my ryobi 40v chainsaw won't start at all, no light or anything, battery is charged and clicks in fine. what gives?

Diagnosis

The complete absence of LED indicator lights on the RY405110 indicates a total break in the electrical circuit between the 40V battery pack and the motor controller. Because the battery "clicks" in, the physical locking mechanism is functioning, but the electrical handshake is failing. This is most commonly caused by a failure in the terminal interface, where carbon buildup, oxidation, or microscopic debris creates an insulating layer that prevents the high-amperage current from reaching the logic board. Another common culprit for "dead" behavior on the HP Brushless series is a tripped internal safety lockout or a blown fuse in the tool's power management module. If the tool suffered a sudden stall or an overheat event during its last use, the system may have entered a protective state. You can confirm a terminal issue if you notice any slight discoloration (darkening) on the battery's gold-plated contact pads or if the spring-loaded pins inside the tool's battery bay do not "bounce back" instantly when pressed with a non-conductive probe.

How to Fix It

Follow these precise steps to restore electrical connectivity to your chainsaw:

1. Remove the battery pack and set it aside. Use a high-intensity flashlight to inspect the battery port. Look specifically for "pitting" or black carbon scoring on the four gold-plated contact pins.
2. Saturate a cotton swab with 91% or higher Isopropyl Alcohol. Firmly scrub each of the four pins inside the tool's battery bay. If you see green corrosion, use a very fine needle or a dental pick to gently scrape the oxidation off the metal before cleaning with alcohol.
3. Clean the corresponding contact plates on the top of the 40V battery pack using the same alcohol-soaked swab. Ensure no residue or oily film remains, as this can act as an insulator.
4. Perform a "Hard Reset" of the logic board: Insert the battery, then hold the trigger down for a full 10 seconds while simultaneously pressing the safety lock-off button. This can sometimes clear a latent error state in the brushless controller.
5. Check the battery's own state of health by inserting it into a different Ryobi 40V tool (like a leaf blower or string trimmer). If the other tool powers on, the issue is isolated to the chainsaw's internal wiring or port.

If That Didn't Work

• Check for Pin Recessions: Inspect the pins in the battery port to see if one has been pushed back into the housing. If a pin is recessed, it won't make contact with the battery plate. Carefully use a small pair of needle-nose pliers to gently pull the pin forward, ensuring it is spring-loaded and moves freely.
• Inspect the Safety Trigger Assembly: The RY405110 uses a dual-stage trigger. If the plastic safety lock-off lever has snapped internally, the trigger cannot engage the switch. Remove the outer casing screws and visually inspect the trigger switch to ensure the plastic actuator is actually pressing the electrical button when the trigger is pulled.
• Test with a Different Battery Voltage: If you are using a 4.0Ah battery, try a high-capacity 6.0Ah or 7.5Ah pack. Some HP Brushless motors have a higher "wake-up" voltage threshold; a battery that shows "full" on the charger may actually have a dropped cell that provides enough voltage for the charger to see, but not enough to trip the tool's power-on circuit.
• Internal Wire Continuity Check: If you are comfortable with a multimeter, open the chassis and check for continuity between the battery terminals and the main control board. A common failure point is a pinched or chafed wire near the battery housing that has shorted to the frame.

Heads Up

• Avoid using WD-40 or silicone sprays inside the battery port; these leave a non-conductive film that will cause the tool to intermittenty lose power.
• Always store your 40V batteries in a cool, dry place. Extreme humidity leads to the "green crust" oxidation on the terminals that causes this exact failure.
• When inserting the battery, ensure it is pushed in with a firm, singular motion. Repeatedly "wiggling" the battery into place can wear down the gold plating on the contacts, leading to increased electrical resistance.
• Keep the air vents near the motor clean. If the brushless controller overheats, it may trigger a thermal shutdown that prevents the tool from starting for up to 30 minutes.