[Elecraft] KAT100 signal question

[BobConvers at aol.com]

Jack, as I mentioned to Don, I get NO relay action on ANY relay, as I switch 
from ANT1 to ANT2 and /or adjust POWER on the K2/KPA100.   The KAT100 front 
panel LEDs light up correctly.

I was almost certain that before when I checked I saw no change on RYDATA, 
but I checked again and found that RYDATA does indeed switch from steady 5v to 
steady zero and back, when I switch from ANT1 to ANT2 and back.   POWER adjust 
has no effect on RYDATA.   FPDATA is at 5v for for all positions of the K2 
panel, although FPDATA briefly drops and returns to 5v when I adjust the K2 and 
the KAT100 LEDs switch.

>>>>>
 Q3 is probably not your problem. It is an open-drain switch that 
inverts the 8R signal, conditioning it for the microcontroller. It 
appears that the MCU provides the pullup for the signal through the 
internal pullup on PB6. 4.99 volts is about right for this signal.

Just what is the "relay problem" you are seeing? If Q3 and the /8R 
signals were bad, the KAT would not switch to transmit conditions at 
all. This would be indicated in a number of ways, such as not even 
trying to tune. Relay troubles, however, could be isolated to a small 
area in the circuit.