Odd, unexplained CPU behaviour, memory errors or RAM failures on games made before Ice Fever.
Random errors on early System 80/80A CPU boards: add the R/W pull-up
Cause: Gottlieb overloaded the 6502 R/W line. From Ice Fever on they fitted a pull-up resistor on the watchdog (reset) board plugged into TC1; boards without it have no pull-up.
Checks
- Look on the solder side for a resistor between TC1 pins 7 and 11.
Fix
- On the solder side, bridge TC1 pins 7 and 11 with a 3.3K resistor. The reset board itself is not required.
Systems
Related tips
- System 80 and 80A CPU boards swap only with the matching U2/U3
- Swapping CPU boards between System 80, 80A and 80B
- Which System 80 CPU board goes with which games
- System 80 CPU board main chips
- Reading the System 80 CPU DIP switches
- A System 80 board boots without its 5101 RAM
- U2/U3 rules ROMs decide which system a CPU board runs
- System 80 CPU board revisions D102, D107 and D20869
Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part Two, Clay Harrell (pinrepair.com)