Is this a partial failure of the display, ... ?
This time, however, the last four columns of the LCD are in an "all dots on" mode, so that a little rectangle is shown. The LCD is set up using "lcd.begin(4, 20)", and, other than the last four columns, it works perfectly. Is this a partial failure of the display, or is some other mystery at work here?
OK, one of these is the "master" corresponding to the left-most four columns, each of the others adds four columns. In a 1602 LCD, each serves eight columns, and this relates to the odd arrangement in memory of the alternate rows of the 2004.