Originally Posted by mindbomb
Valence01 & All who can help:
I have a Xbox360 premium from September 2008
I tried connecting the HD cable and HDMI to get 5.1 optical out to my receiver and video on the HDTV. After I realized it is getting reset each time I switch TV input and return to the Xbox HDMI input I removed the jumper 26-28 on the HD cable and got no sound at all (only on HDMI, no optical).
It is the bulky cable with the SD/HD switch. I tried it in both ways - both no sound, video, analog sound -nothing on HD cable.
I checked with a multimeter and I saw that on my cable the SD/HD switch actually jumpers pin 20 and 24 to GND when on SD and 24 to GND when on HD..
What's the thing here? Why I get no optical sound output and everybody else does with same cable and config?
That is an odd cable indeed. The standard HD AV cable grounds 20 and 24 in SD position, with 28 permanently grounded. In HDTV position, the switch disconnects the ground to 20 and 24, but leaves the hard-wired ground on 28. Normally 20 and 24 are tied together and then to the switch. What you descibed where 24 is still grounded in the HDTV position, will definitely result in no optical audio. When I tried that combo, not only did I not get optical audio, I did not get HDMI video, nor component video, though analog audio did work. Kinda useless. In any case, to get HDMI video with optical audio and no reboot issue, you want both 20 and 24 grounded and 28 not grounded. So, put the switch in the SDTV position.
I don't know how to make a table on this forum, else I'd show all 8 possible gnd/not gnd options for the 3 pins and what the results were. Suffice it to say, that there is only one useful combination (20 and 24 gnd, 28 not gnd) and this is exactly what the Microsoft audio dongle does. Other combinations do various things, that are generally more annoying than useful.
Edit: Ok it's not a table, but rather a picture of a table. Here it is anyway:
An 'x' means connected to gnd for that pin, while an 'o' means left open. Keep in mind that an HDMI connection always takes precedence. That is, if you have an HDMI cable connected from the 360 to a working HDMI display, it will always over-ride any other jumper settings. The column labeled 'reboot issue' indicates whether this jumper setting will have the reboot issue when using an HDMI connection.