Pinball Action - Tehkan: Graphics and sound problems! Help!

ftadeufs

n00b
Joined
Mar 18, 2019
Posts
26
Hello guys!

I have a board i got from a friend that I would like to repair to good working condition again. I´m trying to learn as much as I can about repairing boards and this is a good oportunity to practice more, and learn more, I hope...

It´s a Pinball Action from tehkan but it´s a bootleg. As far as I´ve seen by pictures over the internet is a 1:1 clone of the original board, but built cheaper.

I haven´t found any schematics and AFAIK they dont exist. Does anyone have any experience with theese boards or knows any documentation or repair logs that might help? What kind of stuff is in which ROM? They are all masked roms or OTP PROMS, and I can´t dump them with my TL866II plus.

The game runs, but the graphics are very weird. At first it was just alternate vertical lines (horizontal if the monitor is rotated 90º and the game is rotated), but now some graphics are gone. I have some spare RAM IC´s but I dont wat to start changing things like crazy. I want to learn how to do proper repair on arcade boards, regarding graphical issues with the sprites, etc. Where is the best place to start checking signals?

I have checked with the logic probe some data lines and address lines on both Z80´s and RAM ICs, and i´m a bit confused. Some of the chip enable lines are Low active and working fine, but some others are pulsing. I also have observed different behaviour of data lines according to different stages of the game.

I would appretiate some guidance over fixing this board if possible, please! :help:
 
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