Quoted from Quench:No. The outputs can be on either side of the chips - the chip datasheets will usually describe them at varying degrees.
In sound test mode you want to see that the sound board is receiving commands from the MPU board and traversing them through to the tone selection circuit of the sound board.
So in sound test mode, you want to check that you're getting pulse activity on your logic probe at input pins 4, 7, 13 and 14 of U2 and the trace between J1 pin 12 and resistor R30 - these are where sound (tone) select commands come from the MPU board. See the five lines in RED below.
These then get traversed to the lines shown in BLUE and should all indicate pulsing on your logic probe. See output pins 3, 9, 12 and 15 of U2.
From there they go through the U1 inverter chip and come out and onwards to the U3 PROM chip on input pins 10, 11, 12, 13 and 14 (see the lines in PINK below). Again, these should all be pulsing.
These U3 PROM inputs are used to select pre-programmed dividers for the tone section. If the outputs of the PROM (lines shown in GREEN) are not pulsing, you will always hear a single tone.
There's plenty there for you to check with your logic probe - hopefully you'll find the outputs of one of the chips mentioned above are stuck high or low (not pulsing) causing the board to be stuck on the same tone.
So the signal sequence is red to blue to pink to green.
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I'm busy restoring a Bally Playboy 1978. Have repaired everything but the sound card sounds a bit weird to me. It plays tunes but seems to be the same tone being used. Volume works and sustain works etc.
I followed the above and the inputs to U3 are all pulsing 0v to 5v except E pin 14 is about 3.8v all the time BUT it's outputs all seem to be stuck on about 0.4v I'm assuming this isn't right? If not where do you get that IC?
I have a video of the game/sound but not sure how to post video.