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

[Ken Elhardt]

I'm getting private posts and forum posts and it's getting confusing.

To Bob Weigel, I had spent a lot of time going over the ribbon cable,
resoldering the connectors, pushing, pulling, bending PCB's, and none
of that would cause the display to go out, and none of it fixed the
problem either.  It was only after removing the backlight power that
the problem seemed to be solved, except of course I now have no
backlight.

To Scott Nordlund, Some of symptoms you mention like digital glitches
and a such also seemed to happen on rare occasions.  For instance
today when the display went out, it changed the patch number.
However, I'm not sure if getting a new LCD display will solve the
problem yet, because of the nonsense voltage or signal I'm getting
from the power supply board.  It's not currently DC which worries me.
There's AC there, but I can't measure because my scope will not
display a signal when there is a continuous spark on the probe tip.  I
noticed that when I moved the probe closer to the LCD PCB where the
power comes in, I started seeing some kind of AC signal on the scope,
even at a couple of inches away.  I suspect the boost converter or
whatever that is on the power supply board.  There is a high pitched
sound and noise that I can physically hear coming from there.  As per
my previous post, I temporarily disconnected the backlight and that
seemed to fix the problem, but since I wanted to put this keyboard up
for sale, having no backlight isn't preferable.  I'm just trying
confirm if it's a power supply problem so I don't waste time and money
buying a new LCD unit and not solve the problem.

Thanks,
-Elhardt