I recently picked up a semi working Mac plus. I'm in the process of repairing it. I have learned that C1 on the analog board is often dead, also have a look at the AC inlet X and Y caps, the ones on mine had been totally cooked and are cracked open.
Worth a look if you are handy with the soldering iron. If you're not, I wouldn't mind taking a look at it after I have finished mine if you are still stuck.