this trace to mix speech in with the SB300 sounds is present on later boards. If the board is original to F2K it should have the trace, but worth checking for trace or the wire.

The lamp interrupt (aka speech busy) signal that comes in MPU j4 should also change state when the speech. I think it normally sits low when no speech happens and goes high when speech is playing.

Do you get silence when speech should be playing? Like when you begin the game there should be (speech) or silence and the lamp int should go high during that time.

I don't think there is any speech in solenoid test mode but I am not 100% sure on that.

If lamp int never goes high the speech processor is probably not working because its bad or some other kind of problem like at U6, U5, U4, U3, U2, or input connectors. You can probably work through some of these circuits like U5 and U4 Q pins should be pulsing when speech should be playing. U6 P9 should be low when speech is playing, U6 P10 should be high or pulsing when speech is playing. U5 P2 should be pulsing when speech is playing.

I would try a new speech processor chip but saddly they are pretty hard to come by. Another working speech card to compare to and borrow the working processor would help.

make sure lamp strobe 1 is reaching speech board U6 Pin 8. THere is a 20k series resistor on speech board. P8 should be pulsing i think at or around 120hz. If U6 P8 and P9 both pulse but P10 is always low U6 may be bad.

I am not 100% sure what to expect from the speech CPU and i don't have one on hand right now to check, but i'd expect the /BUSY (u6 p9) to only be low when the processor is playing speech and sit high when not doing speech, but maybe it pulses and then stays low when speech plays.

If the Q pins on U5 and U4 never pulse then I'd think the clock pin is never pulsing which is also done by U6 with lamp strobe 2 and PD2 / PD3 input.

Double check the input connectors, Lamp strobes and PA and PD inputs, otherwise U6 might be a good shot at being the problem. You can get the datasheet and work through the truth table for U6.

saving this one to the PC.

As someone that used to work in architectural / engineering printing and document management, I appreciate such a beautiful scan! It almost looks like a digital recreation.