Im not familiar with the machine but attract mode is controlled by the CPU.
We can get some clues as to what's going on here.

Gorgar has sound, so im assuming that it has some Dip Switch settings on the MPU that allow " attract with sound" .. " attract without sound"  etc. Try changing this setting and see if it makes any difference......

Also, does the game function properly when performing all the self tests?

Are you 100% positive that it works properly when playing?