I once had an issue where x was only deflecting positive, hence could be
interpreted as a small swing. turns out the most significant bit going
into the dac, is ths sign bit, and it was borked.
here is an exerpt from my post
" However, hooking up my scope to the xy outputs, show a nasty screen.
Looks like X is only positive, and Y was noisy. The nois apperaed to be
eminating from the op amp tl082 at bc8, so I pulled and swapped it. Y
now looks good.
Not really understanding much about these vector generators, I decided
to socket the rest of the op amps and swapped them from x to Y. The
problem with X only being positive stayed with X. I then socketed and
swapped the A to D converters and again the problem stayed with X.
Looking at the vector List archives, I found a post from a few years ago
that indicated the MSB going into the DAC could be at fault.
Furthermore, I found a link to a website "the secret life of a vector
generator" which enlightened me on the operation of the circuit, and
indeed, the MSB going into the DAC was likely to blame. I swapped the
74174 at D6 after my logic comparitor hinted that was a problem with pin
7. All was good! "
Mike
________________________________
From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Kevin Moore
Sent: Tuesday, April 13, 2010 9:41 AM
To: vectorlist@vectorlist.org
Subject: Re: VECTOR: Omega Race
Ok the reset seemed to be a combo of a slightly flaky CPU. It tests
good, and works in my other games, but this one doesn't seem to like it.
So I swapped the CPU, and adjusted the +5 to 5.10 No more watchdog.
Had a bad tl082 in Y. Replaced and now I'm seeing something in both x
and y on the scope, but when I put it in xy mode it seems a blurry, you
can't really make out anything you can see objects moving, but can't
tell what they are. :(
The ac voltages on the x output is around 2 - 2.5 volts, but the y is
still less than 1vac. I'm used to dealing with Atari so the y seems like
it might be low.
Anyone know what the voltages should swing around?
Kevin
On Mon, Apr 12, 2010 at 3:31 PM, <mike.ranger@arcelormittal.com> wrote:
I *think* that the 6 second thing may be due to the vector
generator getting screwed up. I have aboard doing the same thing, last
I looked at it. I never did track it down.
________________________________
From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Kevin Moore
Sent: Monday, April 12, 2010 4:29 PM
To: vectorlist@vectorlist.org
Subject: Re: VECTOR: Omega Race
Well Long test turned up nothing.
However. PB Junkie might be correct. I pulled the 5101 and It's
no longer in a constant state of reset. Now it will reset every 6
seconds or so. But I'm seeing some output on my O-scope now!! WOOT.
Making some headway.
Thanks Mike..
I'll keep digging and see what else I can find.
On Mon, Apr 12, 2010 at 3:14 PM, <mike.ranger@arcelormittal.com>
wrote:
Yup. I would also pull the settings ram (5101 at S4)
just in case. I seem to recall some peanut-brittle junkie out there
claiming the a bad 5101 was causing some havoc, and it is harder to test
on the fluke.
Once everything passes Fluke tests, and it still dogs,
you have to dig into the cpu signals and power conditioning, me thinks.
Mike
________________________________
From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Kevin Moore
Sent: Monday, April 12, 2010 4:08 PM
To: vectorlist@vectorlist.org
Subject: Re: VECTOR: Omega Race
Good point on the long test.
The areas I'm testing are
4000-4bff
and
8000-8fff
Those the two you talking about?
They are all socketed so I pulled and checked them with
my BK 575 first. That's when I found the open traces eaten by battery
acid. :( Replaced sockets, and re-bridged bad traces. There were only a
couple of bad spots.
On Mon, Apr 12, 2010 at 3:00 PM,
<mike.ranger@arcelormittal.com> wrote:
Make sure you do the ram tests on both banks,
and do the long test! I had one pass the short test on the vector ram,
but failed the long test!
Mike
________________________________
From: owner-vectorlist@vectorlist.org
[mailto:owner-vectorlist@vectorlist.org] On Behalf Of Kevin Moore
Sent: Monday, April 12, 2010 3:56 PM
To: vectorlist@vectorlist.org
Subject: VECTOR: Omega Race
Ok so I'm working on an Omega Race. My first
one..
Cleaned up the Acid damage, and my fluke now
reports nothing but good things for the Ram/Rom/and Bus check..
However my CPU is still watch dogging. Is there
any repair info out there, or where should I go from here?
BTW I hate Midway Schematics..
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Received on Tue Apr 13 10:08:35 2010
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