CAT M100D (S/N 3CJ00723) 72V

Truck originally stopped working, with fault code F6 displayed.

Found a badly corroded pin connector on the logic board. Repaired that & the truck worked fine.

Came back to it the next day and fault code F3 on display.

Checked & cleaned all connections to logic board again, all seemed OK.

Checked transistors behind board. Drive pair measured OK.

One hydraulic transistor was open circuit and the second gave voltage & resistance readings completely dissimilar to the drive pair.

Ordered & fitted a pair of transistors to the hydraulic circuit but the F3 fault code remains and the truck is still without hydraulics or drive.

Any guidance good people?

Thank you.