I am having the exact same issue where columns 0 – 16 are dim and 17 – 25 are bright. When I swapped the U4/U5 chips then now the right side is brigh and the left side is dim. Any suggestions?
Just prior to all this I had tested all the LED’s lit up correctly before I started soddering. I then soldered a four in the uppoer corner and everything was ok. I then started to sodder the first column down and as I was testing I noticed that none of the LEDs would light up at more and have no idea what happened.
I may end up starting over and using the socket example I saw which seems easier to assembly than dealing with all these LED leads.