I need a help i broken my ps2 power switch ribbon can i turn on ps2 without it. It is possibleYes, I'm sure it works. But imagine if you wrote that FMCB worked on all SCPH-90004 PS2s - people who have the wrong SCPH-90004 will be scratching their heads, wondering why it wouldn't work. You need to be clear that for such a case, we need the right modchip and additional software (not part of FMCB).
If you don't know, there are some SCPH-90004 models that will support FMCB, without a modchip. The 04 in SCPH-90004 is just the region (Europe), which is not related to the model of PS2.
But don't worry too much! I wrote about it, just for completeness.