my drill sometimes just won't start, i pull the trigger and nothing happens, but if i whack it on the table it starts working

Diagnosis

This behavior is a classic symptom of a "mechanical-electrical disconnect," typically caused by a fatigued solder joint or a loose terminal connection within the DCD771C2's trigger assembly. Because the drill functions after a physical impact (whacking it on the table), you are dealing with an intermittent open circuit. The vibration from the impact momentarily forces two separated metal surfaces back into contact, completing the electrical path from the 20V battery to the motor. In the DCD771C2 model, the most common failure point is the solder joint where the heavy-gauge power wires connect to the trigger switch PCB. Due to the high vibration of drilling and the torque of the motor, these joints can develop "cold solder" cracks or hairline fractures. Alternatively, the carbon brushes in the motor may have become worn or stuck, preventing them from making consistent contact with the commutator, though the "whack to start" symptom more frequently points to the trigger housing or the battery terminal spring tension.

How to Fix It

To resolve this, you must perform a continuity check and resolder the internal connections. You will need a T15 Torx driver and a 30W-60W soldering iron.

1. Remove the 20V Max battery pack and place the drill on a stable work surface.
2. Using the T15 Torx driver, remove all housing screws. Note that some screws are recessed in deep holes; ensure you apply firm pressure to avoid stripping the heads.
3. Carefully pry the clamshell halves apart. Be cautious not to snap the plastic alignment tabs.
4. Locate the trigger switch assembly. Inspect the two primary power wires (typically red and black) where they are soldered to the switch terminals. Look for a "ring" crack in the solder—this is a clear sign of a failed joint.
5. Using your soldering iron and a small amount of lead-free solder, reflow the joints. Heat the wire and the pad simultaneously for 2-3 seconds until the solder flows smoothly and forms a concave fillet.
6. Inspect the battery terminal contacts at the base of the handle. If the spring-loaded pins appear compressed or oxidized, gently pull them outward by 1mm using needle-nose pliers to ensure a tighter grip on the battery terminals.
7. Reassemble the housing, ensuring no wires are pinched between the plastic shells, and tighten the T15 screws firmly but not over-tight.

If That Didn't Work

• Replace the Trigger Switch: If reflowing the solder doesn't work, the internal contact plates within the switch assembly may be pitted or worn. Replace the trigger assembly entirely (Part No. DCD771-S) to restore consistent current flow.
• Inspect Motor Brushes: If you see sparks inside the motor housing when it finally starts, the carbon brushes may be stuck in their holders. Gently tap the motor casing with a rubber mallet to reseat them, or replace the brush set if they are worn down to less than 3mm.
• Test Battery Terminals: Check for "arcing" marks (black carbon buildup) on the battery's gold-plated terminals. Clean these with a cotton swab dipped in 90% isopropyl alcohol to ensure there is no resistive layer blocking the current.
• Check the Forward/Reverse Slider: The sliding switch can sometimes get jammed halfway, preventing the trigger from engaging the circuit. Use a can of compressed air to blow out any drywall dust or sawdust from the slider mechanism.

Heads Up

• Avoid Over-Tightening: The plastic housing of the DCD771C2 is durable, but over-tightening the T15 screws can crack the casing, which will lead to the drill vibrating more and causing the same electrical failure to return.
• Dust Management: This drill is not fully sealed. If you use it for drywall or masonry, blow out the trigger area with compressed air every few projects to prevent conductive dust from bridging the switch contacts.
• Battery Storage: Never store your 20V Max batteries in freezing temperatures, as this can cause internal cell degradation that mimics a "dead" or intermittent connection at the terminals.
• Solder Caution: When soldering the trigger board, work quickly. Excessive heat applied to the PCB can lift the copper pads, which would permanently destroy the switch assembly.