My monitor only misbehaves at home

My 27-inch Thunderbolt Display keeps blanking out momentarily. Sometimes it’s occasional, sometimes it’s constant; it started a couple of months after I bought it. I’ve taken it to the Apple Store twice, and on both occasions there was no problem during the testing process. The moment I take it home it starts again. What do I do? Ram Ravishankar There was a firmware fault that intermittently blanked the display and disconnected USB devices. That was supposedly fixed back in 2012, but if you haven’t installed all available updates from Software Update, it’s possible yours hasn’t been patched yet. Also, some Mac minis have had problems with glitchy display output on the HDMI connection. Try connecting the monitor to something else; that would be a useful test to see whether it’s the monitor or the Mac display card. It’s also worth unplugging any USB devices from the monitor. If it turns out to be a hardware fault with the monitor, you’ll likely have to pay for an Apple Store (or authorised repair centre) to fix it; that won’t be cheap. Although the fault began inside the warranty period, you are now outside the EU two-year warranty limit. The onus is on you to prove it was a pre-existing fault.