[Russ]

I have about four Neo Geo six slot arcade game boards with Video RAM
errors. It is not the actual video RAM, that much I have determined.
If your not familiar with this board it has a lot of large surface
mount chips with upwards over over a hundred pins each. It uses a
Motorola 68000 chip. Can someone give me some clues on how to track
this problem down? With this kind of error am I going to find an
address or data line that is stuck high or low? Or could it be another
pin. Nothing on the M68000 seems wrong, The chip checks out fine on a
tester. I have replaced the video RAMS and this M68000 so it must be
in another chip or in a trace. If I probe each and every pin of all of
the components would I for sure find the error or can this type of
error not show up as a hardware difference? Can this be a software
error? Lets say I find the pin that is not working, What would that
pin look like on a scope? Just a high 5 volt or low ground, or could
it be at a logic high or low, that it is just not transitioning from
one state to the next as it supposed to? Could it be more then one
pin? There is no documentation for this board at all. I am not sure
where to began and what to do next.
Thanks very much
Russ

[Franc Zabkar]

On Sat, 28 Feb 2009 15:27:04 -0800 (PST), Russ
put finger to keyboard and composed:

I have about four Neo Geo six slot arcade game boards with Video RAM
errors. It is not the actual video RAM, that much I have determined.
If your not familiar with this board it has a lot of large surface
mount chips with upwards over over a hundred pins each. It uses a
Motorola 68000 chip. Can someone give me some clues on how to track
this problem down? With this kind of error am I going to find an
address or data line that is stuck high or low? Or could it be another
pin. Nothing on the M68000 seems wrong, The chip checks out fine on a
tester. I have replaced the video RAMS and this M68000 so it must be
in another chip or in a trace. If I probe each and every pin of all of
the components would I for sure find the error or can this type of
error not show up as a hardware difference? Can this be a software
error? Lets say I find the pin that is not working, What would that
pin look like on a scope? Just a high 5 volt or low ground, or could
it be at a logic high or low, that it is just not transitioning from
one state to the next as it supposed to? Could it be more then one
pin? There is no documentation for this board at all. I am not sure
where to began and what to do next.
Thanks very much
Russ

I don't know anything about your console, but here are some Wikipedia
links:
http://en.wikipedia.org/wiki/Neo_Geo_(console)
http://en.wikipedia.org/wiki/File:Neomb.jpg

The video RAM looks like it may consist of three parts:

=================================
Main Video memory : 74 KB

Video Memory: 64 KB
Palette Memory : 8 KB
Fast Video RAM : 2 KB
=================================

Do you have a photo of your boards, and can you identify the RAM ICs?

I think it's unlikely that all of your boards have trace problems, so
I'd be looking for faulty chips. It would be helpful if the error
report (?) displayed the good and bad data so that a particular bit
could be identified. I doubt that you have a stuck address line or
data line, as the same bus would probably be shared by the EPROM/PROM
and main memory. OTOH, if either bus is buffered, then the buffer may
be suspect. Does the screen display anything at all? Is the output
garbled? Are there vertical lines of stuck bits? Were your replacement
RAMs correctly rated for speed? Are they DRAMs or SRAMs?

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

[Michael Kennedy[_3_]]

"Russ" wrote in message
...

I have about four Neo Geo six slot arcade game boards with Video RAM
errors. It is not the actual video RAM, that much I have determined.
If your not familiar with this board it has a lot of large surface
mount chips with upwards over over a hundred pins each. It uses a
Motorola 68000 chip. Can someone give me some clues on how to track
this problem down? With this kind of error am I going to find an
address or data line that is stuck high or low? Or could it be another
pin. Nothing on the M68000 seems wrong, The chip checks out fine on a
tester. I have replaced the video RAMS and this M68000 so it must be
in another chip or in a trace. If I probe each and every pin of all of
the components would I for sure find the error or can this type of
error not show up as a hardware difference? Can this be a software
error? Lets say I find the pin that is not working, What would that
pin look like on a scope? Just a high 5 volt or low ground, or could
it be at a logic high or low, that it is just not transitioning from
one state to the next as it supposed to? Could it be more then one
pin? There is no documentation for this board at all. I am not sure
where to began and what to do next.
Thanks very much
Russ

Maybe someone here can give you a hand.