JL Audio HD750/1 flashing green light

1000009785.jpg
 
They don't look defective.

Confirm that one of the 2552s (preferably a new replacement but...) reads infinite resistance to the other two terminals. If one reads infinite resistance, install it in place of the negative rectifier you have installed and clamp all FETs to their heatsinks and power up with limited current (no more than 10 amps). Does it power up?