Re: TurboExpress - looking for schematic to diagnose low power to backlight/lcd
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...
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Re: TurboExpress - looking for schematic to diagnose low power to backlight/lcd
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...Last edited by DrunkenMonk; 02-03-2021, 10:16 PM.
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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...
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Re: TurboExpress - looking for schematic to diagnose low power to backlight/lcd
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...Last edited by DrunkenMonk; 02-02-2021, 10:16 PM.
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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, huzzahLast edited by DrunkenMonk; 02-02-2021, 04:21 PM.
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Re: TurboExpress - looking for schematic to diagnose low power to backlight/lcd
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...
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Re: TurboExpress - looking for schematic to diagnose low power to backlight/lcd
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...Last edited by DrunkenMonk; 01-31-2021, 12:01 PM.
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Re: TurboExpress - looking for schematic to diagnose low power to backlight/lcd
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.
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Re: TurboExpress - looking for schematic to diagnose low power to backlight/lcd
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
...Last edited by DrunkenMonk; 01-30-2021, 01:06 PM.
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TurboExpress - looking for schematic to diagnose low power to backlight/lcd
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...
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