AXBB charge pump fault

[john swift]

Hi Charlie

I am surprised the the charge pump output has failed again

I would of thought the combination of the diode added across the relay coil to control the back emf
and the 27 ohm resistor to limit the current if the relay was ever short circuited
would of protected the FET

Can you measure the voltage between the CHP O1 and -24V terminal

when the output should be ON and OFF

and if possible the voltage across the 10K resistor on the PCB

knowing the voltage between the 74HC14 GND pin 7 and output from pin 2
will help

I would expect it to be 0V when OFF and +3 to +5V when ON

from the FET data
Gate Threshold Voltage = min 1.5V to max 2.5 V

John