Just like any other home, the International Space Station experiences its share of breakdowns. Unlike when your faucet leaks, however, orbiting astronauts can't just pick up the phone and summon a repairman. In a way, the ISS is kind of like a $100 billion DIY project. But, you know, not really.
This time the culprit was a computer (isn't it always?) known as a multiplexor/demultiplexor (MDM). Because the station has a limited communications bandwidth, multiplexing is a vital capability. Multiplexing is a technique that allows multiple signals to be combined into a single signal that makes maximum use of the available communications space. The ISS uses several tiers of MDMs to route commands from mission controllers to various station systems.
Fortunately, the faulty computer was merely a backup system and the problem was discovered during routine testing on April 11. Less fortunately, this particular MDM was the only one located outside of the station. This means that an extra-vehicular activity (EVA) was required to replace it with a backup stored onboard the station.
You might recall, however, that recent spacewalks haven't gone too well. In fact, NASA has halted all non-essential EVAs until problems with the spacesuits have been resolved. But, even though this was only a backup component, its replacement was unavoidable. To bolster efforts, the arrival of Monday's Dragon supply ship included a new spacesuit. Despite this, astronauts Steve Swanson and Rick Mastracchio were still advised to carry water-absorbent material and small snorkels in case of an emergency.
Fortunately, no such incidents were reported and the astronauts were able to replace the malfunctioning MDM with its replacement in just over 90 minutes. That's very quick for work in space and, in fact, this was the shortest successful EVA in ISS history. Only last July's aborted spacewalk was (4 minutes!) shorter.