Apple’s (AAPL) new 27-inch iMacs are truly terrific all-in-one desktops, but the company has so far had trouble manufacturing enough of them to start shipping. But now BrightWire is citing a report in the China Times claiming that Apple and its supply chain partners late last year finally figured out how to get more consistent manufacturing yields on the 27-inch iMac and started mass producing the computer in December. What this means, says BrightWire, is that new iMac shipments will get a boost to start the new year and “are expected to remain stable through Q1 2013.”