with only 10V...
73 de Guido, ik2bcp
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