Help appreciated - MY Book 2TB x4 all raid 01

Previously the three My Books all worked well, no issues all linked by firewire 800.

I have just added a forth drive, now I have an a problem with three out of four starting up, the main drive linked to the imac works but none of the other’s linked in series are powered on.

Occasionally all four will start up,  or drive 1 and 3 will work whilst drives 2 & 4 are not on.

I have updated to the latest firmware, bought new firewire cables!! change plugs positions - Yet problem still exists any guidance appreciated…