Atari Gauntlet 2 arcade pcb repair
Board showed missing graphics on the title screen and blocks in game were often wrong.
After some diagnosis it became clear the scroll position on the tilemap was wrong – rather than actually anything wrong with the tilemap itself. The missing title screen graphics were instead horizontally scrolled off screen by 256 pixels.
The scroll position is controlled by the 137419-104 custom chip and this seems to have failed with the 256H line stuck high. Fortunately this chip is also on a few other Atari games, including Pit Fighter, so I pulled a chip from a corroded parts board to fix the Gauntlet.
The board had another fault I recognised immediately from another repair – sprites with ‘sparkly’ vertical lines down the screen. This is a failure of the resistor packs used to pull the sprite data lines high when erasing a scanline. These packs are at the corner of the board, so any flexing of the board can lead to hairline fractures. 470ohm resistors can be used as a replacement.