The big news from HBO at Time Warner’s investor meeting Wednesday overshadowed another surprise announcement that Turner Broadcasting would take a $400 million write-down on programming expenditures.

Turner execs didn’t elaborate on the specific shows that would be written off, nor would execs comment on the matter. But the $400 million figure was seen as a stunner by seasoned industry observers — and more evidence that the management of Turner’s cablers is in need of an overhaul.

Sources say a significant portion of the write-down is coming from two megabuck off-network acquisitions that have been disappointing performers for TNT: “Hawaii 5-0,” from CBS’ syndie arm, and “The Mentalist,” from Warner Bros.

Turner paid a whopping $2.5 million an episode back in 2009 to snag “Mentalist” (pictured) rights; the show is about to head into its seventh and final season. “Hawaii 5-0,” now in its fifth season on CBS, is believed to have grabbed about $2 million an episode in a 2011 deal with TNT.

The write-down news came during a tough week overall at Turner, as the company began implementing layoffs and buyouts of nearly 1,500 staffers across its various divisions. And the company is also finding it an uphill climb to fill its top programming job after months of courting various TV biz insiders.

As recently as earlier this month, former Fox and NBC executive Kevin Reilly was seen as a lock to fill the leadership void at TNT and TBS left by the departures this year of entertainment chief Steve Koonin and programming prez Michael Wright. Now, sources confirm that Turner and Reilly have mutually decided to part ways.

The end of Reilly’s talks with Turner, first reported by Deadline, have stirred renewed speculation about Turner trying to woo Sony Pictures TV exec Zack Van Amburg. Just a few months ago, he signed a new deal to remain co-head of Sony TV’s domestic production unit with Jamie Erlicht.

A rep for Turner declined comment on the write-down and the executive search.