Bench-testing a -133 MPU: swap the R113 diode for a resistor
The -133 version of the MPU (Granny and the Gators, Baby Pac-Man, Grand Slam) has a 1N4148 diode where R113 normally sits. For bench testing with the fixture described here, temporarily fit a 2k resistor in that position instead.
Systems
Games
Related tips
- Converting a -133 MPU to a -35
- Convert a -35 MPU to a -133 for Baby Pac-Man and similar games
- Still no seventh flash with F4 good
- Bally-35 MPU: remove the on-board rechargeable battery before it leaks
- MPU boots only some of the time
- MPU LED locked on with no flicker: likely causes
- Testing the MPU reset circuit at U9 pin 40
- Single reset parts that hold the LED on
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Two, Clay Harrell (pinrepair.com)