I get an error code 31 when I try to auto cal the speakers on my str dg910 reciever

SOURCE: STR--DG910: no rear speaker sound, no center speaker sound

if you confirmed all connection repeat your speaker setup.

SOURCE: I HAVE A SONY RECIEVER STR-DH700, I get no sound

make sure the FM antenna is connected and in a good place then check to see if the A-B speaker selector is selected properly.check to see that the sound field is set properly, My 800 allows for several different options and if your speaker wires are reversed or not in the correct position front left at front left etc it will not send the signal to those speakers. try using the TEST TONE feature if you have one it will send a signal to each speaker in sequence (LF< C< RF<in order) it will go all the way around to see if they are connected properly, that way you can tell if they are connected at all or in the wrong spot on the back interface. I dont know if that is what you meant by AUTO CAL, but that is a seperate feature when you use the connected mic to determine range, height and distance to the position in the room you are most likely to be seated for optimal sound.

SOURCE: When I try to auto

RTFM (refer to the manual) Page 44.
None or only one one of the front speakers are connected (as detected by the microphone).

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http://www.retrevo.com/support/Sony-STR-DN1000-Receivers-manual/id/23411ag516/t/2/