Dual LCD backlight inverter sensitive to backlight connections

[japlytic]

On a Mitsubishi AA084VC03 LCD (twin backlight) and a JX-02S210 V3.3 inverter module (the only two ICs were a common KA7500/TL494 PWM controller and a dual MOSFET for driving the transformer) for an LCD conversion of an oscilloscope, I had the problem of the backlight flashing on briefly then off in a loop with a bit of fizzing noise.
I tried reworking all of the solder joints (initially with the power connector) to no avail, even though the LCD module was well grounded .
Initially, I connected the LCD module with upper backlight connected to the backlight connector furtherest away from the transformer on the inverter module and the lower backlight connected to the backlight connector closest to the transformer; the backlight connector closest to the transformer only has one connection and therefore, this backlight has to rely on parasitic capacitance to illuminate.
When I connected the upper backlight furtherest away from the transformer and the lower backlight closest to the transformer, the backlight reliably illuminates .

Therefore, in theory, the VGA-LCD controller (Roward RTMC7C) could be sensing an overcurrent condition (+12V line with current sensing) with the backlight inverter; between the controller and the backlight inverter are three wires, Ground, +12V and Enable (+5V=ON).

So could some backlight inverters be sensitive to what backlight you connect to each backlight connector?

[budm]

Re: Dual LCD backlight inverter sensitive to backlight connections

"this backlight has to rely on parasitic capacitance to illuminate." I do not think so, the return wire from the lamp may be tied to the chassis some where that you are not seeing.
" fizzing noise." do you also smell Ozone? I t sounds like the bad connection to the lamp's end.
Any good clear pictures of what you are working on?

[stj]

Re: Dual LCD backlight inverter sensitive to backlight connections

if this is a conversion, why arent you using led's instead of tubes anyway?

i'm just starting a conversion myself.

satellite alignment meter.
going from a 4inch monochrome crt to a colour lcd with led backlight.
(it was dropped and the tube is internally fucked - incase your wondering)
one of these: