I had this buried in another post with numerous other problems (already fixed) on my F14. I did a lot of diagnosis tonight and could use some tips to finish repairing. I think I'm close -- here is what I know (and hopefully this will help others with a similar problem in the future)

0) Almost every cap and resistor tested in circuit and verified with a good board, nothing out of spec.
1) Another sound board (from a Whirlwind) with F14 roms works perfectly in the game, therefore the cable, speaker, volume are NOT the problem.
2) New roms in place.
3) Sounds 1-9 (speech) from the CPU work perfectly when fed through the mixer on the sound board.
4) Disconnecting that cable, there is still speaker humm so amps are working fine (and vary when touching various points in the analog section)
5) The logic probe shows the incoming data PB0..PB3 (pins 10-13) on the 6821 PIA (U2) pulsing correctly during sound music test; again data making it from CPU to sound board fine.
6) There is NO output on the PIA on the D0-D7 data lines. Also the ( E ) pin 25 is stuck low and not pulsing.
7) Therefore, testing U6 (74LS74) showed all pins solid (no pulsing) even though it's right past the oscillator (CR1). Pulled the chip and replaced with socket. With the chip not in place, 6 pins went dead (x's below), other pins stayed the same as when the chip was in place. Replaced with different 74LS74, still no pulsing.

1 H 14 H
2 H x 13 H
3 L 12 L x
4 H 11 L
5 L x 10 H
6 H x 9 L x
7 L 8 H x

8 ) Also checked U13 (74LS04) that is connected to the crystal. That one is pulsing.

Therefore, I believe that CR1, the 8 Mhz oscillator is dead. Does this make sense given what I have found? I am doing this with a cheap 80's Radio Shack logic probe. However when testing the ( E ) lines (pin 25) on the 6821 PIA's on the CPU board I did have pulsing there, so would have expected the same thing on the sound board.

I have to scavenge some old videogame boards and see if I have one to pull and try out, but wanted to see if it seemed like the right track given the diagnosis? Thanks for any tech confirmation!

IT'S FIXED!!! It was the CR1 8.0000 Mhz oscilator!

Found one on another board, swapped and IT WORKS! Wish I had done that before the 14 pin socket, but oh well, it's fixed.

So before anyone goes and replaces 40 pin PIA's, 14 pin 7474's or replacing caps and what not when a System 11 is lacking background music, test for pulsing off the CR1 oscilator. That MAY be the problem.