The display voltages to check
Check six voltages: +60 V DC for the seven-digit displays' anodes and grids and +42 V DC for the four-digit status display, both from the power supply's high-voltage section (60 V AC rectified and regulated by Q1/Q2, with zener CR6 dropping +60 to +42 V); the filament AC windings on the small transformer (5 V AC for seven-digit, 3 V AC for four-digit); and the DC offsets on their centre taps (+8 V for seven-digit, made from +12 V by zener CR7 and R10; +5 V, the logic supply, for four-digit). The offsets reach the lightbox through A12J4.
The display supply runs at 60 to 69 volts; work on it with the game off and never plug or unplug display connectors with power on.
Systems
Related tips
- Measuring voltages on a display board
- System 80 schematics' 'offset' voltages are DC bias for the display filaments
- Meter check of the display board 7432
- Checking the +60 V filter caps on a display board
- Replacing a display glass tube
- How the System 80 fluorescent displays light
- Meter checks on a display tube
- Meter check of the UDN6118 display drivers
Source: Troubleshooting Gottlieb Displays (On Target technical newsletter, vol. 3 issue 7, 1982), Gottlieb "On Target"