Well i had the same thing and i found out that the mechcontrol is dead
Connect the ps2 to power suply while it's open and u can see the components.
Touch with you'r hand the Regulator switch on the down left of the bios (maked IC403), and see if it's getting very hot, check pin 4 and see if u have 1.8 volts or highr. if u do have above 1.8 and the regulator getting very hot, it means you'r mechcontrol is drawing lot's of current. touch it with the back of you'r fingers (while in standby mode) and wait and see if it heating, if it does - sorry you'r mechcontrol is dead.
PS2 V5 SCPH-30004R with messiah - sold
PS2 V5 SCPH-30004R with magic 3.1 Sold
PS2 v9 SCPH-50004 with magic V.
XBOX with X2 pro 120G HD, internal SPDIF connected to HDTV
XBOX with alladin pro