If you know the I/O port address, or the memory address (whichever applies) for the buzzer, a machine code program running in RAM should be able to produce sound from it.
This assumes that it was the intention that the buzzer would be driven by software.
When looking at the photos yesterday, I was wondering why a 16k byte RAM extension needed a 74LS74 (dual D-type pos.-edge-triggered flip-flops) chip. As these are not normally required. But one half could provide part of the circuitry for a one bit output interface, suitable for a buzzer…
I’ve not studied the PCB tracks, so normal Del Boy exclusions apply…
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