At launch an electrical fault between two of the magnets reportedly caused an arc of electricity, which in turn triggered a helium leak and explosion.  As a result, the proton tube was contaminated with soot, and the magnets were broken off from their mountings.  Months of repairs revealed more leaks in the vacuum of the insulating layer surrounding the proton tube.

Now the European Center for Nuclear Research, or CERN has declared that the repairs are done.  States CERN in a press release, "[Tests] will initially run at an energy of 3.5 TeV per beam when it starts up in November this year.  This news comes after all tests on the machine's high-current electrical connections were completed last week [the week of July 27], indicating that no further repairs are necessary for safe running."

Still, the restart represents caution on CERN's part -- 3.5 TeV is only half of the beam's full intended operational power.  States CERN Director General Rolf Heuer, "We've selected 3.5 TeV to start because it allows the LHC operators to gain experience [with] running the machine safely while opening up a new discovery region for the experiments."

There remain concerns about whether the device is capable of running at full power.  Describes CERN:

Following the incident of [Sept. 19, 2008] that brought the LHC to a standstill [due to a faulty magnet connection], testing has focused on the 10,000 high-current superconducting electrical connections like the one that led to the fault. These consist of two parts: the superconductor itself, and a copper stabilizer that carries the current in case the superconductor warms up and stops superconducting, a so-called quench. In their normal superconducting state, there is negligible electrical resistance across these connections, but in a small number of cases abnormally high resistances have been found in the superconductor. These have been repaired. However, there remain a number of cases where the resistance in the copper stabilizer connections is higher than it should be for running at full energy.

However, CERN also says that it has tested and repaired a large number of these faulty copper connections.  It says that the final two sectors it tested revealed no abnormalities.  Nonetheless, after all the headaches, it plans to throttle up the 17-mile long accelerator loop slowly, just in case there's still undetected problems.