SNK Neo Geo Pocket Color Screen Problem

[GadgetUK]

I've recently purchased a Neo Geo Pocket Color which had bad corrosion from acid. I've cleaned it all up and neutralized it etc and the system has been working fine but it seems that it only displays at the right colors / contrast for a short period of time. After a minute or two the contrast or color doesn't look quite right, almost like a capacitor problem or something.

Has anyone seen that behaviour before? Looking for some pointers - schematics would be nice but I guess they were never released?

EDIT: The corrosion was only located around the power input prongs, with a little corrosion on the same area on the opposite side of the board - ie. just around the common ground on the outer bottom edge of both sides of the board.

Could it be related to the trim pot? - that was heavily corroded and wont move.

 

[GadgetUK]

I've worked out that the problem starts after 5 mins or so and ends up with striations on screen - a bit like when an LCD starts to fail. If I move my finger over a couple of components near battery connections the picture instantly goes perfect. I think I've got a missing ground connection there somewhere. Damn near impossible to work out without schematics or one to compare to...

 

[GadgetUK]

Well it looks like I've resolved this... It was a real pain in the *** to work out but I eventually relocated another resistor that was barely connecting to the pads - the other 10K resistor related to the contrast pot. I also reflowed more components on there with loads of flux and did the same flux and solder treatment to several vias. It has been running for 2 or 3 hours without issue now. Previously it would start to loose contrast or something after maybe 5 minutes to the point it was hard to see. The other problem was that after that 5 or 10 minutes you would see striations down the screen (like when an LCD starts to fail), but after reflowing the vias that problem stopped also.

 

[xsq]

yay! A NGPC brought back to life.