On 05/15/2012 01:06 PM, Barry Callahan wrote: It's a very common mistake; I've even made it myself, after having used them (but not having had to repair one) for decades. Two big "giveaways" indicating a linear supply are the presence of a big power transformer and a 723 voltage regulator. However, the 723 also works well as a switching regulator controller, which DEC did, and front-ended it with a big power transformer. It wasn't until actually having to dig into these regulators, while repairing a PDP-11/50 in which all but one of them had died (mostly bad zener diodes), that I learned that they're switchers. -Dave -- Dave McGuire, AK4HZ New Kensington, PA