Somewhat random QBus backplane / chassis question

Hi all -- I've got an 11/03 backplane here (designated as an "11/03 EA" originally but marked as "Model changed from EA to AA") inside a small chassis w/power supply, model "OH780-A."? (So it was at some point in its life the front-end to a VAX-11/780.)? As far as I can tell, it has a standard H9270 backplane (4-slot, quad width) in it. The chassis appears to work fine when I have an actual LSI-11 in there (I've been experimenting with an 11/23, but I do have an 11/03 boardset that works in it). What I want to do with the chassis is use it with a UNIBUS->QBus bridge I have, as a Qbus backplane for a SCSI controller (and maybe other things) for my VAX-11/750.? I have encountered an oddity in doing so, and I've looked at the documentation and I remain puzzled.? The oddity is this:? If I don't have an LSI-11 CPU board in place in the chassis, the power supply won't come up properly.? (The +5V appears to pulse, the kind of behavior I'd expect with a shorted or heavily loaded supply rail somewhere). Here's a basic rundown of what I've observed: - If I put an 11/23 or 11/03 CPU in, everything works fine. - Doesn't matter what slot the CPU's in either, as long as there's a CPU board somewhere in the thing, all's well. - Doesn't matter how heavily or lightly loaded the backplane is; I've tried it with just a QBus SCSI controller, I've tried it with the backplane stuffed full of boards. Since I want to use this as a simple QBus backplane, I don't want to have a CPU board in place.? I haven't seen this behavior before (but then, I can't recall trying to run a Qbus backplane without a CPU in it either).? I thought I knew QBus fairly well, so I assume I'm overlooking something obvious.? Or perhaps there is a fault here with the chassis, somehow.? I figure someone here will have the answer immediately and I'll slap my forehead... Thanks as always, Josh