The brake band is likely worn out or the mechanism is dirty. This is a critical safety component.
- First, inspect visually. Look for the brake band around the clutch drum. See if it's broken, frayed, or excessively thin.
- Check for debris. Sawdust and wood chips can jam the mechanism under the front hand guard. Clean it out thoroughly.
- Test the inertia function. With the engine off, give the front hand guard a sharp forward knock with your hand. It should snap into the engaged position. If it doesn't, the inertia spring may be faulty.
IF THAT DIDN'T WORK: The linkage from the hand guard to the brake band may be bent or disconnected. This requires disassembly to inspect. Do not operate the saw until the chain brake is functioning correctly.
HEADS UP: A chain brake that feels loose or doesn't engage is a major safety hazard. Do not use the saw. Have it inspected and repaired by an authorized Husqvarna service dealer.