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Old 8th July 2007, 01:40 PM   #1
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Default Unstable volume problem

Hi:

My dad has a Onkyo A-809 integrated amplifer that has a volume unstability problem. Sometimes the volume increases by itself by a lot. This gets sorta annoying at times. What's the problem?
Could it be the power supply capacitors? Any help would be greatly appreciated!

Allen
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Old 8th July 2007, 01:51 PM   #2
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Location: Canandaigua, NY USA
My vote would be for dirty switches or potentiometers, especially if the problem is different between the channels. Protection relays can also develop dirty contacts and cause similar things. Get some spray tuner cleaner and squirt a bit into each switch and control, working the knobs as you do so. Put paper towels around so you don't get any of the cleaner on anything else. It can reduce the life of capacitors if it gets past the seals. Usually, if a problem is identical on both channels, look at the power supply. If it's different, suspect something else. Can you tell if it's common, or if it's associated with any particular switch positions? Also, if the thing has a "pre out/amp in" shunt or switch on the back, clean that as well. I recently serviced an amp where that switch on the rear had a blocking plate so it couldn't be accidentally switched. It got intermittent- an easy fix that the owner could have done, had he removed the blocking plate.
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Old 8th July 2007, 02:27 PM   #3
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I'm positive that the problem happens at the same time on both channels. Switches does not affect the problem. There aren'tany pre/out switches in the back for sure. The only thing that I'm worried about is the problem leading to the power transformer because that would be very hard to replace. One thing that could have caused this problem is because of the excessive heat at the place I'm living (ignore the Canadian flag cause I'm on vacation) and the place sometimes have unstable power. Has no one had this problem before? My dad also owns an Audiolab preamp/amp which has the same problem but not as serious. I hope this could be cheap fix. Thanks
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Old 8th July 2007, 02:34 PM   #4
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Well, if it's common to both, you need to attach a meter, or better yet, a scope, to the power supply and look at it. Almost all amps use symmetrical supplies, though there may be some secondary supplies as well. First, see if the available voltage is consistent with the power rating of the amp, and if it's stable and reasonably ripple free. Having a second piece of equipment with the same problem is really odd/suspicious. Are you really close to any radio transmitters? Check your sources as well. If the supply doesn't pan out, apply a fixed signal and trace it from the input. A schematic would be a great help if you can find one.
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Old 8th July 2007, 03:13 PM   #5
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I could use a meter to see if the power supply is stable. How would I check if it's ripple free (I'm not even sure if I know what ripple free means)? Sorry, but I don't have a scope and don't know how to use one. I don't think I'm close to any radio frequencies. One thing that I do remember though was that the audiolab used to be in our house then later replace by the onkyo. While the audiolab was in the house, it developed the volume problem. Then when it was moved to my dad's workplace, it seem to improve and I don't think it ever happened again. And the Onkyo didn't use to have this problem until it was used constantly in our house. Could it have anything to do with living on the highest level of our apartment? I don't know, but it could be because of all the people that are using the power that is already quite unstable at times on the apartment that is affecting the power of our home. That is just a thought though, nothing more. Come back and check this thread in the next two days cause I'm gonna check the power supply. Thanks
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