Space Invaders video invert problem

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

First things first - this is a Nichibutsu Moon Base 3-layer boardset.
The problem *definitely* lies with the ROM board. a Taito ROM board
works fine if swapped out with this dodgy Moon Base ROM board.

Problem as follows - in cocktail mode for player one the the
grraphics, letters and numbers are flipped vertically so appear upside
down. When switching to player 2 the screen flips correctly and text,
graphics and numbers are the correct way around.

I have spent hours searching through the relevant parts of the video
invert circuitry on the ROM board - checked out all relevant signals
(even compared against a working Taito ROM board and cannot see any
obvious differences on the 'scope). Replaced the LS83's at locations
3D and 3E( locations 26 and 27 on a Taito S.I. ROM board) and the LS86
responsible for the video inversion. Have checked for shorts on both
inputs and outputs, broken tracks, weak signals - tried pulling up
certain signals, etc, etc, etc but all to no avail.

I'm hopelessly stumped.

Can anyone give me any ideas please on anything else that I might try?


Thanks
10 answers Last reply
More about space invaders video invert problem
  1. Archived from groups: rec.games.video.arcade.collecting (More info?)

    try http://www.elektronforge.com

    He repairs boards. Very reasonably.

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

    On 21 Jul 2005 15:19:45 -0700, "RJ" <northrnrjf@aol.com> wrote:

    >try http://www.elektronforge.com
    >
    >He repairs boards. Very reasonably.

    Thanks. At this stage though I'm just hoping for a tech tip or two
    that will point me in the right direction. :-)
  3. Archived from groups: rec.games.video.arcade.collecting (More info?)

    On Thu, 21 Jul 2005 21:49:27 GMT, max-man@hotmail.com (max-man) wrote:


    >Problem as follows - in cocktail mode for player one the the
    >grraphics, letters and numbers are flipped vertically so appear upside
    >down. When switching to player 2 the screen flips correctly and text,
    >graphics and numbers are the correct way around.

    I should clarify that a bit more - everything is *in the right place*
    for the player one display, ie the display is the right way up with
    laser base to the bottom, etc it's just that the characters and
    graphics haven't been flipped.

    IYSWIM. :)

    So for player one you would normally see:


    ZZZZZZZZZZZ


    AAAAAAAAAAA


    where the A's represent characters and graphics at the bottom and Z's
    are characters and graphics at the top. The A's on this board are
    still at the bottom and Z's at the top, it's just that they're in
    their correct places but upside down. Same apllies to anything in the
    middle as well of course.

    When the display flips for player two then all looks fine, ie A's are
    then at the top (looking at it from player one's position) and Z's at
    the bottom as they should be, but they are the correct way around for
    player two.
  4. Archived from groups: rec.games.video.arcade.collecting (More info?)

    Do the Roms check good? can you run the Taito rom set in the other board or
    is one 2716 and the other 2708?


    "max-man" <max-man@hotmail.com> wrote in message
    news:42e027fc.66281468@news.freeserve.net...
    > On Thu, 21 Jul 2005 21:49:27 GMT, max-man@hotmail.com (max-man) wrote:
    >
    >
    >>Problem as follows - in cocktail mode for player one the the
    >>grraphics, letters and numbers are flipped vertically so appear upside
    >>down. When switching to player 2 the screen flips correctly and text,
    >>graphics and numbers are the correct way around.
    >
    > I should clarify that a bit more - everything is *in the right place*
    > for the player one display, ie the display is the right way up with
    > laser base to the bottom, etc it's just that the characters and
    > graphics haven't been flipped.
    >
    > IYSWIM. :)
    >
    > So for player one you would normally see:
    >
    >
    > ZZZZZZZZZZZ
    >
    >
    >
    > AAAAAAAAAAA
    >
    >
    > where the A's represent characters and graphics at the bottom and Z's
    > are characters and graphics at the top. The A's on this board are
    > still at the bottom and Z's at the top, it's just that they're in
    > their correct places but upside down. Same apllies to anything in the
    > middle as well of course.
    >
    > When the display flips for player two then all looks fine, ie A's are
    > then at the top (looking at it from player one's position) and Z's at
    > the bottom as they should be, but they are the correct way around for
    > player two.
    >
    >
  5. Archived from groups: rec.games.video.arcade.collecting (More info?)

    On Fri, 22 Jul 2005 08:38:54 +0100, "simon hanlon"
    <simonjhanlon@btopenworld.com> wrote:

    >Do the Roms check good? can you run the Taito rom set in the other board or
    >is one 2716 and the other 2708?

    The original Moon Base ROMs were fine but I've now carried out the
    single chip mod so it uses a single 27128 instead.
  6. Archived from groups: rec.games.video.arcade.collecting (More info?)

    I have seen this problem before, but i don't seem to have it in my logs,
    and i've fixed too many space invaders to recall what it was (was
    probably 5 years ago now), the closest fault i have logged points to
    IC15 on the rom board, 74ls86.

    enjoy.

    Andy Welburn
    www.andysarcade.net

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    Sent via Gamer Newsgroups
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  7. Archived from groups: rec.games.video.arcade.collecting (More info?)

    On Fri, 22 Jul 2005 17:58:35 GMT, Andy Welburn <warlords@punkass.com>
    wrote:

    >I have seen this problem before, but i don't seem to have it in my logs,
    >and i've fixed too many space invaders to recall what it was (was
    >probably 5 years ago now), the closest fault i have logged points to
    >IC15 on the rom board, 74ls86.

    Ta - IC15 was the first one I checked - even swapped it out but to no
    avail. Have also, out of desperation, now also swapped out all three
    LS83's and the other three LS86's. Still the same fault.

    It's damned peculiar and very frustrating.
  8. Archived from groups: rec.games.video.arcade.collecting (More info?)

    On Thu, 21 Jul 2005 21:49:27 GMT, max-man@hotmail.com (max-man) wrote:

    Well, finally managed to fix it - the fault was in the LS157 at
    location 2A (IC20 on a Taito ROM board).
  9. Archived from groups: rec.games.video.arcade.collecting (More info?)

    The only other fault i had once where i was getting some things upside
    down and some things the right way up, it was a fault on the top board,
    in the FLIP circuit, it was for some reason pulsing on the screen flip
    line very accurately repeatedly per frame, causing some things to be
    upside down, some things the right way up. A very cool fault and very
    hard to figure out how the gates inside the ttl fail to cause that :)

    I would like to say, before you interject, that i have also experienced
    these kinds of problems where swapping the rom board appears to move the
    problem, when in actual fact, its the top board that is faulty, and for
    some reason liking some rom boards, and not others, only showing the
    fault with one particular rom board...

    Also, check and double-triple check your 480khz, 680khz or whatever kz
    timing signals go to the top board for the sound circuits, i've had
    failures in the Extend noise that have fed back on the timing chain
    causing mayhem on the rom board.

    I also don't want to point out the obvious, but check all the signals on
    the chips you've replaced with a scope and make sure your work is good,
    i know its not often that you can inadvertantly bust a track, short some
    tracks, etc, but it happens.

    One very last thing (honest) is to make sure you are replacing
    like-for-like TTL chips, ie LS for LS, S for S, plain for plain... there
    are some close tolerances and timings going on on the rom board where
    correct flavours of TTL are critical.

    Failing all else, i have some moon base boards, and millions of taito
    boards if you get stuck. I fix so many space invaders, it makes it
    interesting (for me, in a weird geeky way) to find one that isn't
    playing ball, i stopped making logs of my repairs a long time ago
    because i got to the stage where (i think at least) i know the circuits
    almost inside out, and most repairs i was doing were on what i deem now
    to be very simple things, mainly probably due to familiarity with the
    circuits.

    Andy Welburn
    www.andysarcade.net


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

    On Fri, 22 Jul 2005 22:13:31 GMT, Andy Welburn <warlords@punkass.com>
    wrote:

    >The only other fault i had once where i was getting some things upside
    >down and some things the right way up, it was a fault on the top board,
    >in the FLIP circuit, it was for some reason pulsing on the screen flip
    >line very accurately repeatedly per frame, causing some things to be
    >upside down, some things the right way up. A very cool fault and very
    >hard to figure out how the gates inside the ttl fail to cause that :)

    What a weird fault! Well, as you've no doubt seen, the fault in my
    case was indeed on my ROM board. At least it's fixed now - strange
    thing is that I could swear that I tested that LS157 early on when
    diagnosing the fault ............

    Cheers for all the details on your fixes - interesting stuff.
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