I have a Bally AS-32 sound board that has been rebuilt and brought back to life... sort of. The sounds are correct, all voltages check out, both pots have been replaced (X2), TIP29 regulator changed, capped, amp changed, speaker checked. It does not have a volume pot inside the coin door as I believe it should. The volume is low and I cannot get it turned up to an acceptable volume. What am I overlooking??