had a quick look at a sys 11 cpu and noticed that pin 20 on U51 and U54 are on the same track as the 5vdc led. (these are the closest chips on the 5 volt rail that you have tested to the 5vdc led)
if you are getting 5vdc at these points your 5vdc led should light.(but as you have said all leds are out)
have you tested that the cpu is grounded properly?
to do this check that you have 0 ohms from the the braided ground strap to TP1 (GND) (machine turned off)
then put your multimeter across TP1 and TP2 and check if you have 5vdc (machine turned on)
we will first try and get the 5vdc led going.
let me know how you go and we will go from there
