Checking the PIA outputs with the test EPROM

Steps

• Once the test LED flashes, power off and fit both 6821 PIAs at U10 and U11. The board LED should now flash in step with the test LED but opposite to it.
• Re-wire the test LED: LED leg to +5 V (TP5), resistor end used as the probe.
• Touch each PIA pin 2-17: the LED should turn on and off every second.
• Pins 19 and 39 should alternate the same way.
• Pins 26-33 are data lines and should pulse on a logic probe.

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
• U9 signals with the test EPROM running
• 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

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