my dewalt oscillating tool won't turn on at all, battery is charged and works in other tools.

Diagnosis

The complete failure of a DeWalt DCS354B to power on, despite a known-good battery, typically points to a failure in the electrical continuity path between the battery terminals and the motor. The most common culprit is the trigger switch assembly. Because this tool is designed for sanding and cutting, fine particulate dust (drywall, wood, or masonry) frequently bypasses the housing seals and settles inside the switch mechanism, creating an insulating layer that prevents the electrical contacts from meeting. Alternatively, the issue may be "terminal creep" or a fractured solder joint. The DCS354B experiences significant vibration during operation, which can cause the wiring harness connecting the battery rails to the trigger switch to fatigue and snap, or cause the internal switch spring to lose tension. You can confirm this by checking for any "click" feel in the trigger; if the trigger feels mushy or has no tactile resistance, the internal spring or plastic actuator has likely failed. If the trigger feels normal but there is no movement and no LED indicator light (if applicable), the break is likely at the terminal connection or the switch itself.

How to Fix It

To resolve a power failure on the DCS354B, follow these steps to clean and inspect the internal electrical path:

1. Remove the battery pack and use a can of high-pressure compressed air to blow out the battery terminal slot. Focus specifically on the copper rails to remove any metallic shavings or sawdust.
2. Inspect the battery terminals inside the tool for "arcing" marks (black carbon buildup). If present, use a small piece of fine-grit sandpaper or a cotton swab dipped in 90% isopropyl alcohol to scrub the contacts until they are bright copper.
3. Remove the rubber grip overlays and the housing screws (typically T15 Torx) to access the internal chassis.
4. Locate the trigger switch assembly. Apply a small amount of electronic-grade contact cleaner (such as DeoxIT) directly into the gaps of the switch mechanism.
5. Rapidly cycle the trigger 20-30 times to work the cleaner into the contacts and break up any internal oxidation.
6. Inspect the two primary wires leading from the battery rail to the switch. Gently tug on these wires; if one pulls free from the solder joint, you have found the break. Re-solder the connection using a 60/40 rosin core solder.
7. Reassemble the housing, ensuring no wires are pinched between the plastic shells during closure.

If That Didn't Work

• Replace the Trigger Switch Assembly: If cleaning fails, the internal diaphragm of the switch is likely burnt out. Order a replacement trigger assembly specific to the DCS354B. When installing, ensure the plastic actuator arm is seated perfectly in the trigger groove to avoid "ghost" powering or jamming.
• Check the Motor Brushes: While this is a brushless tool, internal debris can still jam the rotor. Use a vacuum to clear the motor vents. If the tool hums but doesn't spin, the problem is mechanical (seized bearing) rather than electrical.
• Test with a different Battery Voltage: If you are using a 20V battery, try a 60V FlexVolt battery if available. Sometimes a high-amperage battery can "punch through" a high-resistance dirty contact that a standard 20V pack cannot.
• Inspect the Battery Rail Springs: Check if the spring-loaded pins in the tool's battery port have lost their tension. If they don't spring back quickly, they won't make a solid connection with the battery terminals. Gently bend them back into place using needle-nose pliers.

Heads Up

• Avoid using WD-40 inside the switch; it leaves a sticky residue that actually attracts more dust, which will lead to another failure in a shorter timeframe. Use only non-residue electronic contact cleaners.
• Regularly blow out the motor vents with compressed air every 10-15 hours of use to prevent dust buildup from reaching the internal circuitry.
• Always ensure the battery is fully seated with a distinct "click" before pulling the trigger; repeated partial connections can cause arcing that damages the battery rails.
• If you replace the switch, check the rubber boot seal. If the seal is torn, replace it, or the new switch will fail again within weeks due to dust ingress.