Static Garbage, Dead Address/Data Lines and Failed Reset

Repair Case Summary

This page documents a firsthand Static Garbage, Dead Address/Data Lines and Failed Reset repair case. It is intended for technicians and collectors troubleshooting original Pac-Man or Ms. Pac-Man arcade PCB hardware.

• Date: 2019-08-19
• Board: Original Pac-Man PCB
• Category: Reset circuit / boot failure
• Symptoms:
  • Static garbage displayed in blocks with large horizontal spaces between them.
  • Z80 data and address lines were dead with no signal.
  • Reset function was not working.
  • Temporarily applying a high signal to Z80 pin 26 allowed the game to boot and run, although display problems remained.
• Diagnostic observations / tests:
  • Reset circuit was traced.
  • 9C and 7L showed abnormal signals.
  • 9C was replaced first, but the problem remained.
  • After other reset-circuit components were ruled out, 7L was replaced and the board booted.
• Components / locations investigated: Z80 pin 26, 9C, 7L, 74LS02
• Root cause: Bad 74LS02 at 7L in the reset circuit.
• Repair: Replaced the 74LS02 at 7L.
• Result: The board booted and played; a separate graphical fault remained and was repaired in the following entry.
• Repair note: Linked repair: the same PCB had a remaining graphics fault documented in the next 2019-08-19 record.
• Search terms: Pac-Man reset failure; static garbage blocks; dead address lines; dead data lines; Z80 pin 26; 7L; 74LS02; 9C; no boot
• Evidence: Physically verified repair / firsthand repair log

Related Repair on the Same PCB

After this reset-circuit repair, the same board still had a separate graphics problem. See Pac-Man partial maze with horizontal dead spaces — D2115 at 2A.

Related Pac-Man / Ms. Pac-Man Repair Cases

• Partial Maze With Large Horizontal Dead Spaces
• Dead Board With BAD ROM 0 in Test Mode
• Static Garbage Screen Caused by Z80 Socket
• Screen Full of Zeros With Irregular Black Blocks

How to Use This Repair Record

This is a firsthand physical repair case. The same symptom on another Pac-Man or Ms. Pac-Man PCB can have a different electrical cause. Use the documented diagnostic observations and tests to guide troubleshooting rather than replacing a component solely because it repaired this board.

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