As many of you might know, Galaga presents some interesting headaches due to it being a multi-processor board, and sometimes the 74LS367's that interface the three processors to the system address bus can have problems. How to find the problem is where this trick lies. Get yourself a Z80 NOP and plug it into the Z80 socket for each of the three Z80's - one at a time. Now you can check the buffered address bus with ease at the pull-up resistors,finding any bad connections or bad 376's very quickly. I made up a Z80 NOP a few years ago, this has a Z80 CPU with the data legs, reset, NMI, Halt legs all bent up and over the top of the CPU, then you tie the DATA lines to NOP (00 I think), and the CPU controls to high with a pull-up resistor. Make a simple Reset circuit with a diode, capacitor and resistor so the Z80-NOP will ignore the board and away you go! This works for most processors by the way...some more info on NOPs is on http://www.spies.com/arcade I think where Al archived some of my notes... John :-#)# John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) http://www.flippers.com "Old pinballers never die, they just flip out." To UNSUBSCRIBE from techtoolslist, send a message with "UNSUBSCRIBE" in the message body to: techtoolslist-request@flippers.com. Please direct other questions, comments, or problems to jrr@flippers.com.