Hello Mac:
The "Safety Charge Pump" is a device for reading a 5Khz signal produced by Mach3, and activating a relay. You cannot see this signal with a voltmeter.
The Mach3 program generates the 5Khz. signal when it is in active control. The charge pump board reads this signal, and then activates a relay, which in turn supplies +5v. to the "enable" pin on the machine driver amplifiers.
The reason for the charge pump is to prevent unwanted machine activity before Mach3 is active/in control. If power is sent to the hardware i.e., drivers, spindle etc., before Mach3 is in control or even ON for that matter, the machine axis motors, or the spindle could become energized and create a dangerous situation.
You can buy a standalone charge pump board from "CNC4PC". They have a diagram how to wire it properly. Many BOB's have a charge pump already built in, and utilize the signal without a separate board.
The 5Khz. signal is output on the Pokeys board on pin #53. Run a wire from pin 53, to the input terminal of the Charge Pump. The charge pump board has an input for +5v. and GND from your 5v. Power supply. The board has a relay, with one N.C. terminal, one Common, and on N.O. terminal. Wire +5v. from the Power supply to the Com. terminal, and a wire from the N.O. terminal to your "Enable pin" on the drivers. When the Charge pump gets the 5Khz. signal from the Pokeys pin #53, the relay will go active, and send +5v. from the N.O. output pin, to the Enable pins of the drivers.
Do not draw any power from the Pokeys board for the +5v., only from the Power supply; attempting to draw power from a Pokeys output pin will damage the device. The Pokeys board is not designed to supply DC power from the output pins.
When Mach3 is "ON" or active, the Charge pump will turn on the relay, and also show a red LED on as a visible indicator. Likewise, when you shut-down Mach3, the Charge pump relay will drop out, and the drivers will become inactivated.
John