TG - Issue related RAM or video chip?

[DrunkenMonk]

So I've got this Turbo Express with a bad backlight circuit (not really a problem, I can figure that out) and was going to swap the screen over on it anyway to a 3.5" (I wired up a composite screen for easier, open air testing, but it also has weird graphical issues that appear to plague gameplay, which makes me figure it's maybe bad ram or a ram trace or via possibly eroded from an old cap, but I don't see anything physically wrong...

Anyway I'm just looking for insight more than anything else due to how the gameplay is affected by the severe graphical issues, I was leaning more toward RAM and I think I can just use the PC Engine schematics since they're roughly the same - but I don't want to waste all of that time if somebody more experienced would say it's the video chip, in which case I'd be able to use a donor from a PC Engine anyway, totally acceptable to me if that's the issue.

Anyway here's some images of what's being output onto the screen:






I actually intend to revert this back to stock since I found a spare screen once I fix this issue, just this really is easier for open air testing anyway, plug the sucker into my bench psu.
If it's actually the ram itself damaged I can check with some donor ram from a PC Engine before ordering replacements, again I just wanna save time by double checking what people may think the issue is more likely to be opposed to getting stuck in a rabbit hole of diagnosis

[Keith Courage]

Anything that looks like this I try ram first. If ram isn't the issue, then it's usually a faulty HU6270 but 95% of the time it's ram causing the problem.

[DrunkenMonk]

So interesting! I didn't even think of the HU6270, I did the ole close visual inspection of the chip and notice there's a whole leg just missing??. Low and behold I solder some kynar there and everythings looking absolutely perfect.

It was specifically leg 64, which is fairly close to cc502, which had leaked quite horrendously on this board, so I wonder if during using IPA + old toothbrush it was a little harsh and maybe I've brushed away a weakened leg? Going to be more mindful of that on future ones for sure...

But test was successful, time to undo the LCD mod and stock this puppy!




Thanks for the super helpful fast response, it made me really look closely to the board instead of giving it the know-it-all once over 

[Necromancer]

Congrats on fixing 'er!

[Keith Courage]

Glad it was an easy fix.