Monday, October 01, 2012

Asus WL-500W router bad capacitors

My WL-500W wireless router recently became unstable. It was still perfectly fine for web browsing, but any large data transfers over wireless caused reboots. At first, I only noticed this with copies over the LAN, but a few days ago even a fast download from the Internet caused a reboot. At first I thought this was a bug with the firmware I use, but going back to a version that used to be perfectly stable did not help.

I found some info online about bad capacitors in Asus routers, so I decided to investigate. I chose to first look at the router, because it is easier to open. That just involves removing the glued on rubber feet, unscrewing the Phillips screws that were hidden by the feet, and lifting off the top. I immediately noticed a bulging capacitor near the toroidal inductor near the power input. It's used for filtering 3.3V power, so it's quite important.
This made me also wonder about the power supply wall wart. People were reporting bad capacitors there also. Since looking inside requires violent disassembly, I first measured the voltage to see if there might be a problem. Open circuit voltage was okay, but when the router was connected, the voltage drooped below 4V, which is obviously bad.

I opened up the wall wart by hammering a blade into the seam at various locations. This was much quicker and easier than sawing it apart. Then I had to yank out the circuit board, which was glued with silicone. The 1200µF 10V output filtering capacitor was bulging and leaking. After replacing it, the, voltage droop under load became much more reasonable.
After replacing both of these capacitors, the router was stable. As long as it's stable and the other capacitors don't look obviously bad, I don't feel like replacing them. This does however make me hesitant to glue the wall wart back together. For now I'm using a rubber band, and I guess I'll replace that with cable ties.

This wasn't too hard, but I shouldn't have to deal with bad capacitors in a product manufactured in 2008. I'm disappointed with Asus. By 2008 they should have learned how to avoid this problem. I guess the capacitor plague continues. Wikipedia even has an "after 2007" section in the article.

Finally, here are photos of markings on the two bad capacitors. The obscured number at the top is 8011D.

No comments: