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Stereo Amplifier fades out. My Sansui dolby pro

Stereo Amplifier fades out. My Sansui RZ-2200AV dolby pro logic surround sound amplifier has stopped working properly. Sometimes when I turn it on, it will work for a few seconds before the volume fades out slowly with a fuzzy sound as if it's losing power. Sometimes it just won't work at all. I've tried different inputs, even using the built in FM receiver, all sources respond the same way.

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  • contact556 Dec 14, 2009

    Why thankyou :) I pride myself on my troubleshooting abilities! The sound comes on with a slight delay with power on. I tried it again yesterday and it was fine for about 15 minutes then there was a slight pop noise and it faded out quite quickly (too quick for me to notice if there was a fizzle noise).

    I just tried it again after 24 hours rest, and it was no good. This time I used an iPod to RCA connector. The sound was immediately very weak and "fizzy" like I was half-tuned into a very very weak AM radio station. Yes it is both Left and Right (that's all I've got connected at the moment). Thanks for your help.

  • contact556 Dec 26, 2009

    OK, great tips - thanks.
    It is not intermittent anymore.

    I've tried using headphones - same issue.

    I've tried using the test tone and cannot hear it. So it is affected too. (The test tone is a kind of white noise anyway, so it'd be hard to tell in the tiny, faint, crackly noise I can hear in the speakers).

    I've tried monitoring with tape out, and lo and behold - I can hear both FM radio clearly and also playing an iPod through the Amplifier. So, that seems to indicate something in the power amplification circuitry, correct?

    Lastly, I've fiddled with balance and treble and bass, as well as all surround settings and there is no change, so I guess that rules out a dodgy switch or pot too?

    Thanks so much for your help so far!

  • contact556 Dec 26, 2009

    Ah, already disconnected all speakers. Sorry, I forgot to mention I did that. Just retried connecting only one speaker at a time, and also swapping left with right just to be doubly sure.

    There is an overload indicator, but it is not on.

    To clarify regarding the 'pop'. I had never heard the pop previously when the amp had died out before, or since. Just that one time. But since that one time, the very low crackly volume has been an constant issue, rather than intermittent.

  • contact556 Dec 26, 2009

    Awesome. Thanks for your help. I'm going to crack it open myself to see if it's obvious. Then hopefully save myself some cash!

    You've been a great help. Thanks again.

  • contact556 Dec 31, 2009

    Interesting update:
    Opened it up and had a look. No caps had that obvious bulging look, however there was one on the power source circuit board that had dried up brown stuff on one side and onto the board - however I understand this is probably more likely to be old glue.

    I wiggled it to check and it did seem to move a little bit more than others.
    A little while later I tried the amp and it worked again for a bit.
    However the next time it didn't. But here's the interesting bit: when I pressed the power button in (which is a physical button that has a mechanical connection to the actual button back on the power source circuit board), to turn the amp off - it suddenly sprang to life again. To me, that sounds like there's maybe a cracked solder joint on that board, does that sound reasonable?

  • contact556 Jan 04, 2010

    Well...Final update: I finally found the problem; a couple of cracked solder joints on a couple of resistors on the power supply circuit board! Almost impossible to see, but I could see a little heat discolouration in that area and pushing various areas with a pencil - tracked it down. Reflowed the solder and added a touch more and it's all good now! Since then I've found out I can't run audio direct to it while watching my new LCD anyway because of the dreaded input lag with HD screens! Argh!.

    I want to thank you for your excellent help and patience in narrowing this issue down. You gave me the confidence to do it myself. Cheers.

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  • 8,546 Answers

No that's how to describe a problem, folks - with details. Using internal FM as the source is always the preferred way of troubleshooting system-wide receiver audio problems (no cables or setting in the way).

Does the sound come on immediately with power and then fade or is there a small delay while the electronics stabilize, a click and then sound that fades?

The fizzle probably means something is rapidly overheating or a capacitor is malfunctioning. If both channels do it, I'd suspect a common power supply problem. Can't help much more than that.

Posted on Dec 12, 2009

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  • 2 more comments 
  • David Dunn
    David Dunn Dec 15, 2009

    The worst problems are the intermittent ones.



    Continue monitoring for some sort of pattern. We know the effect, now we need to find a cause.



    That it stays up for some time might help. The slight pop might be the result or the cause of an impulse kicking something over the razor edge on which it teeters.



    Okay, we're still on the track of a component or internal signal path malfunctioning over some random time. It's now starting to sound like a connection or circuit slowly failing.



    Staying with internal FM, manipulate controls and switches on the amp.



    Do you have a tape deck? Connect it to the Tape Out and monitor the level meters when it fails. If the sound drops to the Tape Out jacks that lets out the amplification circuitry and narrows it down to a signal path problem. THAT would cut the problem diagnosis in half.



    If the signal is still is still present but not audible at the speakers it's in the amplification path but still possibly in tone or balance controls.



    I see online there's a Test Tone. Set that up when the unit is working and determine how far it goes through the receiver. You could quickly substitute it as the source when the unit fails. I suspect it would bypass the internal tone controls so its audibility might help to further isolate the failure.

  • David Dunn
    David Dunn Dec 26, 2009

    In reviewing what we have so far I just noticed you mentioned a pop (Dec 14) preceding the loss of volume. I'm not familiar with how this unit reacts when it goes into speaker protection mode or if it has an indicator to tell you it's active. Most just crowbar the output by dropping a relay (click), perhaps yours produces a fizzle and goes silent until the perceived problem clears up.



    When you normally power up the receiver did it have an audible click a few moments afterward, indicating a protection relay energizing to enable the amps? If so, does it still click even in failure mode?



    Internal problems would most likely be caused by excessive current or heat. I doubt it's heat because you now have a solid problem that apparently appears as soon as you power it on.



    Let's eliminate speaker shorts as a problem. If the problem is solid turn it on, adjust the volume control to a low-normal setting (just in case it comes back to life) and start disconnecting or disabling speaker sets. If the amp suddenly comes back we have an external problem like a shorted speaker wire.

  • David Dunn
    David Dunn Dec 26, 2009

    OK. I think surgery is needed now. You probably heard a power capacitor give up the ghost.



    For diagnostic purposes and to satisfy your own curiosity (you're on the scent now), you could go inside and look for a blown component. Big caps typically look like little batteries.



    Unplug the unit. NEVER touch a capacitor with your bare hands before discharging it by shorting the contacts.



    They don't always exhibit external evidence of having blown. A trip to the shop would be the next step since the problem is solid now. They should find it quickly.

  • David Dunn
    David Dunn Dec 31, 2009

    Tally Ho!



    I think you are HOT on the trail, however, tread lightly around suspicious power connections, do most of your physical contact troubleshooting with power off, being mindful of the dangers not only to you but to the components should you suddenly experience rapid make/break of a contact.



    That brown dried up stuff could be electrolyte from a blown cap. I'd look a bit closer at that, too.

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