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Thursday, August 23, 2012

Fixing RJ45s with a paper clip

I used to carry a paper clip around with me everywhere back in my "hands on" network troubleshooting days at a school district. The admin complex had just been wired up with a bunch of new wall jacks by our contractor. New jacks had appeared everywhere. The new computers were starting to arrive that summer, and we kept getting reports of jacks which would not let the machines get on the network.

One time when this happened, someone with a punchdown tool was able to open the jack, remove the wire, and replace it with a new piece which then snapped back into the original plate. Trouble is, they were only there that one day and I didn't have one of my own.

I found myself working in that office space all alone with just a box of cable and some crimpers. I could make a new patch cord and get the user online temporarily by finding another jack in the same general area, but it was an ugly hack. I wanted to find out what was causing all of these things to fail.

Somehow, I thought to look inside one of these jacks and then the problem became perfectly clear. There should be 8 shiny copper connectors in the jack, all sitting at the same height, waiting for a cable. I saw six. The other two (one on each end) were squashed flat up against the top of the jack. They didn't reach down to meet the conductors at the end of a cable. We were running 10Base-T, so that meant 1/2 and 3/6 absolutely had to work. Losing pin 8 didn't hurt us, but losing pin 1 definitely did.

Now the punchdown fix made sense. They had just replaced the jack instead of inspecting it and possibly fixing it in place. I decided to try to pop them loose and save a whole bunch of trouble, and so a paper clip was pressed into service as a tactical jack adjuster.

Two *poink* sounds later, I had a working port and my user got online. I also showed them what I had done since it was the kind of thing anyone could notice and maybe even fix if they just knew what to look for.

I never figured out who wired up those things or exactly how all of those jacks were screwed up like that. I suspect someone was plugging ordinary six position telephone cords into them and the shell of that narrower connector was attacking pins 1 and 8. It wasn't enough that they were bent upward by this, but they also didn't retract upon removal. Somehow, they managed to catch on some kind of lip inside the jack and wouldn't come down by themselves.

It was not one of our prouder moments.