Plays, but no background stars

Original Gallag arcade game circuit boardset from 1982.  This board boots up and plays with good sound, but is missing its background stars. We have done no troubleshooting, certainly playable as-is, but we believe the stars should be present.

Boardset is sold as-is, see pictures for more details on its condition. 

Year 1982
Related Game Title Gallag
Quick Game Facts
Coin-Op Technical Details
Year: 1982
Manufacturer: Unknown
Genre: Shooter
Players: 2P
Conversion Class: unique
Orientation: Vertical
Monitor Resolution: CGA