Measure the voltage on the purple and green wires. You should see roughly 12V (standby) on the purple wire and a low logic voltage (approx. 4.4V) on the green wire.
Because this PSU contains high-voltage capacitors that can hold a charge after being unplugged, follow these safety steps:
Once the motherboard sends the "PS_ON" signal (by shorting the green wire to ground), the main PWM (Pulse Width Modulation) controller starts the high-power DC-to-DC conversion. Critical Components and Common Failure Points ps42419ha schematic work
Incoming AC passes through a fuse and an EMI filter to remove noise. A bridge rectifier then converts it to high-voltage DC (around 145V–160V depending on load and region).
Understanding how the schematic works is essential for repairing this 240W Hewlett Packard (HP) power supply unit (PSU). Primarily used in HP desktop towers, this "80 PLUS" efficient model is known for specific failure points in its standby and primary rails. Overview of the PS-4241-9HA Architecture Measure the voltage on the purple and green wires
A small resistor often acts as a fuse for the standby IC. If the IC shorts, this resistor usually burns out as well.
This integrated circuit (IC) manages the standby voltage. If the PSU provides no standby voltage (0V on the green/purple wires), this IC is often blown. Replacing it with a slightly more robust 20W version is a common fix. Because this PSU contains high-voltage capacitors that can
Always use a discharge tool (like a high-wattage resistor) on the primary capacitor before touching the board.
This circuit operates even when the computer is off. It provides the "wake-up" signal power.