Our display (using ADV7441A as video receiver) works properly for all known cases except for signals from two particular sources of analog (RGBHV) 1920 x 1200 @ 60Hz Reduced Blanking (per VESA spec) – other sources of the same format work properly. For those two sources, it appears that the ADV7441A fails to see the (apparently good) HS and VS signals, and instead reports (via the register at User Map, Address 0xB5) SyncOnGreen, and tries unsuccessfully to use the SOG (which is not present on the actual signal). We noticed that, from those two sources, the (separate) H & V sync provided is of opposite polarity from that specified by VESA. We tried setting the ADV7441 to manually use Separate HS and VS (via the register at User Map, Address 0x85), and also tried selecting sync polarities manually (via the same register), but in those cases the ADV7441 apparently sees no valid sync at all. Further experimentation finds that, if we invert the polarity of the HS signal (using external circuitry), the ADV7441 correctly/automatically identifies Separate HS and VS (via the register) and operates properly – note that inverting the VS has no effect.
Any guidance would be greatly appreciated.