[Elecraft] KAT100 signal question

[BobConvers at aol.com]

Thanks, Don.   Actually, I get NO action from ANY relay, although the LEDs 
are switching correctly.   I tried to check the signal RYDATA (as best I could 
with no scope, only DMM) and it is an absolutely constant level.   The front 
panel signal FPDATA jumps around in value as the signals come through to 
activate the LEDs, but RYDATA is dead still.   There is 12 v on the the hot side of 
the relays and 5 volts on pins 2 of U2, U3, and U4.   With power removed, 
RYDATA measures over 5 megs to ground.   Any other suggestions?   

73,
Bob, WO3E


>>>>
 Bob,

I would think Q3 is OK since it simply acts as a switch - it does not
produce any voltage.  The MCU (U1) pin 39 is the source for voltage on the
drain of Q3, and a high level of somewhere near 5 volts is to be expected.

Look somewhere else for the problem.  It is difficult to see directly
whether the microprocessor is creating the correct output because it is fed
to the relay drivers as serial data, but the relay driver pins should have
the outputs for the selected relays at a low level, and go to about 12 volts
on the pins connected to the unselected relays.  Check the schematic sheet 1
to see which pins correspond to which relays.