[SiriusHardware]

Attached, a snippet from the same diagram we used when looking at the keyboard problem, only this is the upper half and it shows the user port and its connections to the 'other' 6520 - the one which is not used for the keyboard.

If you want to be sure you are using the right contacts on the user port, use your meter-fu to check which of the user port pins is directly connected (zero ohms) to pin 19 of the second 6520. That user port connection will be 'M'/CB2.

You can use any user port pin which is directly connected to 0V as the return connection, but 'N' will be the most convenient as it is next to 'M'. Again, use your meter to check that the user port connection you believe to be 'N' is directly connected (zero ohms) to any known 0V point.

We need a little more info about the sounder / buzzer you are trying to use, either a link to where you bought it from or, if it's one you already had, a few clear images.

The diagram shows CB2 coming directly from the CB2 pin (pin 19) of the second 6520 and if that's true the CB2 pin alone will not have enough strength to drive a low or medium impedance speaker. It may be able to drive a high impedance transducer such as a passive piezo sounder, although there are potential pitfalls when using those too.

Let us know what sort of sounder you actually have.