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External
Since: Mar 06, 2005
Posts: 130
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(Msg. 1) Posted: Mon Feb 27, 2006 9:55 pm
Post subject: TECH: _Pac Man_ board resetting
Archived from groups: rec>games>video>arcade>collecting (more info?)
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I've got a _Pac Man_ board (a Midway original) that's really making me
scratch my head. It consistently resets at the same point in the program.
Upon boot-up, it goes through the cycles of garbage, and when it's trying to
post the grid screen, you see it for just an instant -- and then the board
resets. This cycle continues indefinitely.
What's strange is, if you put the board into self-test, it passes! No
problem at all. "MEMORY OK," it displays the DIP switch options, and it
responds to inputs and plays sounds.
I can tell you what is definitely NOT the cause (please read carefully!):
* NOT the Z-80.
* NOT the four ROMs for the program.
* NOT the 2114 RAM chips.
* NOT the plug-in daughtercards.
All of these have been swapped out with known-good replacements. No change.
I'd appreciate any help on this. Thanks!!!!
Matt J. McCullar |
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External
Since: Nov 24, 2005
Posts: 54
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(Msg. 2) Posted: Mon Feb 27, 2006 9:55 pm
Post subject: Re: TECH: _Pac Man_ board resetting [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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External
Since: Aug 21, 2005
Posts: 322
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(Msg. 3) Posted: Mon Feb 27, 2006 9:55 pm
Post subject: Re: TECH: _Pac Man_ board resetting [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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External
Since: Apr 03, 2005
Posts: 370
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(Msg. 4) Posted: Mon Feb 27, 2006 10:55 pm
Post subject: Re: TECH: _Pac Man_ board resetting [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Have you replaced any of the sockets (Z80, 284, 285, etc)?
I've seen all three of these cause this type of problem,
but your mileage may vary.
Also, have you tried any diagnostic ROMs or boards on it
(ABC kit), etc.? Had a board that kept rebooting and it
turned out the watchdog was bad, but the ABC kit will
still boot w/a bad watchdog and tell you it's bad.
Scott C.
Matt J. McCullar wrote:
> I've got a _Pac Man_ board (a Midway original) that's really making me
> scratch my head. It consistently resets at the same point in the program.
> Upon boot-up, it goes through the cycles of garbage, and when it's trying to
> post the grid screen, you see it for just an instant -- and then the board
> resets. This cycle continues indefinitely.
>
> What's strange is, if you put the board into self-test, it passes! No
> problem at all. "MEMORY OK," it displays the DIP switch options, and it
> responds to inputs and plays sounds.
>
> I can tell you what is definitely NOT the cause (please read carefully!):
>
> * NOT the Z-80.
> * NOT the four ROMs for the program.
> * NOT the 2114 RAM chips.
> * NOT the plug-in daughtercards.
>
> All of these have been swapped out with known-good replacements. No change.
>
> I'd appreciate any help on this. Thanks!!!!
>
> Matt J. McCullar
>
>
> >> Stay informed about: TECH: _Pac Man_ board resetting |
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External
Since: Aug 21, 2005
Posts: 322
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(Msg. 5) Posted: Tue Feb 28, 2006 9:33 pm
Post subject: Re: FIXED!!!!! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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External
Since: Mar 06, 2005
Posts: 130
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(Msg. 6) Posted: Tue Feb 28, 2006 9:55 pm
Post subject: FIXED!!!!! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Whew! I _finally_ found it today!!!! The problem turned out to be -- get
this -- a bad 74LS161 at location 9C. This is indeed part of the watchdog
circuit. Problem was, it's a four-bit counter, but only two of the bits
were counting properly!!!! That means it was sending a reset pulse to the
Z-80 instead of being cleared like it's supposed to be. Replacing that chip
cured it.
An X-Y test revealed nothing wrong with this chip; I found it by desoldering
it and testing it in several pieces of test gear. It failed on all of them.
I'd love to show everybody a picture of it, but it didn't survive the
beating I gave it with a sledgehammer. >> Stay informed about: TECH: _Pac Man_ board resetting |
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External
Since: Apr 03, 2005
Posts: 370
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(Msg. 7) Posted: Tue Feb 28, 2006 9:55 pm
Post subject: Re: FIXED!!!!! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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External
Since: Mar 06, 2005
Posts: 130
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(Msg. 8) Posted: Wed Mar 01, 2006 8:55 pm
Post subject: Re: FIXED!!!!! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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"Matty-t" <matthews.TakeThisOut@audio-doctors.com> wrote in message
news:1141191205.415633.114190@e56g2000cwe.googlegroups.com...
> Three paragraphs and I don't see a thank you anywhere =\
>
> Your welcome!!
>
> - Matt
You're right, of course. I apologize. That occurred to me earlier today.
THANK YOU, everyone! Hope you don't get a head-scratcher problem like this
one!!!
Matt J. McCullar
The Grateful >> Stay informed about: TECH: _Pac Man_ board resetting |
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External
Since: Feb 15, 2006
Posts: 97
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(Msg. 9) Posted: Thu Mar 02, 2006 6:55 am
Post subject: Re: FIXED!!!!! [Login to view extended thread Info.]
Archived from groups: per prev. post (more info?)
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Matt J. McCullar wrote:
>
> "Matty-t" <matthews.DeleteThis@audio-doctors.com> wrote in message
> news:1141191205.415633.114190@e56g2000cwe.googlegroups.com...
>> Three paragraphs and I don't see a thank you anywhere =\
>>
>> Your welcome!!
>>
>> - Matt
>
> You're right, of course. I apologize. That occurred to me earlier today.
> THANK YOU, everyone! Hope you don't get a head-scratcher problem like
> this one!!!
Constant resetting caused by a bad watchdog is hardly a headscratcher  >> Stay informed about: TECH: _Pac Man_ board resetting |
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