Fixing a Linksys SD2008 running at 100 Mbps

We were having some networking issues at work where our Macs had problems with our Widows 2003 R2 file server. They could connect just fine but browsing was just painfully slow and file transfers were hit or miss. Our Vista and XP machines were running just fine. Googling turned up a command line you could try but that didn’t work for us. I found that manually setting the gigabit-based machines to 100TX seemed to fix the problems sometimes but not always. Eventually I traced the problem to a switch that when the Macs and the file server were connected to it would cause the problems. The quick fix was to put all Macs and the file server on the other switch but unfortunately that switch is only 100-based.

So then I brought in a friend to help and after a little standard troubleshooting we found that if we connected the server to the gigabit switch it reported that it was only connected at 100Mbps but if we plugged his laptop into the switch he got full gigabit. First thought – the wire. Unfortunately using the same wire that he tested with still resulted in 100Mbps for the server. Second thought – the port, but all ports acted the same. Third thought – the NIC. But, after swapping the NIC out for a known-good NIC we still only got 100Mbps.

Both NICs that we were using were Intel Pro/1000 GT Desktop adapters with Windows-supplied drivers so we tried upgrading to the latest drivers from Intel. Thankfully they came with a diagnostic utility that after we ran it reported “The cable connected to this port is missing pairs needed to connect at 1000 Mbps”. So now we were pretty confident that the problem was with the switch but in my experience switches either are working, have dead ports or are just plain dead. I’d never run across a switch “partially working”. After a little more Googling I found an article that talked about “bulging capacitors” on Linksys SD2008 models caused by overheating. So I finally cracked the Linksys SD2008 open and found that indeed I had four bulging capacitors.

Bulging Capacitor

In the image on the right, the center capacitor is “bulging”. (This image is not from my Linksys but shows a good close-up.)

The capacitors for my Linksys SD2008 were 470uf 25V so I ran out to RadioShack and picked up four 470uf 35V capacitors. (When purchasing capacitors its very important to match the capacitance which is measured in Farads (F) or microfarads (?F) exactly but the voltage doesn’t matter as long as it is equal or greater.) Using a soldering iron I pulled off all four and re-soldered on the new ones and then plugged everything back in. My new link tests now showed full gigabit! I then tested the Macs and they showed full gigabit as well as having zero problems with file transfer and browsing! Sweet!