[Elecraft] K3 Won't Turn On all of a sudden!

[Michael Carter]

Hi Rick,

I've not experienced the problem you described,
but I've also not used my K3 as a remote front panel
for another K3.

Have you checked pin 8 of the ACC connector to
be sure that it is not held 'high' by some chance
(not likely since you pulled all the cables)?

If there isn't a problem with that ACC pin and
accompanying circuit in the KIO3 digital interface,
I would investigate Q2, the 2N7002K MOSFET
on the front panel board.

Once the POWER switch is depressed, that pulls
up the gate voltage of Q3, thus pulling down
the /PWRON signal, which is required to be
held low to keep the series-connected P-MOSFET
in the 12 VDC input line conducting for the switched
power supplied to the rest of the radio.  That /PWRON
line is held low if Q2 receives the POWERHOLDON
signal from the front panel MCU even after the
front panel POWER switch is released.

The LCD display backlight is powered from
the 8V regulator when a signal VLCDBKLT
from the MCU is asserted.  The LCD segment drives come
from a separate controller chip rather than
the MCU directly.  I'll hazard a guess that your
MCU is operating properly, but something in the
POWERHOLDON path is not allowing Q2's gate to
be held high, thus turning off the K3 when the
POWER switch is released.

Mike, K8CN