How the control board drives the displays
RIOT U5 puts a 4-bit count on PA0-PA3, which Z25 decodes into 16 digit strobes. Segment data leaves as three groups (A, B and C) of eight lines, each latched by one of three 74175 chips clocked by PA4, PA5 and PA6.
Systems
Related tips
- All displays are dark
- Display data in attract mode
- Control board display connectors A1-J2 and A1-J3
- A display segment or digit is always on or always off
- Status display is off but the score displays work
- System 80 control board chips
- How the control board reset circuit works
- Control board power-on checks
Source: System 80 Service Manual, Gottlieb