Only purple lines on startup

Machine came to me and on startup had one wide purple line in the middle and no startup chime. I pulled the drive and replaced the power supply. Machine booted great off of a flash drive with Catalina installed. Ran the machine for 2 days. Ran apps, cruised the web, restarted, shutdown and started up, basically put the machine through its paces with no trouble. Picked up an SSD and installed. Now when it starts I get the chime and the wide purple line and then a bunch of thin purple lines in the middle and edges of the screen. I have unplugged and replugged the 2 display cables a number of times. I have checked the cables and sockets under magnification for damage and see none. I have wiggled the cables while the machine is running with no change. I disconnected the SSD even, no change. I tried resetting the PRAM, no change. Has anyone seen this and resolved it? Any insights are appreciated.