Before cutting out wires, lets make sure the output levels are like we want them to be... I used my voltmeter to verify input and output levels. The batteries were giving 4.5 Volts (3 * 1.5v), and I expected to get the same at the buzzer. So I hooked up the voltmeter at the speaker wires and got a reading 0V. I Pressed the button and got a nice 2 second pulse of 4.5V and then it lower back to 0V.
Having tested the input and output levels, I cut out the battery source from the chime. I do not intend to have to change batteries in my computer for it to start up. This said, it would have worked, but since there is a better way, why should I bother?
Using an alternate AT power supply, I temporarily connected the former battery wires to the GND and 5V of the molex connector. the wire that was on the batteries "-" goes to a black wire on the molex connector, and the one that was on the batteries "+" on the red wire of the molex. When I turned on the power supply the circuit didn't melt and pressing the button I got a nice 2 second 5V burst at the buzzer.
Power Supply Molex Connector.
Connections for the power supply.
Since the output is a 5V, then a 5V relay is what's going to replace the buzzer. For those who don't understand what a relay is for, let's figure a switch, but controlled by an electric coil. You power the coil, the switch is ON. when the coil is not powered, then the switch if OFF.
There are lots of different relays out there, all have a coil, but not always placed at the same place. Since the surplus store I got it from could not give me schematics, I searched the web and went out with this one:
Now what we intend to do with the relay is make it function like a momentary switch for the power button. Reading the output with the multi-meter I found out what was the + and - on the speaker wires, and connected properly on the relay. Then I tried the button. You could hear the relay buzzing for a 2 sec. burst and let go. Verifying the switched contacts with the multi-meter's continuity (set to ring) I had a closed circuit for that 2 seconds burst. We will be wiring the relay to connect in parallel with the existing power switch.
Relay wiring Diagram.