Problem and Fix
Loss of audio
In my case, the unit could not call up the firmware version of the DSP1/ETH, DSP2, or DSP3. Instead it would just show ????'s for 3 of the firmware versions. (To pull up this information, with the unit on push and hold the 'display' button, then push the 'standby' button. Immediately push the '<' or' >' button by 'display').
It also would not connect to ethernet or get an ip address, and would not read or initialize from a USB drive.
Diagnosing the problem
Those who have sent the unit away for repairs on AVSforum have reported that the service shops replace the 'HDMI Board'. The board seems to be the digital mainboard, as it houses a _lot_ of DSP, DTS, and Silicon Graphics chips. The cost reported is in excess of 600 dollars, which was out of the question for me to pay to repair a free unit.
Two of the chips on the board were in BGA (http://en.wikipedia.org/wiki/Ball_grid_array) form factor- which with poor cooling has been noted to cause problems in northbridge and video chipsets in laptops as well as the famous red halo of death in xbox 360s.
I decided that this was a good place to start, since so many problems seem to be associated with these chips.
Fix - Reflow
Using some suggestions and timing from http://www.youtube.com/watch?v=vR8L3B3eDr0 , I re-flowed the two chips on the board that were BGA. The ribbon cables mostly come off with a release of some sort, except the black cable in the mid-lower right of this picture. 5 or 6 wire, i don't remember which. It seems you have to cut and re-strip this cable. Once cut, you can remove the cover assembly and release the pins that lock the wires in place. On all single strand wire cables, note pin 1 is marked on the cable and on the board.
The others on the board that look similar have a raised/spring loaded portion that can be pressed on to release the cable.
The medium-wide silver cable has release tabs on either side.. press both to release.
The wide white cable simply pulls out of the socket its in, but is stiff. Be careful!
Fix - Longetivity (and additional notes)
It has been reported that there is a voltage problem on this board and that any fix you make will be temporary unless you add a smaller board that regulates the voltage of the board .1 volt lower.
I did this fix about 1 year ago today, and it worked perfectly until I added the fan. in process of adding the fan i bend the board more than i would have liked, and lost the functionality of the on screen display. Since then, I have had no other issues (other than slow HDMI sync.. but it always works. Just takes 30 seconds sometimes)
There is a PDF on this AVS forum thread that shows the voltage regulator addition board that onkyo prescribes as part of the fix for this board.
While working on the amp, i noticed how much heat got trapped under the HDMI board.
So in an attempt to help the reflow last longer, I added a fan and small heatsinks using thermal tape to the two chips shown above.
The fan I used was an extremely low noise / low current fan, and I simply t'd it into the fan wiring for one of the side fans. Hasn't failed yet- so hopefully running the two fans in parallel wont' cause too much current draw on the fan driver and cause it to fail, heh.
Here is a slideshow to some pictures:
Some other (dis)assembly photos
AVS forum page for this amplifier with lots of good hints and discussion about issues: http://www.avsforum.com/t/1192172/the-onkyo-tx-nr3007-tx-nr5007-common-questions-issues-hints-answers-thread
Youtube video used for timing on fix: http://www.youtube.com/watch?v=vR8L3B3eDr0
My posting on the AVS forum thread: http://www.avsforum.com/t/1192172/the-onkyo-tx-nr3007-tx-nr5007-common-questions-issues-hints-answers-thread/4560#post_22426872