Bally Doctor Who (Bally, 1992) No Sound

[SoInPin]

I have a Dr Who pinball that I purchased from an estate. Everything seems to be OK except that there is no sound. I sent the sound board to K's Arcade for rebuild/repair. Still, no sound. I thought the speakers might be bad, replaced those. Still, no sound. Not sure where to go next. Any ideas or has anyone experienced this with their Dr Who machine?
Thanks

 

[pinballdaveh]

the audio board output is a 2 wire 3 speaker system hooked up in a series parallel config. the speaker output connections are J504 pin3 black wire and J505 pin2 black-yellow wire. both of these jacks look to be 4 pin connectors with no key pins , so installing them in reverse is possible. verify that the correct plugs are plugged into the correct jacks. there is also an inline connector from the head speakers to the cabinet speaker , check that this connector is connected. i dont see a ext. volume control , so no need for that worry. unplugging the 2 speaker wire jacks and doing a resistance test on the speakers looks to be 9 ohms