Quoted from Cheddar:I thought we had established this sound board works in another firepower. Is that correct?
Incorrect, No Sound Boards work. Originally an alternate FP sound board from a working(prior to going into storage)game placed into project machine, along with other boards as I move along in diagnosis of game issues. Once I saw I had power board issues, I swapped for another in order to continue tests, so I could order all needed parts from Ed in one try. With the alt power board in, game plays etc..but no sound at all. No speaker buzz, nada.
Quoted from G-P-E:Typo on my post -- should have been pins 5 and 6, not 4 and 5.
On sound board -- pins 5 and 6 are both connected together. That diagram uses pin 5 but could have just as easily used pin 6.
Solder tabs are not exposed for wires 15, 16 and 18 on that transformer so difficult to measure there. To see full voltage - measure between pins 1 and 9 on sound board with connector installed. To see tap voltages (half voltage) - measure between pins 5 and 1 for one tap and measure between pins 5 and 9 for second tap. However - since you measured +12 on TP1 and -12 on TP2 then there is nothing wrong with the AC voltage getting to the board and BR1 on your sound board is OK. And IC8 (7805 voltage regulator) is also working fine since you got 5V on TP4.
So... now what I don't see described... what is actually happening to the sound board? No sound at all?
If no sound, that is difficult to tell with just a meter. First place I would look is J4 connection to volume control but to do this really requires an oscilloscope. I would follow sound from connection near W1 through R11, R12 and wrapped around to C12 and see if the signal disappears or not.
Ed, I think you are saying that if I had something more than a MM and logic probe I might be able to work backwards on the sound board(not card) and find where the signal ends, Correct?
Quoted from barakandl:break the board into three section. the power supply (i think you have checked this is OK). The CPU. The analogue stuff.... check through in that order.
The CPU, see if reset is high (p40). external clock is going (p37). When you push the diag button the PIA ports connected to the DAC 1408 should begin to pulse. In game play mode the PIA ports going to the DAC should also go active when you trigger sounds.
Introduce noise through the amplifier to check to see if it is likely working. Just twizzling the pot if you get some cracks, pops, and hum is a pretty good sign. When the sound board is connected to the speech card the analogue sound first goes across the ribbon to mix in with speech and goes through the 1458 op amps then back across the ribbon again. A bad 1458 can produce no sound or speech.
Common issues... I see and AMI brand CPU chip in a possible scanbe socket. So you have an unreliable chip in an unreliable IC socket... double whammy.
The ribbon cable gets screwed up from the tight bends. It looks like you have the type you can attempt to press down a new ribbon into... last resort to do that... make sure you are sure the ribbon is broken before trying because it does not always end well.
Not uncommon for the 1458 op amps on the speech board to be blown.
B & I, That is a lot of great info, I think I read it slow 4 times and likely only got 70%. But I think you want me to look only at Sound board(not card) and break it down into it's 3 functions, then eliminate areas that appear to work(ie: power section.) The remaining 2 sections CPU and analog stuff don't jump out at me. There are a number of IC chips with 9 and 10 being the biggest and both look like 40 pins a piece, but that about it for my identification skills.
Let me share my latest, since I began to doubt if the 2nd sound board installed was still 100%. I went to a 3rd Sound board from a definitively working machine, my Black Knight. Right or wrong, I figured it was safe as it is same part # w different Roms and I just want to hear anything. Well, you've guessed it, nothing again. For all 3 boards installed I did press the lil test button and got more of the nada.
I know that my greenhorn experience level is way down in the cheap seats compared to you helpful 3, but I'm having a hard time buying it's a board issue. I know there are limited components left beyond the board down in cabinet, which seem easier/quicker to test. The original speaker did measure open, so I think it's bad. I do have an alternate 8ohm(measured 7.3) speaker alligator clipped in the cabinet with good continuity to board. The other component is the volume control, not sure how to test, but does have continuity back to sound board. I know this may be a folly to check off board, but 2 working boards installed is really messing with me.
Thanks for letting me express my frustration. I know it's difficult on your side fer sure and ultimately 4 heads are better than my one!
FP Sound B.pdf
Lodi, CA
But at least I know the only issue(s) are left on the board. I think there are some write ups that have recommended upgrades to this board, plus some of the usual suspects mentioned by you. My hope since I have limited diagnosis equipment, is to do a rebuild on the board with recommended replacements/sockets/upgrades/etc. Then......I should have a working board! Finding the failed component is important, but replacing it without the remaining weak links seems silly. So, I'll replace them all as they are reasonably affordable. Remember, I'm already going to do the power board. 
