I had a dead (still dead) A4000 board with similar symptoms (black screen to dark grey then nothing). I had all the caps and most of the custom chips swapped/replaced. Turns out after all that I examined the pin contacts of the Bridgette chip and found one of the chip legs had broken free of the pin trace so you might check there. My attempt to reattach the pin leg resulted in a broken pin so I desoldered the chip completely and have been looking for some time for a replacement Bridgette.
