AD7842 Video Fifo can not lock


we am using the adv7842 as HDMI input in our devices.

With one specific video source, we have the issue that the adv7842 DCFIFO can not lock (0x68, 0x1C[4] = 0).

The TMDS_PLL is locked (0x68, 0x04[1] = 1) and also the LINE_WIDTH and FIELD_WIDTH (640x480) are shown correctly in the HDMI Tab.

When connecting the video source to a monitor, it woks fine. It also works, when connecting the sourct to a Lontium HDMI receiver.

I have also tried to connect the video source to the adv7842 Eval Board using the HDMI scripts. The results are the same, there is no DCFIFO lock.

When meassuring the TMDS clock at the input, it seems that the clock has some kind of low frequency modulation/jitter on it, compared to other video sources.

I guess this is the reason for this issue.

I would appreciate som help to solve this issue.