Tempest/LV2000 Questions -- Update

Hello, I've gotten a few responses, and I'm still working on the problem.
But I've made some progress...

After learning that the monitor is made up of relatively independents
circuit components, I started testing each of them to isolate where the
problem began to surface:

1) Nothing plugged in but the power transistors, both diodes are lit
brightly.
2) Power transistors + deflector circuits, the (+) diode fades.
3) Everything minus the deflector, both diodes are lit brightly.

So this seems to be something w/ the two X/Y deflector circuits. I wanted
to see if I could isolate either the X or the Y, so I tried the experiment
of hooking only one direction up. Of course the spot-killer kicks in, so I
disconnected the blue/white wire for these two tests.

With the monitor laying horizontal on my table:
The X shows a horizontal line, but only on the left side. Reaching the far
left, but not reaching the middle.
The Y shows a vertical line, but only on the bottom side. Reaching the far
bottom, but not reaching the middle.

I didn't succeed in isolating one over the other, but I did notice each axis
was able to stretch farther (from edge to middle) when alone than they were
when both were connected. Another observation was the X-axis caused
noticeably more dimming to the diode than did the Y-axis (both caused
dimming). Particularly a point in the game about 7-10 seconds into startup
that really seems to do something heavy on the screen.

I then decided to check the voltages from the power transistors:
1) Just the power transistors, output is around +/-25V.
2) Deflectors plugged in, the positive voltage reads between 0V and down to
-1.5V. (Not +25V)

Ok, sounds like a short? By why do I get any deflection at all then?

So... Can anyone offer suggestion of where to go from here? Anyone know of
some reference that explains how the image is translated (mathematically)
from input to screen?

And two other questions I'm hoping someone could answer, if only to explain
why it happens:

--From: http://www.bithose.com/serfaq/REPAIR/F_VAtari7.html#VATARI_010
"Distorted image which exists ONLY in the lower right quadrant of the
display. ...the problem has always been a bad ZD101..." Can someone explain
why a failur in the LV section would cause the symptom? The LV2000 removes
the ZD, but maybe knowing why it causes the symptom can help me track down
where mine is at fault.

--While I was testing just the power transistors plugged in, I forgot to
remove the plug to the HV. Turned it on, and after 14 seconds, the + diode
on the LV2000 went off (and so did the spot killer). It didn't fade, it
just turned off. Tried it again, same results. Just wondering if someone
could explain what takes 14 seconds to kick in?

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Received on Mon May 21 12:50:41 2001