Ralph,
As you probably know, the power supply may show a good voltage but then fail to output properly when the load of the bulb is applied. If there is any way to get a voltmeter on the leads powering the bulb, that should show whether there is a problem with the supply.

Most projectors also have a switch that controls multiple functions including turnging off the bulb during rewind, etc. That would also be a section to check. Of course, there is the transformer that can also be involved in all this.

Sorry if this is not of much help. I would also note that it may be cheaper to buy one off eBay than to get it professionally repaired...

RalphM