re:Star Wars Repair Story (long)

In message "Star Wars Repair Story (long)", you write:
>The Star Wars game I had would have no stars and the Tie fighters would never
>come out. After a while, the graphics would become more and more
>screwed up.
>The self test indicated "Matrix errors". And dumped out a bunch of hex.
>
>I figured out one of the Mathbox ROMS was bad (#113), by comparing them to
>the images on tant.com. I got the correct image and programmed a battery-backed
>8kx8 SRAM with the data. Then I rigged a temporary board which mapped the
>bottom 4 bits of the first 1K of memory into the socket on the main board and voila
>- It's all better now!

Believe it or not this is VERY VERY old news. These PROMs have been failing
for YEARS. I personally have fixed dozens of them and have posted this
solution to the net many times.

>(BTW, I struggled for a few days until I realized my bench was wired up with
>wire that was too skinny! So, I built a nice thick wire harness for +12 and +5)

DOH!

>Now I simply need a more permanent solution, as they don't make those
>signetics PROMS anymore. Maybe this is a common need?

Actually, they are not at all hard to find and, I recently discovered and
posted to the newsgroup that around half of these PROM failures are merely
1->0 bit rot and they can be reprogrammed for a nother decade or so of use.

>I have seen three boards with this failure. Would a small board which plugs into the
>mathbox ROM sockets and replaces them with 2764's be useful to anyone else?
>It seems like this could extend the life of these boards considerably, because the
>Signetics 82S137's run mighty hot and seem to die young, and you can't get them
>anymore.

WOuld be nice but I don't think it is worth it.

--
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