[Elecraft] KAT100 signal question

[W3FPR - Don Wilhelm]

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.

73,
Don W3FPR

> -----Original Message-----
>
> In troubleshooting a relay problem on my KAT100, Gary advised me
> to check the
> signal /8R, generated by Q3.   I think Q3 may be faulty, since
> (using a Fluke
> DMM) signal /8R alternates between zero and only 4.99v as the KPA100 is
> cycled between receive and TUNE.   Signal 8R alternates between
> 7.91v and zero, as
> I would expect.
>
> Before, I disassemble, de-solder, and install a new Q3, however, could
> someone verify that 4.99 v is indeed lower than it should be and
> Q3 is probably bad.
>   Thanks.
>
>
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