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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
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.
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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