Data East Desert Assault arcade pcb repair
Game booted to a solid green screen or sometimes would not boot at all.
The first fix was simple – the ROM sockets and ROM legs were very dirty and oxidised. 1200 grit sandpaper on the ROM legs and Deoxit in the sockets cleaned things up enough that it would boot consistently.
The next fault was a real headscratcher – in the attract mode the screen wouldn’t scroll – the characters just ran to the right hand side and got stuck. Starting a game had a similar fault. This was clearly a program logic error – however the ROMs had tested good, and it was likely the RAM was good as well (piggybacking known good RAM made no difference).
The fault didn’t become clear until I started swapping the top and bottom boards with a few other working Desert Assaults. Desert Assault is a dual CPU game, with a 68000 on each board and in this case the top board had a different revision of the program than the bottom board. Someone must have tried to repair the board in the past with fresh ROMs but only replaced the top set (bottom set was still original). Reburning the top ROMs fixed the fault.