Wow ok so it seems you have all the tools and experience, what area of electronics do you work in?
I think if Planar themselves did not share the schem's they will be near impossible to find...
Did you test the ballast and the bulb? The ballast returns gain amount to the PSU so if anything is off with the bulb or ballast, it will send a signal to interrupt/lower the power.
That +3.3V that you are reading at +1.65V is it going from the PSU to the ballast?
How did you test the lamp? The bulb (being mercury vapor uhp) has an arch, so even though you think it being A/C you can test, but there is an arch gap in the ignition chamber that will make normal testing impossible.
The output of the ballast to the bulb is generally between 5kV and 15kV so keep that in mind if testing it!! don't wanna damage or un-calibrate your gear.
Without getting too technical, I would visually inspect the lamp, if this was working at one time I think the main board (if there was no short) should be ok. DLP projection, if you read or have read already online, is pretty steady. The most common components being the lamp, ballast and colorwheel, that when bad send signal to the main and/or psu to cancel the boot. Then we have the internal components that do go out fairly less common like you know the power supply, the main, the input board and such.
I have spent tons of time trying to find voltage errors on boards only to find the lamp was bad, this is why I keep mentioning it!
Finally do you have a part number of the psu board? maybe i can find a compatible model that uses it (since like you must know, brands sometimes mix and match) that is more popular and find the diagram for that one..?
Good luck, Happy St Patrick's Day!