Lunar Lander help

Anyone know what the Lunar Lander self test is supposed to do with respect
to a video display? My LL displays an image and plays in the normal game
mode, but doesn't display anything in the self test. Switches on the
control panel do activate sounds during self test though. I assumed that
the self test would behave similar to Asteroids so that I could see a cross
hatch style pattern on screen. Is LL self test supposed to be blind?

I wanted to see a cross hatch pattern so that I could more clearly identify
the problem I'm having with the video output. Basically, there's a vertical
column of video, about 2-3 inches wide that spans the entire height of the
display, starting at the left edge of the 4 digit score, fuel counters,
extending to the right. Video objects that are in this column get totally
distorted, almost as if stretched fully between the left and right edges.
Then, once the object passes out of this column, it regains its shape, and
looks normal again. The lunar terrain that occupies the space below turns
into a broken line that stretches from side to side. I'll have to take a
picture to give you a better description. It's really odd looking.

When I hook up a scope, the problem usually goes away! Hah. I finally
caught the problem on the scope, i.e. it's not a monitor defect. I've
noticed that the problem comes and goes, and has no relation to being first
powered on, or having the machine sit powered on for a while. The problem
essentially "drifts" in and out slowly. Given the drifting, it has a real
analog feel to it, like a bad cap somewhere, but I haven't gotten to the
point where I've located a candidate. I'm not convinced a cap could even do
this. I scoped the inputs to the DAC while having the problem, and the
inputs are all toggling. That in itself isn't a proof that the inbound
digital data is sane, but at least no inputs are stuck.

I'd certainly enjoy hearing any suggestions for what to look at. I'll try
to study the schematics some more, too. And if you think a picture might
help out or at least entertain you, I'll take one tomorrow and post it.

Regards,
Joel-

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Received on Thu Jun 19 20:26:32 2003