If the drive circuit is producing a clean square wave, it's likely something beyond the driver board. Since this test uses a low frequency signal for testing, it's not definitive because the driver IC could be OK at low frequencies but not at the higher frequencies that are involved with the normal operation of the class D amp circuit.
To test the drive at higher frequencies, you'd have to inject a higher frequency signal into the 2113 but I've never had to do it on this board.
It's also possible that the circuit producing the high-side drive circuit supply voltage isn't working but that's not likely.
It's possible that there are leaky or weak drivers. To test them in the circuit, you'd have to find a way to break the connection to the output gate resistors so that they wouldn't not be driven. Then test as you did previously. Loading them with a 470-1k ohm resistor would make it more obvious if one was defective.
To test the drive at higher frequencies, you'd have to inject a higher frequency signal into the 2113 but I've never had to do it on this board.
It's also possible that the circuit producing the high-side drive circuit supply voltage isn't working but that's not likely.
It's possible that there are leaky or weak drivers. To test them in the circuit, you'd have to find a way to break the connection to the output gate resistors so that they wouldn't not be driven. Then test as you did previously. Loading them with a 470-1k ohm resistor would make it more obvious if one was defective.
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