Yes, changing error codes usually means poor connections somewhere. Either corroded chip legs, bad chip sockets, or loose or misaligned connection at the interconnect board. You should remove all the socketed chips in column 3 and 4 on the cpu board (where the 10XX custom chips are), clean the chip legs, and reseat.
If you aren't careful, the chips legs can be corroded to the point where they break off, and then you have a much more difficult repair. If you clean and reseat the chips and still have an issue, it's possible that the sockets are just bad also. On most repairs these days I usually replace all the sockets in column 3 and 4, which are the program roms responsible for the game booting and running.