TECH: Defender Intermitent RAM Failure SOLVED!

[Rhett James Barnes]

I wanted to post the solution to my Defender "RAM Failure" in case it
might help anyone in the future. I would also like to thank everyone who
replied to the article and helped in person!!! Especially MacMan, who
offered the seeds to my finding the problem.

ABSTRACT:
Faulty 2532 ROM 3 on ROM board causes intermitent "RAM Failure" message
and video corruption that starts ~5 minutes after the game is turned on,
and stops about 20 minutes later, leaving the game funcitoning great the
rest of the day.

BACKGROUND:
Defender starts ok, runs for a few minutes. Then it starts to get a
couple of pixels of video corruption. Then it crashes, resets, and
returns with "Initial tests indicate RAM failure." The video corruption
gets worse, in jagged vertical lines, and becomes dynamic, with some pixes
flashing randomly. After about 20 minutes, the dynamic pixels stop. Then
the unit will reset, and run fine the rest of the day.

SOLUTION:
Electronics is not my trade, so the search was doomed from the beginning.
I had checked easy stuff like interconnects, the power was getting cleanly
to the RAMs, and I had swapped out all the RAMs. It was hard to trouble
shoot with heat/cold, because the game seemed to work fine cold and warm,
just not luke-warm. I did waste a lot of freon on the thing. I also
checked that the RAMs were getting refresh.

I tried swapping a couple chips on the CPU. I had heard that the PIA on
the ROM board could cause similar problems so I looked here. That didn't
fix it, but I did notice that cutting the connection between the CPU and
ROM board stopped the dynamic garbage. I didn't know whether this was
just because the machine had crashed, or whether there really was garbage
coming off the ROM board.

Well, make a long story short, pulling ROM 3 (hey, I'll mess with the
socketted stuff first!) stopped the corruption. Replacing it left me with
a working game!!!

Thanks again to everyone offering help!

FOLLOW-UP:
Am I the only one out there who wastes time "fixing" these thing, instead
of just swapping boards out? I've so far had to revive the Interface,
Sound, and ROM (three times) boards from the dead. This means I would
have been left with only one original board in my game had I just given up
and replaced them! I guess it would have saved a lot of time. But I'm
not a "collector" by the definition of the group, meaning I'm not a
trader. I want to keep the games I have, and it just feels good to make
them work. I'm willing to waste time on them, because I don't have a high
volume through-put here. Besides, I don't just have boards lying around
like everyone else!

But I feel like a real loser when I tell someone how I fixed this or that,
because they'll just ask me why I didn't just swap it out. Maybe it's
just me. But it did come in handy reviving my Space Firebird, for which
no one would offer me the board I needed!!!

[Commander Dave]

Actually, I have started trying to fix boards and monitors. But I do
admit at this point that I usually have to have another working
boardset side by side (I'm just learning).

I have had mixed success with the monitor repair. Some good, some bad,
but it is fun and it gives me satisfaction when I get something fixed
like that and also that I saved a game board from the junkpile.

More random thoughts,
-Commander Dave

On Wed, 08 Sep 1999 21:04:32 -0700, cryor...@aol.com (Rhett James
Barnes) wrote:

<<snip>>