[sdiy] Bizarre LCD Display Behavior & Is backlight AC or DC Voltage?

[Ken Elhardt]

I have a Kawai K5000S Additive Synthesis Synth that works fine except
for a flakey LCD display (typical approximately 5" x 2" display).
Randomly the text will just go out, and it only comes back after a
power cycle.  It might work for only 3 seconds, or it might last days
and work fine.  After much probing and trouble shooting, it appears
the power to the backlight (which never goes out) is causing the
problem.  I was feeling a mild AC voltage on part of the LCD board and
also on a very small, about less than 1", transformer on the power
supply, which seems to power the backlight.  When I touch an O-scope
probe to the voltage powering the backlight, the text goes out, the
backlight flickers, and I also get noise on the audio outputs (it
doesn't like that).  Plus I noticed a continual small spark between my
probe and point of contact.  Does anybody know whether the backlights
are powered by an AC or DC voltage in these types of displays?  And is
there ever a normal situation when a signal can't be probed and looked
at on a scope and emits a continuous spark between probe and point of
contact?

BTW, I've had the unit running for hours with the backlight unplugged,
and text/graphics haven't gone out.  So I need to do something about
this strange backlight problem.

-Elhardt