Game play is fine.. just no sound. Volume works. You can hear the amp waves get high and lower when turning volume dial.
In my experience.. start with the RAM on the board, the MC6810 those seem to have an uncanny ability to die also the 6821's go bad.
Also just check the soundboard isn't missing the 3.58MHz crystal, those also get knocked off the board.
Also check to see that the correct sound ROM in on the board and it's strapped correctly for the EPROM type.
But put the sinistar into test mode, get into the sound test and set the auto up/down switch and it'll step through each sound line. Put a logic probe on the IC10 (6821) pins 10 through 14, you should see pulsing as it goes through the sounds. Also put a probe on pin 18 as that should pulse each time the CPU outputs a sound to the sounboard.
If those aren't pulsing, check the inputs on IC5, see if you are getting pulsing there, but not on the outputs would be bad IC5 ( haven't seen one of those go bad ), if there's nothing on the inputs it's most likey the 6821 on the ROM board.
So if the inputs are all good, then put a probe on pins 2 through 9, those pulse when a sound is being played, it's output to the DAC.
If those are pulsing check/replace the DAC at IC13 and transistor Q2, I've seen Q2 physically knocked off a board before (!)
If there is no output from the 6821 to the DAC, then swap the RAM, 6821 and CPU in that order.
- James