TECH: Pac-Man displays all zeros

Archived from groups: rec.games.video.arcade.collecting (More info?)

Hello all,
Usually I can figure these Pac-Man pcb's out, but this one has me stuck.
When powered up, it displays a screen full of zeros....there is a bit of
flickering sprites in the right hand corner, kinda behind the zeros. Here's
what I know...All ROM's are good, all 2114's are good, both satellite boards
are good. All sockets were replaced....problem remained. Pin thirteen of the
2114's at 4N/4P/4R is stuck low. All the other lines seem alright. The
74LS245 that this line runs to is good. the line is stuck low on both sides
of the 245. The only other abnormality that I can find is the IRQ ON line is
pulsing wildly. I traced this signal back to the 259 at 8K where it's still
pulsing wildly....all inputs to 8K look normal. Replaced 8K...problem
remained...That's where I'm at so far. Any suggestions are greatly
appreciated.

Thanks!
Edward
groundz@prodigy.net
6 answers Last reply
More about tech displays zeros
  1. Archived from groups: rec.games.video.arcade.collecting (More info?)

    ed,

    When I have sprites in the lower right hand corner, I start looking at
    7L and the logic in the vicinity. This is of course ASSUMING you have
    done the basic troubleshooting in the processor and clock circuits and
    checked the watchdog system. Good luck.

    - Matt
  2. Archived from groups: rec.games.video.arcade.collecting (More info?)

    I had this recently as well. It was solved by reseating the sync-buss
    card. I know you said you tried that but there might be something
    wrong with that board as well. If you go to
    http://users.erols.com/mowerman/pacfile.htm, about a quarter of the way
    down you'll read:

    "U0 74LS139 if this fails the symptom will be the static garbage on
    screen. You can quickly diagnose this failure with a logic probe. Be
    sure that you have pulsing activity (full range high to low) on the
    input pins 3, 16 & 27 of the Z80 SBC (the 28 pins that connect the SBC
    to the main circuit board). Next check for ouput at pin 17. (You may
    want to look for pulsing at pins 10 & 12 of the 74LS139 also)."

    I'm not an expert but I'll throw that idea out. Good luck!

    --jake
  3. Archived from groups: rec.games.video.arcade.collecting (More info?)

    Thanks Matt!

    Processor is fine....clock looks good....oops...and make that--sprites are
    in the lower left hand area.

    Edward
    "Matty-t" <matthews@audio-doctors.com> wrote in message
    news:1114463219.172505.145640@f14g2000cwb.googlegroups.com...
    > ed,
    >
    > When I have sprites in the lower right hand corner, I start looking at
    > 7L and the logic in the vicinity. This is of course ASSUMING you have
    > done the basic troubleshooting in the processor and clock circuits and
    > checked the watchdog system. Good luck.
    >
    > - Matt
    >
  4. Archived from groups: rec.games.video.arcade.collecting (More info?)

    The trouble shooting manual says all zero's is the 2114's at position 4K and
    4N
    11 rows of zero's is the 74LS08 at 7H


    "Edward Lutz" <groundz@prodigy.net> wrote in message
    news:Gv6be.507$6z3.354@newssvr33.news.prodigy.com...
    > Hello all,
    > Usually I can figure these Pac-Man pcb's out, but this one has me stuck.
    > When powered up, it displays a screen full of zeros....there is a bit of
    > flickering sprites in the right hand corner, kinda behind the zeros.
    > Here's what I know...All ROM's are good, all 2114's are good, both
    > satellite boards are good. All sockets were replaced....problem remained.
    > Pin thirteen of the 2114's at 4N/4P/4R is stuck low. All the other lines
    > seem alright. The 74LS245 that this line runs to is good. the line is
    > stuck low on both sides of the 245. The only other abnormality that I can
    > find is the IRQ ON line is pulsing wildly. I traced this signal back to
    > the 259 at 8K where it's still pulsing wildly....all inputs to 8K look
    > normal. Replaced 8K...problem remained...That's where I'm at so far. Any
    > suggestions are greatly appreciated.
    >
    > Thanks!
    > Edward
    > groundz@prodigy.net
    >
  5. Archived from groups: rec.games.video.arcade.collecting (More info?)

    Thanks. Sync-buss card is good. I tested it on a known working board. Just
    to be sure...I also put a new socket under it.

    Edward
    <jake.vanorder@gmail.com> wrote in message
    news:1114478658.246473.108620@o13g2000cwo.googlegroups.com...
    >I had this recently as well. It was solved by reseating the sync-buss
    > card. I know you said you tried that but there might be something
    > wrong with that board as well. If you go to
    > http://users.erols.com/mowerman/pacfile.htm, about a quarter of the way
    > down you'll read:
    >
    > "U0 74LS139 if this fails the symptom will be the static garbage on
    > screen. You can quickly diagnose this failure with a logic probe. Be
    > sure that you have pulsing activity (full range high to low) on the
    > input pins 3, 16 & 27 of the Z80 SBC (the 28 pins that connect the SBC
    > to the main circuit board). Next check for ouput at pin 17. (You may
    > want to look for pulsing at pins 10 & 12 of the 74LS139 also)."
    >
    > I'm not an expert but I'll throw that idea out. Good luck!
    >
    > --jake
    >
  6. Archived from groups: rec.games.video.arcade.collecting (More info?)

    All 2114's are good. I tested them on a known working board. All their
    sockets were also replaced.
    "Terry" <congdar@hotmail.com> wrote in message
    news:cOhbe.4731$yc.86@trnddc07...
    > The trouble shooting manual says all zero's is the 2114's at position 4K
    > and 4N
    > 11 rows of zero's is the 74LS08 at 7H
    >
    >
    >
    > "Edward Lutz" <groundz@prodigy.net> wrote in message
    > news:Gv6be.507$6z3.354@newssvr33.news.prodigy.com...
    >> Hello all,
    >> Usually I can figure these Pac-Man pcb's out, but this one has me stuck.
    >> When powered up, it displays a screen full of zeros....there is a bit of
    >> flickering sprites in the right hand corner, kinda behind the zeros.
    >> Here's what I know...All ROM's are good, all 2114's are good, both
    >> satellite boards are good. All sockets were replaced....problem remained.
    >> Pin thirteen of the 2114's at 4N/4P/4R is stuck low. All the other lines
    >> seem alright. The 74LS245 that this line runs to is good. the line is
    >> stuck low on both sides of the 245. The only other abnormality that I can
    >> find is the IRQ ON line is pulsing wildly. I traced this signal back to
    >> the 259 at 8K where it's still pulsing wildly....all inputs to 8K look
    >> normal. Replaced 8K...problem remained...That's where I'm at so far. Any
    >> suggestions are greatly appreciated.
    >>
    >> Thanks!
    >> Edward
    >> groundz@prodigy.net
    >>
    >
    >
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