I hooked up an oscilloscoop on the 4 lines and compared the lines from the UNO vs MEGA2560
Put on the two Arduino's the same sketch
The data pin 11 on the UNO and the pin 51 on the MEGA have the same signal
The clock pin 13 on the UNO and the pin 52 on the MEGA have the same signal
and here comes the problem i think with the MEGA
on the latch pin 2 on the UNO i have a signal but not on pin 2 on the MEGA
also blank pin 4 on the UNO i have a signal but not on pin 4 on the MEGA
So there is no latch and blank signal from the MEGA
I hope you can help me with this CrossRoads
or someone else