Contents:

Repair broken ASUS router switching power supply (seemingly a router failure)

The power supply failed

Symptoms

What is happening here?

Fix

Opening the power supply

Replace the capacitor

Repair broken ASUS router switching power supply (seemingly a router failure)

The power supply failed

LED stateMore models of ASUS routers (WL-500g Premium, WL-500W and probably also others; please report) use the same switching power supply 5V/2.5A. This power supply often fails in a way that people thinks that the router is dead and the whole router goes to trash.

The reason is the failure of a single electrolytic capacitor and one can repair it for no more than 25 cents.

I already seen two power supplies with the same failure.

Symptoms

power supply at load shows about 3Vpower supply at load shows about 5VIf your power supply failed in the described way, you can easily detect by the behavior:

  1. Router boots into a strange state and does not respond:
  2. Voltage without load is near the correct 5V.
  3. Voltage with load drops down to about 3V. If your router has an USB port, you can easily check the voltage under load with a voltmeter on the USB connector. If not, you either have to open the router or attach a load simulating 2A load (e. g. resistor around 10Ω) to the power supply.
  4. When you open the power supply, you will see a bulged electrolytic capacitor.

What is happening here?

The failed electrolytic capacitor is the main power capacitor on the secondary side. If the capacitor fails, its capacity decreases and the internal resistance increases. As a result, the power supply cannot provide 5V 2A at load. The router needs such a high current only in some stage of booting. The router starts to boot, then voltage decreases and router stays stuck. That is why some LEDs are on. In fact, the LED status represents the last status before the voltage drop and operational failure.

The fix

Opening the power supply

bulged capacitorteardown of the power supplyThis is the most complicated step. The power supply is glued and you need a sharp blade (e. g. snap-off blade utility knife) to open it. Use a slant cut, deeper side is farther from the power plug. Do not go too deep, as you risk cutting of the electronic parts.

Replace the capacitor

You will see a bulged capacitor. Use vacuum desolder to remove the old one and replace it by the new one. Respect the polarity! The capacity is not critical, higher is better. Much more critical is the internal resistance, lower makes the capacitor life much longer. Surely you have to use Low ESR capacitor. The original capacitor was Low ESR 1200µF/10V. Even Low ESR 1200µF/6.3V will work, if you pick a high quality one. But the space inside allows to use up to Low ESR 2200µF/10V.

You are done! Now attach a bit of glue, close the power supply, and your router should boot again.

Update after 2 years: Capacitor Jamicon 1500µF/6.3V/105°C (Low ESR) lasted there 2 years of 24/7 work, i. e. 3 times less than the original.