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

[GRAHAM ATKINS]

Ken,

The PPG Wave synthesizers used a high voltage inverter. Have a look at  
the
Virtual Music site :-

http://www.virtual-music.at/webseiten_e/zubehoer/ppg.htm#wavebl

Graham

On Sep 24, 2008, at 2:41, Ken Elhardt wrote:

> 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
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