Defender Rom Board Layout

by Bob Roberts

The Williams rom boards seem to pose a problem for everyone, in some manner or another, so I thought I would put this pic up here to hopefully answer a lot of repeat questions.

I guess it is no wonder that it is a stumbling block for some, since the labels are often times upside down or worse, intermixed from previous repairs with eproms from other games with the labels in the opposite direction, and from new eproms with their different looking labels, regardless of direction. Then there is the row deviation placing 10/11/12 in the center, and I don't know how many times I got games in with the roms simply out of position....sometimes with the whole field inverted, I guess due to installing the roms without realizing which way was up.

Which way is up? That's another question still asked frequently, tied into.. I want to know which way to read the four LEDs to locate my problem or simply which LED is number one. The picture below should answer all questions regarding layout. All pin 1 positions are marked with a red dot, and the top line on each rom is it's position, the center line is the type of eprom used, and the bottom line is the checksum for that rom.

I get asked about the difference between the red label & the white label with the red stripe quite often. It is my opinion that there is no difference. The checksums are the same and the white & red stripe labels on various boards, show no particular pattern of striping from one chip to next, let alone from rom board to rom board. On that basis, I drew the conclusion that they simply didn't have the red labels available at the time of release in 1980 and striped them with a red marker of some sort. When the 1981 red labels turned up on the scene, I read them into my programmer & ran the comparison test on them, only to find no differences.

Happy Gaming...........

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