TurboExpress - looking for schematic to diagnose low power to backlight/lcd

[DrunkenMonk]

Originally Posted by stj

if you can slide out the tube, you could poke a white led into the hole in the reflector

it will be funny if it turns out to be a contrast control problem!

Okay so after I did some digging around for expected voltages in certain locations I came across VR501 which is functioning perfectly fine as a potentiometer however it's only receiving 2.8v and outputting 0.2v when it's expected output according to console5 is actually 4.5v. So I do have a voltage drop somewhere...
I've ordered some replacements for Q500, Q900 and Q901 since I know they're all related to the backlight circuit just to rule them all out, I'm thinking Q500 is probably what is supposed to drive the power for VR501, so hopefully just replacing that fixes something else

[Alterac]

If you are still having issues give this a try:

A good thing to do would be remove Q900/Q901, and Q500,Q501, D502,D503 clean under them, and the components themselves, and resolder them back on, as the electrolytic juice is conductive enough to distrupt things. (wouldnt hurt with D9xx either)

Also, try for the following voltages at these Test points:
TP500 30v
TP501 -24v
TP502 5v (ish, you will see it from 4.8 to 5v depending on factory)

The 2x Variable Resistors adjust the supply rails:
VR500 LCD Voltage Adjust (-24v)
VR501 System 5v Adjust

The 900 series of components is for the Highvoltage CCFL Backlight circuit, and the 500 series does the -24v for the LCD Panel, along with other system voltages, 30v, 5v, etc.
1xx is Audio, 2xx is for LCD Datalines/connector area

[mario_pic]

Originally Posted by DrunkenMonk

So as per the title, I've got a turboexpress here that was recapped with nichicon caps, the fuse and one of the coils was replaced (possibly popped due to an over-voltage or negative voltage?) and the audio is now great but the backlight doesn't show a bright vibrant white like it should, and doesn't look like it adjusts at all using the wheel, but after checking the wheel it looks like it's reading fine, so I can only assume I'm not getting the correct voltage somewhere... FUN

So I'm not sure if it's part of the coil circuit or one of the regulators since I don't know what they should be outputting or where the backlight circuit is in it's entirety.

If anybody has some schematics, ideas or even just some chickenscratch notes I'd be very appreciative

iv fixed quite a few of these consoles and done few lcd mods one thing i find leaky caps eat threw hole traces one trick os use a blacklight to find stains from acid bet can find broken trace also the turbo express is just a portable version of the pc engine console all thsy did was intagrate an tft lcd