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Re: [Electronics_101] Yamaha AVX-20 stereo receiver problems

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  • Robert Graf
    ... From: jon To: Sent: Sunday, March 31, 2002 9:49 PM Subject: [Electronics_101] Yamaha AVX-20 stereo
    Message 1 of 13 , Mar 31, 2002
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      ----- Original Message -----
      From: "jon" <jon@...>
      To: <Electronics_101@yahoogroups.com>
      Sent: Sunday, March 31, 2002 9:49 PM
      Subject: [Electronics_101] Yamaha AVX-20 stereo receiver problems


      >
      > I have a nice Yamaha AVX-20 that has a "power problem". When it is turned
      > on, a relay inside clicks on and off, forever. It appears that the relay
      > is some some of protection system (to cut off power to the final
      > amplifier).
      >
      > In fact, this problem blew out a woofer in one of my speakers. I checked
      > the final output transistors, and they ohm out fine.
      >
      > Can any one venture a guess as to what is wrong...or, point to a me a
      > source for schematics?
      >
      > Thanks!
      >
      > Jon
      >
      I would guess you are correct about the relay being associated with output
      protection. Whether it disconnects the speaker or shut down the power amp, I
      can't say. You should really get a copy of the schematic and see what the
      protection circuit is monitoring. How did the woofer blow? Was the amp
      cranked? Do you have a low filter? A cranked amp will blow up up a much
      higher power rated speaker if the power supply filter caps get drained by
      trying to pump too much power. Since it is the woofer that blew and not the
      xover or midrange or a tweeter, I will guess that one or more output
      transistors shorted collector to emitter. How did you check the output
      transistors? The base-collector junction should have slightly lower
      resistance than the base-emitter junction when forward biased. When reversed
      biased, they should look open as should the emitter-collector in both
      directions.
    • jon
      ... The cone was damaged by too much movement. ... The volume was moderate , not anywhere near cranked. ... No ... With a DVM in diode mode. Checked
      Message 2 of 13 , Apr 1, 2002
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        >How did the woofer blow?
        The cone was damaged by too much movement.

        >Was the amp cranked?
        The volume was "moderate", not anywhere near cranked.

        >Do you have a low filter?
        No

        > How did you check the output transistors?
        With a DVM in diode mode. Checked BE,EB,etc.

        Every now and then, the amp will come on without cycling the protection
        relay.

        Looked at the 50V power rails on a scope, and there was a little bit of
        ripple. Don't know if it was an acceptable amount.

        This may be something as simple as power supply capacitors.

        Any thoughts on a source of schematics?

        Jon
      • SexyBrian1979@aol.com
        Your 50v supply has ripple? Hmm. Wether this is acceptable or not, really depends on wether the 50V rail is a stabalized rail or if it s unstabalized. If it s
        Message 3 of 13 , Apr 1, 2002
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          Your 50v supply has ripple? Hmm. Wether this is acceptable or not, really
          depends on wether the 50V rail is a stabalized rail or if it's unstabalized.
          If it's stabalized, it should be a fairly straight, if not dead straight DC
          line. If you suspect this is your problem, then change a few of the high
          capacitance Electrolytics on the 50V rail

          Brian
        • Gary
          I have been in car stereos in the past and can tell you only two things I have ever seen will cause this.. 1. Too much power in the wrong enclosure i.e.: open
          Message 4 of 13 , Apr 1, 2002
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            I have been in car stereos in the past and can tell you only two things I
            have ever seen will cause this.. 1. Too much power in the wrong enclosure
            i.e.: open air or port too large 2. DC current.
            ----- Original Message -----
            From: jon <jon@...>
            To: <Electronics_101@yahoogroups.com>
            Sent: Monday, April 01, 2002 3:16 PM
            Subject: Re: [Electronics_101] Yamaha AVX-20 stereo receiver problems


            >
            > >How did the woofer blow?
            > The cone was damaged by too much movement.
            >
            > >Was the amp cranked?
            > The volume was "moderate", not anywhere near cranked.
            >
            > >Do you have a low filter?
            > No
            >
            > > How did you check the output transistors?
            > With a DVM in diode mode. Checked BE,EB,etc.
            >
            > Every now and then, the amp will come on without cycling the protection
            > relay.
            >
            > Looked at the 50V power rails on a scope, and there was a little bit of
            > ripple. Don't know if it was an acceptable amount.
            >
            > This may be something as simple as power supply capacitors.
            >
            > Any thoughts on a source of schematics?
            >
            > Jon
            >
            >
            >
            > To unsubscribe from this group, send an email to:
            > Electronics_101-unsubscribe@yahoogroups.com
            >
            >
            >
            > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
            >
            >
          • Robert Graf
            ... From: jon To: Sent: Monday, April 01, 2002 3:16 PM Subject: Re: [Electronics_101] Yamaha AVX-20
            Message 5 of 13 , Apr 1, 2002
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              ----- Original Message -----
              From: "jon" <jon@...>
              To: <Electronics_101@yahoogroups.com>
              Sent: Monday, April 01, 2002 3:16 PM
              Subject: Re: [Electronics_101] Yamaha AVX-20 stereo receiver problems


              >
              > >How did the woofer blow?
              > The cone was damaged by too much movement.
              >
              > >Was the amp cranked?
              > The volume was "moderate", not anywhere near cranked.
              >
              Was the voice coil thrown out of the gap? When you said that the woofer was
              blown, I figured you meant that the voice coil was burned. I don't
              understand how too much cone excursion could happen if the amp was not
              turned up. Low frequency transients can cause this. How long are the speaker
              wires? I've seen some huge cone movements caused by people waing across the
              floor where the speaker wires were. The low filter took care of this. What
              is the impedance of the speaker? Are the spaekers matched to the amp? A 2 or
              4 ohm speaker hooked up to an output rated for 8 ohm speakers will put out
              full power even when the volume control is not turned up all the way. Also,
              if the input source has a high enough level, full output (or greater) will
              occur even if the volume control is not full up. What was the signal source
              that caused the woofer failure?

              > >Do you have a low filter?
              > No
              >
              > > How did you check the output transistors?
              > With a DVM in diode mode. Checked BE,EB,etc.
              >
              > Every now and then, the amp will come on without cycling the protection
              > relay.
              >
              So, the amp does work, just intermittently? Unfortunately, these problems
              are the toughest to figure out. If the amp does work periodically, the
              transisor check was probably unnecessary. You'll need to see what the
              proection circuit monitors and check those sources out. It should look for
              dc on the output and overpower conditions at the least. It might also be
              used to prevent turn-on/turn-off transients, but plenty of amps don't
              require that.

              > Looked at the 50V power rails on a scope, and there was a little bit of
              > ripple. Don't know if it was an acceptable amount.

              Probably nomal. If you're not getting hum, then it's probably ok.

              >
              > This may be something as simple as power supply capacitors.

              If you observed the power supply rails with a scope and didn't see anything
              but ripple, I doubt that a ps cap would be the culprit. If you measured the
              ripple with a dvm, you don't know what you have. You could be getting some
              short duration spikes don't register much on the dvm.
              >
              > Any thoughts on a source of schematics?

              How about the manual? Have you tried the Yamaha site?

              >
              > Jon
              >
              >
            • Robert Graf
              ... From: To: Sent: Monday, April 01, 2002 4:16 PM Subject: Re: [Electronics_101] Yamaha AVX-20
              Message 6 of 13 , Apr 1, 2002
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                ----- Original Message -----
                From: <SexyBrian1979@...>
                To: <Electronics_101@yahoogroups.com>
                Sent: Monday, April 01, 2002 4:16 PM
                Subject: Re: [Electronics_101] Yamaha AVX-20 stereo receiver problems


                > Your 50v supply has ripple? Hmm. Wether this is acceptable or not, really
                > depends on wether the 50V rail is a stabalized rail or if it's
                unstabalized.
                > If it's stabalized, it should be a fairly straight, if not dead straight
                DC
                > line. If you suspect this is your problem, then change a few of the high
                > capacitance Electrolytics on the 50V rail
                >
                > Brian
                >
                I'm not sure if stabilized refers to filtered or regulated, but a typical
                stereo amplifier would not have a regulated supply for the power amp. If it
                did, the output voltage would either be correct or zero volts. I suppose it
                could be cycling on and off if the protection circuit was intermittent. The
                50v rails are probably only filtered and some ripple is normal as the output
                stage is most likely common collector which is pretty gain independent with
                regard to collector-emitter voltage variation. I don't think changing any of
                the filter caps will do anything. If one of the caps opened, there would be
                a lot of ripple as very few amps use multiple filter caps on any power rail.
                If the cap shorted, tere wouldn't be any voltage on that rail.
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