oh, i will give you some credit there darren, but thats only after i starting looking farther down the line!
Galaxian Repair #2 was even more fun!
symptoms: DEAD
dumped roms, checked with rom ident, recorded the Fluke Sigs.
pulled out the fluke, z80 pod, connected it up, RAM, OBJ_RAM, VID_RAM tested fine, but no go on roms, replaced those pesky sockets, retest, good to go.
still no video... ok, check the V/H Counters, there working OK.... then just worked down the line, looked like everything was working OK, but just no video.
Turns out the /6mhz clock was being shunted to ground, so swapped out the 7404 (schematics show 74386?) still shunted.. so pulled out the leak seaker... found it to be the input pin on 1U, installed socket, new chip, wala! video, but no star field... hunting around the star field logic, found a broken trace, so fixed it, and all is good!
the romsets on these were wierd, the had the 1 h/k/j/l roms from Galaxian, and u/v/w/y/z from Galaxian Hack 4 ? but not the hjkl roms from Glaxian hack 4.
other board had war of bugs
http://www.youtube.com/watch?v=KDQSuqm4Si0