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

[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

[stj]

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

post lots of pictures, i have an idea.

[DrunkenMonk]

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

post lots of pictures, i have an idea.

Took two high-ish res photos, there's a couple of scratches into the solder mask on either side where the glue was removed, but upon checking they seem to be just the mask and I've got epoxy to tidy that up after I get the backlight working as intended.





And here's the backlight when it's turned on at full or low power

[stj]

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

oh shit!

firstly, look at your soldering - you have atleast 2 bridges.
second - wtf is going on with those cap sizes??
and you cant have them on long wires - that's inductive.

did you ever see the backlight working right btw?
because i suspect it may use a flourescent lamp like the gamegear and lynx - those wear out.

[DrunkenMonk]

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

oh shit!

firstly, look at your soldering - you have atleast 2 bridges.
second - wtf is going on with those cap sizes??
and you cant have them on long wires - that's inductive.

did you ever see the backlight working right btw?
because i suspect it may use a flourescent lamp like the gamegear and lynx - those wear out.

The cap sizes are just in place for testing purposes, they'll be replaced with the correct SMDs.
The lamp itself doesn't seem respond to voltage changes at all, so I don't think it's an issue with the the tube itself so much as the driving voltage, though I'll have to actively test that just to confirm, I'll get back to you on that one.

I'm not seeing the bridging you're referring to, you'd have to circle the areas you believe there to be bridges.

The long leads on the caps isn't an issue for this test case and they're specifically on the sound circuit which is running flawlessly

[stj]

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

bridges are not between cap pins, but between caps and other tracks
the gold one,
the 22uf c109 on the right,

[DrunkenMonk]

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

bridges are not between cap pins, but between caps and other tracks
the gold one,
the 22uf c109 on the right,

Double checked them, and I do see where you mean, but they're just close - I can take pictures from an angle and with the meter on continuity if you'd like to see?

But I can confirm they are not bridged, that is assuming you meant cc901 and cc704. The tiny bit that looks like it's sitting on top of the silkscreen is just a piece of debris on 901. 704 is just close to the via and not actually touching it.

Any other ideas?


*edit - actually I'm going to just use some common sense and try check the coils under t900 and t500 and see if they read right

[stj]

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

whats in the metal shields?
i dont see a transformer that could drive a tube.

[DrunkenMonk]

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

whats in the metal shields?
i dont see a transformer that could drive a tube.

Yeah the transformers are under the metal shields, I'll be removing them and testing them to see if they read back alright.

Q900 is the 24v transformer under the larger shield
Q500 I believe is 19v(?) for driving the LCD I'm not entirely positive on this one though. On the inverse of the board there's T900 and T901 which are also related to the backlight circuit, but I'm not sure what they're supposed to read

[stj]

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

on the top edge of the board is a teal (blue/green) film cap - it may be related to the tube drive.

[DrunkenMonk]

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

on the top edge of the board is a teal (blue/green) film cap - it may be related to the tube drive.

Yup it is, that BLH bridge is also able to be removed to disable the backlight entirely

[stj]

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

i wonder if that cap is still good to pass current.

[DrunkenMonk]

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

i wonder if that cap is still good to pass current.

I can remove it and check? But I'm not too sure what it's rating should be

[DrunkenMonk]

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

Okay I eventually got around to checking, and the larger transformer T900's primary isn't open, but the smaller T500 transformer seems to be testing okay - so I think I'll try find a replacement for T900 at this point or failing that, just replace the LCD with a modern backlit system where I can just tap 5v somewhere for the backlight.


*edit:
game gear transformer seems perfect for it and I've got a few lying around, huzzah ��

[stj]

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

if your adventurous, maybe you could swap the tube out for a tiny led strip.
like in the fake "filament" lamp bulbs.

does the console run o.k. other than the light?

[DrunkenMonk]

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

if your adventurous, maybe you could swap the tube out for a tiny led strip.
like in the fake "filament" lamp bulbs.

does the console run o.k. other than the light?

Can't tell with the backlight being so dim, but I can at least hear the sound and hear button presses and etc in games playing the sounds I'd expect to hear, one problem at a time since I know the ram is another point of failure on these suckers aha, if it does end up working I'll clean it all up, put on the rest of the smd caps and leave it stock for now opposed to replacing the ccfl since that way it's still oem looking from the outside.

Will update tomorrow(later today when I wake up) if replacing the transformer works though, still not sure if q500 and q900 are okay, the transformer might've taken q900 out with it too

[DrunkenMonk]

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

Looks like a solid NO on replacing the transformer, same issue with the backlight being low brightness and the wheel seemingly not changing the brightness any. So I know the transformer is good since I took it from a game gear that it was working fine to drive the ccfl.
I'll swap over that little green film cap too, but I doubt that'll affect anything. It's probably got to be Q500 or Q900, I'll have to get some readings from them to verify they're actually outputting something...

I don't really want to just give up and swap the screen with an LCD aha, but it looks like that's definitely on the cards. The primary is open on this replaced transformer though, so it definitely does seem like something went awry around this area and something probably burnt out...

[stj]

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

i really think you should see the image on the lcd!
maybe the problem is upstream and some power rail is low.

[DrunkenMonk]

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

i really think you should see the image on the lcd!
maybe the problem is upstream and some power rail is low.

I'm pretty sure it's just incredibly dark, but I do have a potential donor pc engine for a video chip if that does end up being a problem too, I've attempted to shine a light at it to see if i I can see anything displaying but the polarization seems a little too strong for the dainty little light from my phone camera aha. I might try hook up a composite LCD without fully modifying the system to get the skinny and see if there's a different story to be told

[stj]

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

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!