VAX 11/730 quickie

Just started working on mine - been a back-burnered project for a long time. Unfortunately all the cables were cut when it was dismantled; I was lucky to grab just the CPU. Got it powered up ok - no drama there. I faked cables to the port on the WCS which drives the console and hooked up my trust VT220 at 2400 baud. Nada. No self-test prompt; no ROM> prompt. Maybe I've messed up the faked console cable; I'll check - already tried obvious things like making sure Rx & Tx were crossed (it's a three wire cable according to the schematics - Rx Tx Gnd; no flow control). But I'd like to know more about the assorted LEDs on the CPU boards; maybe there's a clue there if it's not getting far enough into the self-test to display console output. There's a fair few LEDs on the M8391. But the doc I've looked through on Bitsavers doesn't seem to document their meanings and interpretations. Can anyone help on that point? Hopefully this link works: https://www.facebook.com/photo.php?fbid=10208521465663997&l=867897c786