my dewalt dcd771 drill won't start at all, battery is charged, what's wrong?

Diagnosis

The most frequent cause for a total loss of power in the DeWalt DCD771C2 is a mechanical lockout. The forward/reverse slider is designed as a safety trigger lock; when positioned exactly in the center, it physically prevents the trigger switch from depressing. If the slider has shifted slightly or is stuck halfway, the tool will appear dead even with a fully charged 20V battery. Beyond the lockout, a "no-start" condition often stems from a failure in the battery terminal interface. Carbon buildup or debris inside the battery rails can prevent the positive and negative terminals from making a secure electrical connection. In more severe cases, the internal trigger switch assembly may have failed due to dust ingress or a burnt contact, or the battery's internal protection circuit (BMS) has tripped due to an over-discharge event, rendering the pack dormant despite showing a "charged" light on the charger.

How to Fix It

Follow these steps in sequence to restore power to your drill:

1. Reset the Directional Lock: Locate the sliding switch above the trigger. Firmly push it all the way to the left (Forward) or all the way to the right (Reverse). If it feels "mushy," toggle it back and forth several times to clear any plastic debris that may be preventing the switch from fully engaging the trigger mechanism.
2. Perform a Hard Battery Reset: Press the battery release button and slide the battery pack out of the tool. Inspect the metal contact plates on both the battery and the drill housing for black carbon scoring or dust. Use a dry cotton swab or a can of compressed air to clean the terminals.
3. Secure the Connection: Slide the battery back into the mount with a firm, decisive motion. You must hear a distinct "click" from the locking tabs. If the battery is slightly loose, the vibration of the trigger press can cause a momentary break in the circuit, preventing the motor from spinning.
4. Test the Trigger Stroke: Gently pull the trigger. The DCD771 features a variable speed trigger; if the internal spring is worn, you may need to pull the trigger more firmly than usual to bridge the electrical gap.

If That Didn't Work

• Cross-Test with a Known Working Pack: The DCD771C2 comes with two batteries. Swap to the second battery. If the second pack works, the first battery has a failed cell or a tripped internal fuse. If neither pack works, the issue is internal to the drill's trigger switch or the motor brushes.
• Check for Debris in the Chuck: If the motor hums but the drill doesn't spin, the chuck may be jammed. Try to rotate the chuck by hand (with the battery removed). If it is seized, the motor's internal overload protection may be preventing the tool from starting to avoid burning out the windings.
• Inspect the Trigger Switch Assembly: If you are comfortable opening the casing, remove the housing screws and inspect the trigger switch wiring. Look for any pinched wires or disconnected solder joints. The DCD771 uses a simple momentary switch that can occasionally fail if the tool has been dropped on its side.
• Verify Battery Voltage with a Multimeter: Set your multimeter to DC voltage and probe the battery terminals. A "charged" light on the charger can be misleading if one cell has dropped below 2.0V. If the battery reads significantly below 18V, the pack is defective and needs replacement.

Heads Up

• Avoid "Half-Pressing": Never store your drill with the trigger partially depressed or the forward/reverse switch in the center position if you are transporting it in a crowded toolbox, as this can wear down the safety lock.
• Terminal Maintenance: Every 3-6 months, wipe the battery contacts with a small amount of isopropyl alcohol to prevent oxidation, which is a leading cause of intermittent power loss.
• Thermal Protection: If the drill stops during heavy use, it may be in thermal lockout. Let the tool cool for 15 minutes before attempting to restart; forcing it can permanently damage the motor windings.
• Battery Storage: Do not store your 20V Max batteries in freezing temperatures, as this can cause the cells to degrade, leading to the "dead battery" symptom even after a full charge cycle.