My Experience

Heres the solution for Nokia E73 mode with a not working  joystick problem.
If encountered a non responsive joystick on nokia E73, this solution may help fix and repair the problem.
The joystick on Nokia E73 is being mounted on the Keypad Flex cable matrix. You may need to disassemble the device carefully. After being successfully disassembled, check the whole keypad flex for possible damaged. Check and clean the optical joystick lens and the module assembly, see the picture below..
If the keypad flex is already damaged you may need to replace or install a new replacement spare.
But if the keypad flex matrix and the optical joystick seems both okay or already tried installing a new replacement keypad flex, but still the joystick doesnt work. You may then proceed to the hardware troubleshooting procedure below.

See the solution below and check the two supply voltage that feeds to to the optical joystick module to determine possible causes.You may need to check and trace these supply voltages for further troubleshooting.
There are two 3D accelerometer chips that controls the joystick movement. If these two chips became damaged also result to a non responsive joystick of Nokia E73.The joystick motion or movement defends on the two 3D accelerometer chips. If the joystick is non-responsive you may need to rework or replace one or both of these said chips.