1)Make sure that the blades are inserted all the way into the handpiece. The curve of the blades should touch the curve on the guide of the handpiece. Tightening the set screws on an improperly inserted blade will cause damage to the blade. Link to our YouTube video: How to Properly Install Blades on the FT-8004 Handpiece - YouTube
Pictured below is a fully inserted blade(left) and an improperly inserted blade(right).
Dents in the blade caused by tightening the set screws when the blade is improperly inserted.
2) If this does not solve the problem, check the resistance of the blades at room temperature using a multimeter. The measured values should be 3.5Ω ± 10%. If the measured values are not within this range, the blades need to be replaced.
3) If the other methods don't solve the problem, check the handpiece for continuity. Measure the resistance between pins 1 and 5 using a multimeter. The measured value should be within 6.2Ω - 8Ω. If the value is not within this range, the handpiece needs to be replaced.