Don't know if someone's still interested in it, but few notes from me after a successful AVR 1909 HDMI board repair:
In my case it was HDMI switch IC SIL9185 (IC1002). Found out by checking 1.8V rail that goes to that chip, it was shorted. 1.8V regulator (SE111751, IC1001 on board) was fine, provided 1.8V after removing 9185 IC. Ordered SIL9185A since it was cheaper here at local store, i believe they are just different revisions and should be compatible with each other.
BTW, before replacing chip, i tried to "bypass" it by removing chip and soldering input-output pins together. I had video from HDMI, but no audio. Looked at the schematics and i believe sub-cpu doesn't turn on DSP processor when it doesn't detect signal from SIL9185 chip, so IC has to be replaced anyway
More thoughts about whole HDMI board schematics and what could cause these common problems:
Onkyo receivers (like TX SR606 & SR607) have very similar hdmi board architecture (SIL9185 and SIL9135 chips on input side), but around 1.8V regulators and 3.3V input rails they have electrolytic capacitors which tend to dry out and fail over time. There are many repair guides around (just google it, i can't post links since i don't have 5 posts) . Denon has ceramic smd capacitors there, so voltage regulators themselves or ICs they supply could fail there more often, not caps themselves.
Digging deeper to what could cause HDMI input side problems i guess it's +5V from crappy, non-grounded input devices. Newer devices have DSP problems more often due to overheating, but that's another story i guess.
Hope this helps someone