Need help with dead 11/23+

Now that my VT220 is working again after I replaced the defective LK201 keyboard, the 11/23+ (4 Mb, two RL02's) it's attached to has died!! Last week, although the keyboard was dead, it would come up as far as the prompt: 2048. KW START? to which I couldn't enter the usual "Y", of course. Now nothing comes up at all and the RUN lamp lights for about 3 seconds, then goes out. About 6-8 seconds later it flashes briefly. Entering various things from the keyboard e.g. Y<CR>, 773000G<CR> etc. has no apparent effect. Installing the "Field Service Test Jumper" (console port loopback) causes characters to echo to the screen, so the VT220 and port are ok. I pulled all the boards except the CPU - no change. +5 and +12 supplies (measured on the board) are spot-on according to my Fluke DVM. LED's lit on the KDF-11BA board are: green (Power), and D4 and D5 (the two LSB red ones). If the HALT front panel switch is down, then all four red LED's stay on after flipping the restart switch. Can someone point me to a table of the diagnostic LED meanings? The KDF-11BA User Manual mentions them but I can't find a list of just what they indicate. thanks for any helpful hints -Charles