I am observing odd behaviour when passing video through my ADV7401 device. I suspect it has to do with grounding but I would like to ping some ideas from this community since it has helped me a great deal in the past.
I have a ADV7401 device in my design configured to accept video on AIN 1, 2, 3 and it pass it through over the 24bit output to an FPGA.
When I place an osc probe on the data line at pin 41 (P3, second LSB) I can see evidence of video but over time (~5min) the video diminishes, not in amplitude, but in value. The vertical lines on my scope between the syncs are such that I am initially seeing many transitions but as the ~5min mark approaches, the value lessens such that I'm seeing less frequent transitions until finally, there are none, and I see a flat line at 0V. I ran this test multiple times and observed consistent behaviour.
I ran a third test, this time putting my probe on a MSB (P9) and saw that the video disappeared quickly (just over ~2min). I then probed an LSB (P3 again) and saw video for the remaining ~3min.
Can anyone suggest why I am seeing such odd behaviour? It would seem like my grounding reference is rising.
Other test points I can probe to help narrow in on the root cause?
I am only using AIN 1, 2, 3 and SOG. All other video inputs (AIN 4- AIN 12, SOY) are not connected (floating). Could this be an issue?
The video input is VGA at a resolution of 720x576 50Hz interlaced. Should the FB pin be pulled high? Low? We are not using SCART.
I can provide more details as needed.
Thanks in advance for your help.