Does this problem with my amplifier make sense?

Discussion in 'AV Receivers' started by Steve Elias, May 31, 2005.

  1. Steve Elias

    Steve Elias Stunt Coordinator

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    All of a sudden my Rotel RB-985 Mk II 5x100 amp is overheating (I noticed because the audio began distorting and cutting out), but only when the DVD player is the active source. The amp apparently works fine when the satellite is the source. I assume this makes sense, but nevertheless I was surprised by it. I have an email in to Rotel, but while I wait for an answer I'd appreciate any insight you might have. Given the extremely minimal amount of info I've given you, is it possible to know if the problem lies with specific part of the amp (resistors and so on)? Also, is there any general rule of thumb for amp repair, as there is with CD players where most are chepaer to replace than to repair? Thanks.
    -Steve
     
  2. Paul Clarke

    Paul Clarke Supporting Actor

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    How about a little more info?

    Are you using the DVD player for CD play as well? If so, does the amp act up then? At what volume? Or have you noticed a volume level relation at all?

    If this is strictly related to DVD play, same questions.

    What speakers are in play?
     
  3. John Garcia

    John Garcia Executive Producer

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    If it doesn't happen with other sources, I would not suspect it is the amp. Does the amp actually feel HOT to the touch when this happens? If not, it may not be the amp that is causing the dropouts - it sounds like it may be your player. As Paul asked, does it do it at any volume?
     
  4. Robert Cowan

    Robert Cowan Supporting Actor

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    last time i opened one up, those rotels has a heat sensor attached to the heatsinks and back to the main board. they will probably go into protect mode way before they will overheat and distort. i also think its the source, not the amp. its very very very hard to get one of those rotels to overdrive itself unless you are just seeing how loud it can go.
     
  5. Steve Elias

    Steve Elias Stunt Coordinator

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    Thank you all for the help. I apologize for the delayed response; I had a minor emergency that kept me away from the computer.

    Paul's questions:
    Are you using the DVD player for CD play as well? A: Yes.

    If so, does the amp act up then? A: It hasn't acted up in the past, but I haven't used it as a CD player after the problem first occured while in DVD mode. I'll fire it up, hopefully not literally, and return with the rest of the answer ASAP.

    At what volume? A: Normal volume(?), I'm guessing 50-60 decibels. It certainly wasn't loud by any traditional standard.

    Or have you noticed a volume level relation at all? A: No.

    If this is strictly related to DVD play, same questions. The answers above apply to DVD play. I'll return shortly with the effects of CD play.

    What speakers are in play? A: Two full range JBL mains, and a Polk center channel.

    John's questions:
    Does the amp actually feel HOT to the touch when this happens? A: Yes, it is noticably hotter to the touch.

    As Paul asked, does it do it at any volume? A: I'll double check, but the the preliminary answer is yes as it was overheating during DVD play at normal to low volumes.

    Robert's comment:
    They will probably go into protect mode way before they will overheat and distort. A: Yes, I did notice the protection lights flickering on, but my attention was first drawn to the amp by a sudden mix of sound dropout and distortion.

    Thanks again for all the help. I must admit I hope the consensus is born out by my comments as I would much rather replace my four year old inexpensive Toshiba DVD player than repair or replace the Rotel amp. The Toshiba is clearly the weakest link inmy system anyway.
    -Steve
     
  6. Steve Elias

    Steve Elias Stunt Coordinator

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    One more item: The amp doesn't heat up instantly during DVD play; it seems to take 45-60 minutes to reach problem levels.

    -Steve
     
  7. LanceJ

    LanceJ Producer

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    If this amp is only overheating when the dvd player is being used for a signal source, that's really weird.

    But..........

    Possible scenario #1: Maybe the dvd player--or the receiver's Dolby/DTS decoder--is malfunctioning and sending some type of irregular signal to the amp, causing it to act that way? Since it's becoming hotter, this could mean some kind of subsonic bass signals or nasty high frequency ultrasonic ones.


    Possible scenario #2: Steve, are you using a powered subwoofer in your system? If you aren't, that would mean the Rotel is being used to power those large front mains that are also handling extreme low bass signals that are present on certain dvds AND if a lot of adventure movies with lots of low bass effects are played, that could be part of the cause of the extra heat generation, and clipping too if turned up to really loud levels.

    But IMO it's not the amp that is the problem here.
     
  8. John Garcia

    John Garcia Executive Producer

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    I'd still check all wiring for shorting somewhere. A single stray strand could cause this sort of thing.

    What are you using as a pre/pro?

    What speakers?
     
  9. Grant B

    Grant B Producer

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    Are the two units powered from the same outlet or off the same circuit breaker?
    If so try and take the amp off and put it on a breaker with little else.
     

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