A Repair Station Mechanic reports that a CRJ-700 returned to field when the landing gear failed to retract after take-off. Aircraft had just come out of a Heavy 'C' Check; and the Adjustment/Test of the Nose Landing Gear (NLG) 'Weight on Wheels' (WOW) Proximity Sensors had not been accomplished.

Narrative

A CRJ-700 left on a revenue flight after being returned to service after a Heavy 'C' check at ZZZ Maintenance Base. Shortly after take off; an in-flight-emergency was declared when the landing gear failed to retract. After a brief investigation it was discovered that the Nose Landing Gear (NLG) Weight-on-Wheels sensors were not adjusted properly. The installation of the NLG Upper Torque link was the most recent maintenance performed on the nose gear; and I was the Technician responsible for this maintenance.The Adjustment/Test of the NLG Weight on Wheels sensors was not performed; Quality Control did not catch it; and the problem was not discovered until the aircraft was airborne with passengers onboard. I believe Fatigue was a key factor in this incident as well as previous Quality escapes caused by mistakes made by Technicians at ZZZ; including a flap torque tube that was not installed correctly and fell off the spline shaft on a revenue flight; and an Elevator Control cable that was improperly installed and not seated on a pulley.In addition to Quality escapes; there are problems with accidents; injuries; and rework at ZZZ Repair Base. Many employees; including myself; have voiced our concerns to Management regarding the 12 1/2 hour shifts we work at ZZZ. We feel that the duration of these shifts is unnecessary; and despite being 'efficient' and 'cost effective' from the company's perspective; I believe these shifts are unsafe for employees as well as the crew and passengers that fly on these aircraft everyday.I do not feel that the company is taking our concerns seriously; and I sincerely hope a catastrophic event does not occur before the shifts are addressed. I would like to remain completely anonymous in this matter. ZZZ Repair claims that all employees are encouraged to bring safety issues to their attention without fear of reprisal. Unfortunately; I honestly feel that expressing my concerns could put my employment in jeopardy.