Black screen after replacing fusion with SSD

The first time I had black screen i realised a small piece of the LDVS cable connector was damaged. I ordered a new cable but get the same black screen. If i connect a bootable drive to USB i can hear it booting up.

I do not get any image on an external monitor through the thunderbolt. the external Screen works fine through thunderbolt on my mac mini.

Therefore I am very confused , surely if the replacement cable was at fault i’d get an image on the external? The connector on the motherboard looks fine

Not backlight issue ,shined a bright light on the screen after a few minutes

I have done this many times in the past without hiccups ( i have a home business of repairing macs and upgrading )

So can someone confirm either way that a faulty cable will cause no image on an external?

will some kind of smc reset work perhaps?