Re: Tempest AVG board problem

What do you have on pins 1 and 11 of the ls194's ? Probe those with the
logic probe. You may have a bad 12Mhz clock, or a bad latch.

On Tue, Aug 24, 2010 at 10:38 PM, Scott Zeiser <scott@zeiser.org> wrote:

> 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 23:55:00 2010