Sky+ HD boxes at one time could come from 4 different manufacturers , Thompson , Pace , Samsung and Amstrad. The new Sky+ HD boxes are now only built by Sky but you need to watch out when the HD box is replaced because if it is in a brown box it is a refurb and not brand new.
Sky will only supply a refurbed box which has a 3 months guarantee. You can avoid the £65 callout fee by threatening to cancel. If the box is knackered there is no attempt to repair it they simply replace it.