Tempest AVG board problem

Hi guys,
Got a Tempest board problem I've been struggling with. Took me a while to get
the 6100 rebuilt, only to find out I've got a board problem. Here's a video of
the problem I was originally having.

http://www.youtube.com/watch?v=Bt4Hj9NEdRM

Problem 1:
I've tested the board in a working Tempest, and determined the Vector Generator
board contains the fault. Aux board and board connector cable were both
verified good.

In the machine I tested in, my board showed horizontal collapse, as opposed to
what you see in the video.

Problem 2:
Since bringing it back home, I cleaned and reseated 5 RAMs that were socketed.
Now, I have no X/Y output voltage at all (I had scrolling voltages before).
Game still plays blind. I simply lost my XY output voltages.

I've been having another local friend/collector help me with this, and here's
what we've done so far... Tested a bunch of chips in the Vector Generator
Address Selector, Data Shifter, and Vector Timer sections of the board using a
logic comparator, which all tested good. I don't have every 74LS chip that is
used on the board so I can't test all sections, but I feel like some main
problem areas are eliminated.

Logic probe confirms data is flowing in the RAMs and the vector generator
sections.

I have had it in test mode with no difference. Here are some tests I ran
yesterday (you'll notice I now have voltages as of yesterday, but they are not
scrolling):

X Out > +2.765 steady. Can make it go up or down by adjusting size pots.
Y Out > +2.622 steady. Can make it go up or down by adjusting size pots.
Test lug @C88 > -15.18
Test lug @C61 > +15.26
C60 > -15.19
C62 > +15.25
D/E12 pin 4 > -15.19
D/E13 pin 4 > -15.19
A/B12 pin 2 > +15.25
A/B13 pin 2 > +15.25
D10 pin 3 > -15.19
D10 pin 13 > +5.10
D10 pin 14 > 0 (reads +15.25 at R108)
D10 pin 16 > -8.18 <-- ?????

Edge connector
W > -24.18
X > +23.89
readings the same at other +-22v pins

Spot killer's on as there are no scrolling voltages going up to the monitor.

I'm going to test voltage and logic probe some chips (E6/F6) that supply the
LS194 chips in the vector generator data shifter section and see what I get. I
believe all the output pins of those 194s are stuck low.

Am I warm? Is there anything else I should be checking? Not exactly sure what
I'm missing, but my money is on a bad DAC312 somewhere...

Thanks,
Scott

      
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Received on Tue Aug 24 23:38:31 2010