MAMEWorld Forums - The Loony Bin

> The suspect chips share a common output enable signal (/TROE.C1X). I'd check that out
> first: it originates at pin 17 of the 74ALS541 @ U43, which has a 100 ohm resistor on
> its output.
>
> Otherwise, here's a source of VRAM chips if you need them:
>
> http://cgi.ebay.com/?viewitem&item=390601177814

OK, here's a weird thing. When I first power the board up, the video appears mostly blue-green. But when I touch U5-pin27 to ground just for a second, the screen blinks and snaps into more of a full-color mode still fuzzy with lines only the background appears black and the lines are white. It stays like this until I power down.

When I touch and hold U43-pin17 to ground, the screen goes almost completely white for a second or two until the graphics refresh and the white lines seem to lighten up but the screen still looks very static-y. When I run the CPU test while grounding U43-pin17 it still fails but this time it shows some of the ROMs to be bad and stops, leaving the RAM untested. Without grounding anything it tested the RAM and then stopped. The original results remain the same when not grounding anything.

That VRAM source is a good price and he combines shipping! But the speed on the original RAM chips was -10 and the ones on eBay are -15 (slower). Would that make a difference?

Overall, I am putting it on the back burner for now. I told the guy who bought it he has 3 choices if he doesn't want me to try and fix it: contact the seller and complain, try to sell for himself as partially working or hang on the wall as art. I'm sure the seller will say he isn't responsible for a 20+ year old board and that it was working when he had it.