My NAD T743 working only in stereo listening mode. All modes ar disappeared. In setup is only stereo listening mode and if push surround button, nothing happen - its work only in stereo

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https://nadelectronics.com/software/

https://nadelectronics.com/wp-content/uploads/2017/02/T755-English.pdf

Dolby Pro logic is a mode that works off the stereo signal for Pro logic mode. It takes the out-of-phase signals and send those to the rear and stereo signals to the sides and mostly mono from the center Channel. If the audio Source you're listening to is mostly mono then you will only hear The center Channel. there's nothing wrong, you just need a wide range stereo signal to get surround and best if it was recorded in Pro logic

Most problems are menu settings, because surround modes can be complex and confusing. Verify what surround input type you are using. FM tuner will not play center spkr unless put into a simulate or expand stereo mode. Do other surround speakers work other than normal L/R stereo mode? You can try redoing your auto surround setup (MCACC) or going to the manual speaker setup and verifying speaker is turned on in menu system. Rechech you listening mode setups at Pages 33,38,39 in your manual. Try another speaker and wiring on center output. Try Different surround inputs, some manufactuers have had problems with their DTS and HDMI boards. Otherwise take to repair.

Have you looked at the manual? There is no internal source that would produce 7.1 audio other than the test tones. Attach a multichannel source according to ITS manual.

Register and download the manual for free at retrevo.com

http://www.retrevo.com/support/NAD-T763-Receivers-manual/id/8043bh646/t/2/

Hi, have you checked the power button in the back to see if it got pressed by accident? It's a round button located right under the speaker inputs in the back.

LCD will display which speakers are active. And this depends on 2 things: the source signal and decoder mode.
If source signal is stereo, only front L+R speakers are used. For 5.1 signal (for example DVD over HDMI / optical/coax spdif) all speakers installed (which are not set to None) are used.
To listen to stereo input signal using all speakers, switch decoder to enhancer mode.

try to calibrate the speakers from audessy rom menu,i did it and it lokes like it just needed to register all the channels,hope it helps.

The reciever you have has 5.1 inputs at the backof it.The only way to get Dolby True HD and DTS HD is to run the 7.1 analog out from the bd55 to the nad. You'll have to leave the 2 rear surround open on the bd55 leaving the remaining 6 connected to the nad. The digital coax and the optical will not transmit the hd data, only the analog out will. Run a hdmi right to your HD tv for picture bypassing your amp. this will workfine and you'll have the audio you want. You,ll have to change the input settings for dvd in your amp to 5.1 to recieve the audio.

To reset the the T743 hold down the video 6 and the source up buttons for 3 seconds. then power up from the back button

NAD Technical Bulletin T743-H2005-06 describes the problem "Unit may shut down, shortly after turn on".  Reason: There is a diode on the standby board that maybe operating intermittently.  Solution: Locate and identify D756 on the standby board.  Change only if the diode is a 1N4148.  Change from a 1N4148 to a 1N4004 or equivalent.  
It is located near a transformer and some fuses.