Have you tried using some load on the 12V rail? Some powersupplies do not power up if there's no electrical load.
I'm also working on replacing the innards of an A3000T powersupply, but I've used the ATX poweradapter that has been created by Matze from the A1k.org forum. This adapter has some large resistors for drawing some power from the powersupply. It works flawless.
