AXBB charge pump fault

[john swift]

yes
that's the resistor



unless the FET has gone low resistance between the gate & source

the voltage across the 10K resistor should be the same as the voltage across the FET gate & source

as the static FET gate current is virtually zero ( leakage current 100 nA )
the volt drop you measure across the 220 ohm will be zero

you will find the via (plated through hole ) in the copper trace connecting the 10K resistor and FET source is the – 24V supply - making it an easy test point

with a damaged FET
a fault current with the relay connected could leak out of the gate and alter the gate voltage you measure


John

PS

the FET was replaced by the original part

NTR5198NL from FARNELL

https://uk.farnell.com/on-semiconduc...ngdom%2Fsearch