Repair Logs

Lunar Rescue (Taito) PCB repairs

08/14/2000

Tools: schematics, logic probe, soldering iron, solder wick, multi-meter

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.

Solution:

• 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