Fixed: Ms Pacman Bootleg

[grobda]

Had what i thought was a pacman boot for years, decided to have a fiddle with it;

screen split and game playing double speed;

had a google (sited listed below), found 74161s were a possible culprit, probed the 161s in the corner of the board and found an output stuck high. piggybacked a pulled chip;

sorted. turns out its a she

sites used;

http://lawnmowerman.rotheblog.com/#playsbut

http://www.arcadegameover.com/pactrouble.html

http://www.mikesarcade.com/arcade/repairs/mspacman.html

 

[DanP]

Nice fix dewd, thanks for sharing

Dan

 

[grobda]

had to share i was amazed i actually fixed something

got alpha mission and a galaxian back up and running after that (just simple things like reseating roms).

the ms. pac still has an issue with video ground, same with any of my pcbs that dont have a specific ground pin for the video.

they get horizontal blur on leading edges - stuff like text and fine lines - the pacman maze shows it best. same problem occurs in the cab so its not just my test rig. any tips on eliminating this?

i thought it was shoddy bootleg wiring but alpha mission does it too and its an original.

 

[andyman]

Have you tried linking video gnd to power gnd ?

Congrats btw dude, love Alpha mission

Andy

 

[grobda]

Have you tried linking video gnd to power gnd ?

Congrats btw dude, love Alpha mission

Andy

the shots from the ms pac are with vid ground to common ground. (by a link on the jamma adaptor) certainly better than no video ground but not as good as with a separate video ground.

results in mushiness with fine vertical lines - examples below, 1st is the ms pac 2nd is pacman on galaxian hardware (original board with separate video ground)

pardon my crappy camera is doesnt like closeups but you can see that the lines of the maze that are 1 pixel wide are clear horizontal and faint vertical on the ms pac. the whole picture is like this and all colours are affected. cab with a mtc9000 monitor does the same thing, if anything its worse.

 

[trm]

That could be caused by the tightness of the timing in the video stage, or more likely the "resolution" of the game's video. If you have a game which has a resolution of 320x240, then the horizontal width of a vertical line will be thinner and appear sharper than a game which is 200x320 because they're being displayed on a screen which has a fixed horizontal resolution.

 

[grobda]

dont think its resolution related. heres a pic of alpha mission to show it better;

its like each scanline is blurred and drags the pixels wider than they should be, most preavalent where there are blocks of contrast ie text/lines. pcbs with a proper video ground are fine.

 

[trm]

Will have a look at what MAWS thinks the games' resolutions are to see if that can be ruled out. Can you give an example of another game which doesn't exhibit the problem?

I assume this is straight into a CGA CRT and no upscanners/switchers anywhere in path?

cheers

ps Nice Ms Pac fix too btw.

 

[grobda]

ive just tried raiden 2, galaxian, air raid and they're all crisp with none of this blurring/streaking. never noticed anything with the 20 or so other boards i have. the other one that does it is rambo (ikari warriors bootleg) with the same snk pinout as alpha mission.