Sorry to hear about the dead BCF.
Here is a tear down pdf. but I guess you might already be there.
Here is a tech page that may be useful.
I don't know of an available cct diag. but standard procedure is to re-plug connectors and any socketed chips.
You have checked the power rails, check that it is the same on all boards.
Look for any leaky caps and any electros that have their tops popped.
The failure mode you describe is most likely a loose lead or EPROM chip and I hope it is as simple as that.
All the best
Royce