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Author Topic: Defender  (Read 2537 times)
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« on: November 20, 2005, 04:38:20 PM »

Game boots into rug pattern which repeats forever.

Pulled and tested all ROMs. The three old, gold-legged ROMs had broken legs. Replaced. No change.
Examination of CPU board shows signs of battery acid damage. Lots of green powder on and around
RAM sockets. Pulled all RAM and replaced with known working RAM. No change. Random probing of pins
of RAM chips with logic probe show lots of floating address/data pins. Replaced 12 of the 24 sockets.
Now all pins show nice pulsing and rug pattern looks better but it still never gets past it.
The pattern is not wiping across the screen normally.

Instead of scrolling smoothly from right to left like this:


It draws in two columns, like this:


I post these results on rgvac and am told by two people to check the 74153s. There are four of them.
Poking around with a probe, they all seem to be pulsing happily. One, however, has slightly different
sounds to the pulsing. There is a bit of corrosion on the pins. I pulled it and tested it in the
Allmax. No good.

I pull a 74153 from my bootleg Defense Command, pop it in and the game boots. Initial
tests indicate, unit ok.
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