In your schematic of TX1 devkit you have a series 100nF capacitor (DC block) followed by a 3.3R resistor that sits in parallel across a common mode transformer (DLP11SA900HL2).
I followed this example on my custom carrier board and it works quite nicely.
I’m wondering why the resistor is in parallel to the common mode transformer
- doesn’t that defeat the purpose of the common mode choke?
Also you have HDMI termination consistent of 600R beads + 499R resistor to ground from each line connected to a transistor with a signal called EN_HDMI_TERM
- I don’t see this pin (B23) being toggled anywhere in the sources?
- What is the purpose of this termination - i.e. when is it supposed to be turned on and off?
In a new version of my carrier board I decided to use a more integrated protection device and switched to having this structure:
100nF series capacitor ---+---> ECMF06-6HSM16 -> HDMI plug | +--- 600R bead --> 499R --> transistor to ground
This however doesn’t seem to work as good as the previous approach - some monitors work just fine but the majority of the ones I have tried fails to show an image (they remain as if they are unplugged)
Sadly I don’t have a HDMI signal integrity checker so I’m unable to check the eye diagram which I suspect may be distorted (I assume this must be the case since it doesn’t work)
Do you have some suggestions on how I can easily try and mess with the HDMI registers to see if I can make it work by increasing drive strength etc… (using trial and error approach) also where do you suggest that I start?