U6 select signals with the test EPROM

With the test EPROM in U6: pin 18 reads about 2.5 V without an adaptor (0 V with the 9316/2716 adaptor); pin 21 reads about 3.6 V without an adaptor (+5 V with it); pin 20 is ground with very short positive spikes that only a logic probe or scope will show.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• Using the test EPROM memory test
• Setting up an MPU for the test EPROM
• Making the test LED for the test EPROM
• Never use a TMS2716 EPROM
• Which EPROM format to burn
• Mod1: two 2716 EPROMs at U2 and U6 on a -17 or M-100
• Test EPROM: the least an MPU needs to run it
• After the test EPROM: refit the game ROM and count flashes

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Two, Clay Harrell (pinrepair.com)