Mac Hard­ware

Think­ing in­side the alu­minium box to re­fresh the parts that other tips can’t reach

Mac Format - - GENIUS TIPS - by Bob Pringle

Black screen iMac lock­out

QAt seem­ingly ran­dom times, the dis­play of my iMac (21.5-inch, Mid 2011) goes com­pletely black, and the sys­tem is then un­us­able, so I have to per­form a forced shut­down us­ing its power but­ton. This iMac has a Radeon HD 6770M graph­ics card. Why is this hap­pen­ing?

AGiven its vin­tage, a dy­ing graph­ics card or other hard­ware could be to blame. Sev­eral mod­els of graph­ics cards have suf­fered pre­ma­ture fail­ure, prob­a­bly be­cause of the in­tro­duc­tion of lead-free sol­der, and some have had their war­ranties ex­tended as a re­sult.

Be­fore you take the Mac in for re­pair, check its logs in Con­sole. Af­ter this next hap­pens and the Mac has restarted, open Con­sole and search for BOOT_TIME, which should take you back to the last startup. The en­tries right be­fore that may give a bet­ter idea as to what went wrong at the time of the black screen.

Oth­er­wise, run Ap­ple Hard­ware Test or Di­ag­nos­tics (see the next page); if that re­ports a hard­ware fault, you’ll need to take the Mac for re­pair. If the hard­ware checks out OK, the Mac could still have a graph­ics card prob­lem, which may only be pos­si­ble to fully di­ag­nose by Ap­ple’s in-house tools.

The Mac may be in­ad­ver­tently try­ing to en­ter Tar­get Dis­play Mode (as when you press

ç+@). You might stop that by tem­po­rar­ily restart­ing in safe mode, or by check­ing the set­tings in the Dis­plays pref­er­ences pane.

Re­view­ing set­tings in Sys­tem Pref­er­ences can halt dis­play prob­lems, but they’re of­ten due to a fail­ing graph­ics card.

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