i can't get the variable speed to work on my p519, it's only full blast or nothing

Diagnosis

The Ryobi P519 uses a variable-speed trigger assembly that relies on a potentiometric contact system to modulate the voltage sent to the motor. When you experience "all or nothing" operation, the internal resistive track of the trigger switch has typically worn down or become contaminated with fine sawdust and metallic debris. This creates a "dead zone" where the switch fails to register a partial press, eventually jumping straight to the full-contact point that triggers maximum RPM. Another common cause is a failure in the electronic speed control (ESC) module located just behind the trigger. If a capacitor or solder joint on the control board has cracked due to the high vibration inherent in reciprocating saws, the signal from the trigger is ignored, and the tool defaults to a full-power bypass mode for safety. You can confirm this by gently squeezing the trigger; if there is a significant "gap" of travel before the motor suddenly kicks in at full speed, the physical contact strip is worn. If the tool kicks in instantly but at max speed regardless of pressure, the control board has likely shorted.

How to Fix It

Because the trigger assembly on the P519 is a sealed unit, you cannot clean the internal contacts. You must replace the entire trigger switch assembly.

1. Safety First: Remove the 18V ONE+ battery pack and ensure no blades are installed in the chuck to prevent accidental discharge.
2. Case Disassembly: Using a T15 Torx driver, remove the four primary housing screws. Note that the screws in the handle grip are deeper than the ones on the motor housing; do not over-drive them to avoid stripping the plastic threads.
3. Housing Separation: Carefully split the two halves of the plastic casing. Be mindful of the trigger spring and the locking-off button, as these can pop out and be easily lost.
4. Disconnecting the Switch: Locate the wiring harness connecting the trigger assembly to the motor. Carefully unplug the 3-pin connector. Avoid pulling on the wires themselves; grip the plastic connector head.
5. Trigger Removal: Unscrew the two small Phillips head screws securing the trigger assembly to the handle frame. Lift the old switch assembly out of the grip.
6. Installation: Drop the new replacement trigger assembly into place, ensuring the trigger lever is properly seated in the handle notch. Tighten the mounting screws firmly but do not over-torque, as the plastic frame can crack.
7. Reassembly: Reconnect the wiring harness, ensuring the click-lock engages. Align the two halves of the tool housing and replace the T15 screws in a cross-pattern to ensure an even seal.

If That Didn't Work

• Inspect the Battery Terminals: Check the copper contact tabs on the tool side of the battery interface. If they are charred or bent, they may be causing a voltage drop that confuses the speed controller, making it seem like the trigger is malfunctioning. Clean them with a cotton swab and 90% isopropyl alcohol.
• Check for Wire Chafing: Inspect the wiring loom between the trigger and the motor. Because the P519 vibrates violently, the insulation on the wires can rub through. If the "slow" signal wire is shorted to the frame, the tool will default to full speed. Wrap any exposed copper in heat-shrink tubing.
• Test with a Different Battery: A failing battery cell or a damaged BMS (Battery Management System) in an older 18V pack can cause erratic power delivery. Test the tool with a fresh High-Performance (HP) battery to rule out power fluctuations.
• Clean the External Trigger Gap: Use compressed air to blow out the gap between the trigger lever and the tool body. Occasionally, a large piece of debris gets lodged in the trigger housing, preventing the lever from reaching the "low speed" contact points.

Heads Up

• Avoid "Feathering": Avoid holding the trigger in the low-speed range for extended periods while under heavy load, as this generates excessive heat in the trigger's resistive track and accelerates wear.
• Debris Management: Use a can of compressed air every 5-10 uses to blow out the handle area. Sawdust is conductive when moist and is the primary enemy of the P519's electronics.
• Screw Torque: When reassembling, do not over-tighten the housing screws. The P519 uses a high-impact plastic that can stress-crack if the screws are driven too hard, which will eventually lead to the tool shaking apart during use.
• Blade Selection: Always ensure the blade is locked tightly in the chuck. A loose blade increases vibration, which puts more mechanical stress on the trigger assembly and internal wiring.