"mikem" wrote in message
ups.com...
Unearth the aircraft battery, look to see if there are any connections
to the positive pole upstream from the master relay. You might find
one: the clock keep-alive circuit which should have a 1A cartridge
fuse in series with it. If there are any other connections upstream of
the master relay, you need to trace them to see where they go.

I believe the certification regs allow up to a 5 amp breaker/fuse directly
from the battery for "keep alive".



With the master off, it is
unpowered, and it would not matter if headsets were plugged in or not.
It supplies the mic current to the backseat headsets, so if it is off,
they are off too. Sounds like some dumb**** who didn't have a clue
installed the intercom!

Amen to the dumb**** comment. The easy way to tell if this is a ds problem
is to get an aircraft mic plug (0.206" diameter) into the back seat mic
jack(s) and see if there is voltage with respect to airframe ground on
either of the two hot leads (ring or tip) with the master switch off. If
there is voltage present, read the paragraph above, especially the last
sentence. While I cannot conceive of voltage being on the aircraft phones
plug, just to satisfy the curious, do the same test on the hot lead of a
phones plug (0.250" diameter) plugged into the back seat jack(s)



A common problem with older electrically-powered self-winding aircraft
clocks is that the winding solenoid intermitently sticks on, which will
run down your battery is short order.
As the clock spring runs down, a switch closes, applying power to a
solenoid, which is supposed to "wind UP" the spring, causing the switch
contact to open again. If the switch stays on, the solenoid remains
powered... Best fix is to chuck the mechanical clock and replace it
with a LCD pure electronic version...

Many of the Target/K-Mart "travel alarm clocks" can be gutted and installed
into an old mechanical clock housing. They run from a single AA cell that
can be clipped to the back of the case. Change the battery every annual and
you don't have to have a keep-alive breaker/fuse installed at all.

Jim