AXBB charge pump fault

[john swift]

It is not easy to tell what the problem was

a case of no fault found that could of damaged the FET

As the relay worked when the wire from the AXBB output was connected to the -24V supply

you can only suspect either there was an intermittent short connecting the +24V supply to the AXBB output
or
an intermittent open circuit that generated a sustained back emf that over stressed the diode in side of the NTR5198NL-D FET

or may be it was a faulty FET

John

PS

the diode added across the relay coil and a 27ohm resistor in series with the relay coil
will help to protect the AXBB output

the resistor limiting the current if coil is short circuited
and the diode clamping the back emf when the relay is switched off