Re[2]: [Icom] a little r7000 whine ..

John Blue [email protected]
Fri, 15 Nov 2002 17:16:09 -0600


CWW> I'd fix the meter lamp first.  You may find that something other
CWW> than the bulb or whatever is failed.  I would expect the whine to
CWW> be coming from a DC-DC converter which is jumping into a strange
CWW> mode.  But even if it is, something had to vibrate enough to make
CWW> a sound.  Does the whine come from the speaker?  If not, search
CWW> for the component, (a transformer or iron core coil) that is the
CWW> source.  That's only the first step.         73   Clete


I follow ya on that one Clete.  Well once I cracked the case .. the
meter lamp decided to start working.  heh, go figure.

I cannot tell if it is coming from the LCD or a can xfmr on the
display board.  I can tell you that the expected voltages for dimming
the display are not correct, and this is where it gets weird.

The display DIM switch looks to be just a SPDT open/close switch for
power that is center tapped off of a can xfmr on the display board.
It gets ran through a cap, in parallel with two zeners and fed back
into a full wave off of the same can.  Thats it.  I dont understand
how that is suppose to work but the schematic say that when the DIM
switch is off I should have -30.0 VDC and -9.0 VDC when on.

I read -26.3 VDC off and -28.3 VDC when on.  All other TP's check out
fine and the display dim's as it is suppose to.

A fellow avionics instructor who also works out at American said that
they replace LCD displays regularly but usually they are discolored on
one end, this one is not, yet.  He suggested that I shotgun it and
start with the xfmr first.
 
I know I am probably fishing by now .. but I wanted to bounce it off
you hardcore icom radio techs to see what ya thought.  :)

John Blue