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Last days i fixed a few of the -really- old boards, Galaxian, Pac-Man, Missile Command...
I must say those boards looks very primitive (because they are very primitive) and the schematic is on the same level. Not my favorites...

However, this particular Galaxian - Midway had some funny issues i want to share.
I started by modifying the board for DC - Jamma supply.
After first boot attempt i got nothing. Reset and clock checked. Clock missing. Noticed that 1E ( LS368) already had a socket installed. IC checked - it fails. Replaced, clock present, reset present, some garbage on screen.
Tried the test ROM without sub ROM board. Some scrambled letters pop up instead of clear text. 1K/1J ROM issues? Checked the address lines, A3 found stuck LOW. Measured with GND, it was shorted. ROM removed, still shorted, so 3J - LS157 was replaced.
At this point i got clear text with ORAM STUFFED.
ORAM checked, i did not rush to de-solder it - some address lines were looking funny.
4E/5E checked, and since i already had an issue with this type of LS157, i verified if some pins were shorted. Yes, pin 9 at 4E was shorted to GND. Replaced.
Now, i have no more ORAM error but a reset just before the crosshatch. Still. some signals were not looking good on 4F/4F - even if the test ROM shows OK on ORAM.
Decided to pull out 5F as well (same type of LS157) and it fails during test (no short circuit on this one). Funny that Test ROM reports all OK.
Chip replaced, and now i was in the same reset at crosshatch. For i second i could see BAD ROM message. Checked all ROM from sub board, they checked ok in MAME but looks funny - like IREM version of Galaxian.
Replaced the sub ROM board with a known working one and yes, game boots and runs fine.

I finally replaced all LS157 on this board- that particular type, in order to prevent future failures. As far as i know, the manufacturer was PHILIPS (It`s SIGNETICS, thanks Sam for info)
Board tested for 24 hours - all good.
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