Galaxian (Midway) PCB repairs
Tools: soldering iron, solder wick
Problem: Garbage on the screen - a mesh of horizontal and
vertical lines with a few random alien sprites
The legs of the RAM at location 1-P were broken off in the
socket, and the IC was missing.. I desoldered the socket and put in a new
one. No change when the board was powered. Touching the tops of different
chips, 5-K was really hot. It is a 74LS245. This one was already socketed.
When I removed the chip I noticed it was in the socket backwards. No wonder
it was getting hot! A new chip was installed and the board was fixed.
NOTE: The chip at 5-K looked as though it was installed correctly,
but the correct orientation was with pin 1 in the opposite direction of
the chip next to it. Always check the notch on the chip and match it to
the socket when installing it.
- Fix socket and install RAM at location 1-P
- Remove and correctly install a new 74LS245 at location 5-K
Problem: Game plays but no sync
Solution: Replace bad 74LS08 at 64
Problem: Game plays, screen looks smeared, enemies are red blobs
Solution: Replace bad 2101 Ram at 4F
Problem: Game keeps resetting, test mode shows bad rom
Replacing the rom board made little difference. The sockets had
been replaced on the main board before with cheap single wipe sockets, so I put
in a new set of dual-wipe sockets, replaced the rom board and it fired right up.
Solution: Replace bad sockets at 7F and 7J
Problem: Color on the Flagship was OK during attract mode, but
during game play it was red instead of yellow.
I figured this was a ram problem
so I started swapping the 93421 rams in row 1. Changing them out one at a time
and testing the board again, I finally replaced them all and still no change.
I decided to check the character roms. When I reseated the 2716 character eprom at 1K/L and the problem was cured.
Solution: Bad/dirty connection on eprom 1K/L, a 2716 character eprom
Problem: Dead board
Board was completely dead. No signs of life. First I checked the
crystal for a pulse with my logic probe and got nothing. Looking at the schematics
I found that the LS368 at 1E is in the clock circuit next to the crystal. I've usually
found that if the crystal does not have any broken connections, the chip that the crystal
feeds is stuck either high or low killing the output of the crystal. This was the case
here. I replace the LS368 with a new chip and the board came back to life.
Solution: Bad 74LS368 at 1E
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