I'm no hardware guru, but I think the green screen can appear (as one might expect) from problems with the Agnus chip in AGA (Alice?) and/or the traces between it and the chip mem. Not much you can do about the chip if it's soldered on, but maybe the board has a flaky connection somewhere and a bit of *gentle* flexing in the area might help. If that's the case though it's likely to not be very reliable unless the fault can be repaired properly.
Maybe some small metal filing found its way into an inopportune spot on the board as well -- you never know...
