is my NAD t752 on the fritz?

Discussion in 'AV Receivers' started by ChrisSanders, May 10, 2003.

  1. ChrisSanders

    ChrisSanders Auditioning

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    Hi all,

    I've been lurking here for a while, and you folks have been a tremendous source of information. After weeks of contemplation, I finally decided to invest in a T752 and a set of Cambridge Soundworks Newtons.

    Until recently, they've served me well. But about a week ago, while listening to a Dolby Surround source (Super Mario Sunshine, to be precise [​IMG] ), it sounded like the center channel dropped out. I threw the Avia DVD in, and sure enough, the center channel was kaput.

    Strangely, tho, it wasn't completely gone. The signal was there, but it was very faint and accompanied by prominent (but quiet) hiss.

    Naturally, I set about troubleshooting. I checked all the software settings, and verified that the center channel was activated, +0db, etc. Unfortunately, everything there was exactly where it should have been, so I moved to hardware.

    I started with the easy one, a full T752 power cycle. No dice. I tried to isolate the failure by swapping the right-main and the center speaker cables at the rear of the receiver...the results were as expected, with the right-main now playing the nearly silent center feed and the center speaker playing the fully functional right feed. This essentially vindicated the speaker and its wire, leaving only the receiver (or the connections thereto) to blame. Frustrated, I rewired the right-main, shut down and unplugged the receiver, and went to bed.

    The next morning, I rewired the center speaker and re-activated the receiver, and the center channel was fine.

    I wasn't sure what it was, exactly, that had worked this particular voodoo (Rewiring? Unplugging? Happy thoughts?), but I was happy enough to have my center back that I didn't dwell too long upon my flagrant disregard for the scientific method.

    Two days later, however, the center channel disappeared once again. This time, I fast-forwarded through the sequence from before...power cycle, swap cables, replace cables...viola! Center was back. I was starting to think that the physical connections at the back of the box were the problem...a loose connection would explain the reduced signal strength and intermittent nature of the failure, especially considering everything worked fine after a fresh connection. I glared accusingly at our feline roommates, tightened the wires down extra tight, and once again thought it resolved.

    But tonight, it happened again, and I'm started to think there may be a glitch in the receiver. In an attempt to disprove my "loose connection" hypothesis, I'm making a run to Radio Shack tomorrow for banana plugs (I have less and less faith in my ability to make blind wire connections). If, in fact, that doesn't work, do any of you folks have any idea what else could cause the center channel to become so weak (and sometimes disappear altogether)? Any input would be appreciated. Other useful info:

    - Center sound is audible, but quiet and crackly.
    - Symptoms persist across multiple input sources, both analog and digital.
    - Detaching and re-attaching speaker wires at receiver terminals sometimes fixes the problem for a day or two.

    Has this happened to anyone else? Are there other possible causes I'm overlooking?

    Thanks all,
    -Chris
     
  2. Rich Wenzel

    Rich Wenzel Supporting Actor

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    sounds like the amp or the terminal section of the NAD is not working properly, however, you don't say which modes that you tested this for...

    did you try all multi-channel modes? DTS, dpl2, dpl, dts:neo6, EARS, etc??

    if the center channel works on some of the DSP's and not others, then it is possible that it is some processor problem...

    Rich
     
  3. JamesHl

    JamesHl Supporting Actor

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    If the banana plug doesn't work, take it in. Perhaps the amp for the center channel is screwed up.
     
  4. Chu Gai

    Chu Gai Lead Actor

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    could be a bad solder joint inside the Nad that leads to the center channel if it's not the wires. no chance that you're playing the unit too loud and it's going into some kind of protection mode until internal temperatures stabilize?
     
  5. ChrisSanders

    ChrisSanders Auditioning

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    Thanks for your replies, folks. I bring news.

    All connections are now banana-plugged, but the problem is still there. In any situation, a full power cycle temporarily fixes the problem.

    The problem exists in all modes, and is often (though not always) triggered by switching between sources of different modes (DTS DVD to Dolby Digital 5.1 TiVo, or Dolby Surround GameCube to Dolby Digital 5.1 DVD).

    With that in mind, I was leaning toward a processor glitch of some sort...but after letting Stop Making Sense run for a bit, David Byrne just dropped out, unprompted. And right in the middle of "Thank You for Sending Me an Angel". Disheartening on so many levels. [​IMG]

    I thought it may be heat related (since it fails after a certain length of time), but the unit has plenty of ventilation and isn't driving that much that loud.

    So alas, it looks like a call to NAD is in order come Monday (or perhaps an e-mail tonight). It's still under warranty...in fact, my current unit replaced my original, an early revision with a digital input glitch. I'm tempted to pop it open and see if there's a dangling wire somewhere, but I fear voiding the warranty. Hopefully they'll ship me a replacement here so I won't have to drive two hours back to the dealer =(.

    On the bright side, I hear there's a new revision out that quiets the fan, shortens the awkward "digital pause", and adds some configuration options. Maybe this is a blessing in disguise...I've always wanted to name my inputs [​IMG].

    -Chris
     
  6. NickSP

    NickSP Supporting Actor

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    The NAD T752 had a lot of problems initially and in my use of the NAD 752 as a prepro, I encountered many of them. One of them was similar to yours but through the preouts. My right surround channel would frequently give up on me and if I shut the receiver off and then back on again, it would be fine for a couple of hours. I promptly sent the NAD back but I am told by my dealer that NAD has fixed a lot of the 752s problems. While it worked, it made a fanrastic prepro and I absolutely loved the presets and the 2 channel music.
     
  7. JamesHl

    JamesHl Supporting Actor

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    Naming the inputs is awesome, the first time my friends came over to play halo after I got my 762 they said "it can recognize your xbox? wow!" [​IMG]
     
  8. Jonathan M

    Jonathan M Second Unit

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    Chris -

    Which version T752 do you have? Hold down the Audio and Video front panel buttons simulataneously and it should show you. Mine is v1.06 A7 for reference. Apparently there are A6 versions also out - don't know which is newer. I should be getting my software upgrade within a week or two - just waiting on the shipping to New Zealand.

    Your problem will likely be a processor issue - you can check the amp section of the centre channel by removing the pre-out main-in jumpers and connecting the left pre-out to the centre main-in. Then hook the centre pre-out to the left main-in. Now the problem should be in the left channel if it is a processor issue. Otherwise it'll be an amp problem.

    Hope this helps - please let us know how it turns out. I have had no problems with my unit other than the volume "tick" thing and digital mute which is fixed in the software upgrade.

    Cheers,
    Jonathan
     

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