The jacks are the header pins and the foil is referring to the traces. The sound board was notorious for flexing when the connector from the ROM board was attached. This flexing would cause cracks in the traces near the header.
You can put the logic probe on the individual connector pins (when the cable is attached to the ROM board and watch the lines pulse when the sound test (in the game diagnostics) is running. If you press the reset button on the sound card a single sound will be produced, but the lines on the input connector (from the ROM card) will not fire.
The other place to check with a logic probe is the output pins from the PIA to the D/A converter. If you are not seeing the data lines pulsing when sounds are supposed to be playing, try replacing the PIA. If you are seeing the output lines pulsing, check the input line to the amp with a scope or a very fast voltmeter. If there is a signal ther, then try replacing the amp chip.
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