[Elecraft] Serial Port on K3

[Guido Tedeschi]

2012/2/29 <N4CW at aol.com>

>  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