[Elecraft] KPA 100 - KIO2 not working...

[Don Wilhelm]

Rein,

I can find nothing in the circuit that could cause inverted signals on the
RS232 interface lines.  Be certain you have a negative voltage supplied to
U4 pin 8.  Ideally that voltage should be -12 volts, but anything between -5
and -25 volts should be OK.  If the voltage is not sufficiently negative, it
may cause the RS-232 lines to not swing far enough negative for proper
switching at the terminal device (computer serial port).

A logic low (ground ) on pin 12 of U4 should cause a negative voltage to be
presented on pin 5 - this is the binary one voltage for RS232 and can range
from -3 to -25 volts.
For a binary zero on the RS232 interface, the voltage should be positive +3
to +25 volts, and a +5 volt level on pin 12 of U4 should cause a positive
voltage to be present on U4 pin 5.  If this condition is what you have, the
signals are of the correct polarity.

The voltage doubler diodes D7 and D8 along with C35 and C38 are the 'power
supply' for the negative voltage while the oscillator Q8 and xtal X1 provide
the AC signal to the diodes.  Check these if the negative voltage is not
adequate.

73,
Don W3FPR

----- Original Message ----- 

>
> Of course I first did the mods on the control board... and I have checked
that
> the signals come through from the MCU to U4 on the KPA100. Only they are
> wrong!!. I have an RS232 tester, and I can see signals going from the
> terminal to the rig, and I can see the voltage swinging a bit on the input
> (MMU), but no reaction... as if the MCU is deaf. I have done everything
the
> manual said several times... Unfortunately I don't own an oscilloscope.
But
> the path from the terminal to the MMU looks o.k., it just doesn't work.
>
> The other way (TXD) it's different. When I compare the RS232 monitor
status
> with e.g. my OMNI VI, on the OMNI the LED is RED, on the K2 it's GREEN,
i.e.
> wrong polarity. Also no flicker of the LED or voltage change when I try to
> send the test message. And nothing on the terminal (works fine with the
OMNI,
> also at the same speed). And yes, of course I made a special cable for the
K2
> according to the manual. The firmware is 2.03d by the way...
>
> Rein PA0R
>
>