Erratic flashing counter's dots on Recel sys3

Counter's leds

On a Recel System 3, each counter has four LEDs: 

• SELECT is at the top right of a counter to indicate that a game for this counter is in progress. 
• UP is at the bottom right of a table and indicates that this counter is in progress (ball in play). 
• 1,000,000 is located on the left of a counter. It lights up when the 1,000,000 point limit is exceeded. 
• The fourth LED is actually the control circuit for the decimal points (DP) of each 7-segment digit. They all work together for a given counter, except that if a 7-segment is off (value equal to F), then its corresponding DP will also be off. 

To manage this 1-by-1 extension of the DPs, there is the A3 circuit on the Display Board. A3 is an 8-input NAND logic gate (SN7430). After 50 years, this gate is often faulty. It is usually the cause of these strange flashes that are not synchronised with anything. 

Another typical symptom is what you can see on the illustration picture above : During the pinball startup sequence, you will observe lighten DPs on all 7-digits of all counter's including those which are off (value F) ; or vice- versa.

Replace this IC, and everything should be back to normal.