Quote:
what are the risks caused by the diode missing?
Provided the drive is powered from a known good working power supply then probably very little risk.
A better alternative would be to replace the damaged 'TVS' with a correct value component before applying power to the drive. Just borrow one from any similar drive available to you. A good tip would be to use a test meter to check for a short circuit accross the pads. If there is still a short after removal then there are more problems. If you are unsure then find a competent repair technician to the job for you though that may be much harder to find than the replacement part.