Q: Gray vertical band on display iMac 27 inch

Hi,

I have an iMac late 2012 model 1419.  I recently upgraded the internal hard drive with an SSD m.2.

I followed the instructions for upgrade very carefully and knew it was a risk opening up the case.

I know that this was not recommended but I have upgraded many mac's before without issue. 

On this occasion I had some issues I now have a gray vertical band on my display after reassembly.

I'm wondering if this is purely a cable problem that I might have damaged the display cable or if the display it'self is bad.

I tried reseating the cable no change, using an external display works fine

Other that the band up and down the display works fine.

Does anyone know enough about this to help diagnose the problem properly before I spend on a new display screen.

The cable is only $28 to replace but the screen looks expensive