Thanks for the ideas - and (*looks out of the window at the weather*) I don't blame you. 
I don't think it can be the chip RAM because Agnus is the chip RAM controller, and as long as the _RESET line is low, chip RAM is out of the picture entirely.
The _RESET line is high for 0.1us only - that's not even one 7MHz cycle - so it can't be something that Agnus needs to do, I don't think. Does Agnus need to be "turned on" somehow?
But this still doesn't make sense - the _RESET line is an input, not an output! A chip should never hold an input low itself.
Edit: For those that are wondering, the +5V line is held at 5.09V.
I have repaired many green screen 3000's(mostly 3000t's) with bad chip ram, seems many of the toshiba zips used in the 3000T's went bad for some unknown reason.i am not sure this is the case with what you are seeing. If you had other colors etc. i would suspect the 3000's PALs. if memory serves the 3000 will boot with only 1Mb chip also.
Also, are you sure you didn't damage a trace to agnus when you replaced the socket? you might do a continuity check with a meter from the socket.
