Lunar Rescue (Taito) PCB repairs
Tools: schematics, logic probe, soldering iron, solder wick,
Problem: Board appears dead
First thing to check is if the CPU is running. No clock to Pin 15 on the CPU.
Looking at the bottom ROM board, I traced the crystal output to IC6, a 74160. The crystal
feeds a signal into pins 2 thru 6, only pin 2 was pulsing, 3-6 were all stuck high. I replaced
the chip with a socket and a new 74LS160. The inputs then started pulsing, but there was
still nothing on the screen. On the CPU board, there are 2 IC11's, they are both 74S241 chips.
They were so hot I burned my finger on them. I socketed both and installed new chips. Still
nothing. With the power on, I pressed down on the different eproms and noticed Rom 3 was in
a new socket, when I pressed down on the chip, then looked at the screen, the game was running.
Turning off the power and inspecting the rom socket, I noticed there was 2 bad traces on pins
1 and 2. The pads that the socket were supposed to be soldered to were missing on the bottom.
Jumpering pins to the proper places fixed the problem.
- Replaced 74160 at IC6 on ROM board
- Replaced 2 bad 74S241 chips on the CPU board
- Jumpered 2 traces on ROM 2 on the ROM board
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