Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Problem?

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • JimBanville
    Senior Member
    • Aug 2020
    • 118
    • United States

    #1

    Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Problem?

    So I didn't realize there was a tiny written warning on the speaker impedance switch on the back that said moving the switch with the power on "may damage the unit". I actually switched it multiple times, listening for any possible audible changes. It wasn't until later I saw the tiny warning. I haven't noticed any issues though. Can someone please look at the schematic and tell me what damage I may have caused? Thanks!!

  • R_J
    Badcaps Legend
    • Jun 2012
    • 9535
    • Canada

    #2
    Re: Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Probl

    If the amp is still working, you are ok, just don't switch it when the amp is on because you could damage the output transistors and maybe more.
    in this case you got lucky. The service manual is too blurry (low res.) to read. I don't know why people do this to service manuals.
    Last edited by R_J; 01-25-2021, 10:46 AM.

    Comment

    • JimBanville
      Senior Member
      • Aug 2020
      • 118
      • United States

      #3
      Re: Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Probl

      Originally posted by R_J
      If the amp is still working, you are ok, just don't switch it when the amp is on because you could damage the output transistors and maybe more.
      in this case you got lucky. The service manual is too blurry to read
      Thanks! At work now so I can't get a good look at the service manual. I'm on my phone. I was going to find the specific pages with the power supply, etc and post them. I'll try when I get home
      Gotta say tho...hey, Yamaha...why not make the switch recessed like the voltage selectors often are? A switch projecting out could get bumped while moving or cleaning the unit. At least then you would have to be looking at the back of the unit to change it and are likely to see a BIG warning! Haha
      Last edited by JimBanville; 01-25-2021, 11:00 AM.

      Comment

      • Khron
        Badcaps Legend
        • Sep 2006
        • 1350
        • Finland

        #4
        Re: Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Probl

        You might be able to see a bit more in a non-mangled version of the service manual:



        There's a slide switch on the bottom-right of page 47 (containing the power amps), that goes to a signal called "8/4" going to the microcontroller, and a "/4ohm" signal coming back to the power board. That seems to drive some opto-controlled triacs(?).

        I've got a hunch those just alter the amplitude of the supply rails (lower voltage for the lower impedances, higher voltage for the higher impedances), so as to keep the required current about the same.

        I doubt flicking that switch would do much (or anything) if you weren't passing any signal through to the speakers.
        Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

        Comment

        • JimBanville
          Senior Member
          • Aug 2020
          • 118
          • United States

          #5
          Re: Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Probl

          Originally posted by Khron
          You might be able to see a bit more in a non-mangled version of the service manual:



          There's a slide switch on the bottom-right of page 47 (containing the power amps), that goes to a signal called "8/4" going to the microcontroller, and a "/4ohm" signal coming back to the power board. That seems to drive some opto-controlled triacs(?).

          I've got a hunch those just alter the amplitude of the supply rails (lower voltage for the lower impedances, higher voltage for the higher impedances), so as to keep the required current about the same.

          I doubt flicking that switch would do much (or anything) if you weren't passing any signal through to the speakers.
          Thanks! I was listening to music as I flipped switch to see if I could hear any difference. That didn't seem unreasonable at the time. Lol. Had I heard a "pop" or anything out of the ordinary, I'm sure I would have stopped. I heard nothing when flipping the switch. The music just continued as normal. I expected "something" to change, but heard nothing.

          Comment

          • R_J
            Badcaps Legend
            • Jun 2012
            • 9535
            • Canada

            #6
            Re: Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Probl

            In this model, the switch tells the microprocessor input to change between 4/8 Ω which changes the voltage supplied to the output transistors via the circuit on page 82 (pdf 47) so switching the 4/8 switch will change the output supply voltage from around +/- 55vdc to +/- 80vdc

            Comment

            • JimBanville
              Senior Member
              • Aug 2020
              • 118
              • United States

              #7
              Re: Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Probl

              Originally posted by R_J
              In this model, the switch tells the microprocessor input to change between 4/8 Ω which changes the voltage supplied to the output transistors via the circuit on page 82 (pdf 47) so switching the 4/8 switch will change the output supply voltage from around +/- 55vdc to +/- 80vdc
              Thanks! So you think changing that voltage while powered-on would be bad for the transistors? Seems unlikely to me but you all are the experts. Haha

              Comment

              • R_J
                Badcaps Legend
                • Jun 2012
                • 9535
                • Canada

                #8
                Re: Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Probl

                Originally posted by JimBanville
                Thanks! So you think changing that voltage while powered-on would be bad for the transistors? Seems unlikely to me but you all are the experts. Haha
                Normally the impedance switch is right on the outputs and switches the actual output. but not in this case, it just increases the voltage to supply more current with the lower impedance speakers. Changing the switch in this case could damage the scr's SR121 especially if the unit was operating at a high volume.
                Keep switching it and let us know what blows up!
                Last edited by R_J; 01-25-2021, 01:01 PM.

                Comment

                • JimBanville
                  Senior Member
                  • Aug 2020
                  • 118
                  • United States

                  #9
                  Re: Switched speaker impedance selector w/ Yamaha HTR-5740 RX-V450 powered on!! Probl

                  Originally posted by R_J
                  Normally the impedance switch is right on the outputs and switches the actual output. but not in this case, it just increases the voltage to supply more current with the lower impedance speakers. Changing the switch in this case could damage the scr's SR121 especially if the unit was operating at a high volume.
                  Keep switching it and let us know what blows up!
                  Thanks for the info!!!
                  Lol. I assume you are joking about continuing to flip the switch when powered on. Why would I? I was simply curious "what" I could have potentially harmed and "why". I was also slightly hoping a knowledgeable person might look at the schematic and see no issues to the point of even "questioning" the warning in the first place. Haha. I had read about those switches in the past, but this was my first receiver with one. Nothing I ever read about them ever warned about adjusting them when powered on. Fortunately I picked this yamaha up for $6 at a goodwill type store last week, so it wouldn't have been a total disaster had I damaged something

                  Comment

                  Related Topics

                  Collapse

                  • MobileXT
                    Yamaha DXR15 Powered Speaker Fault LED On
                    by MobileXT
                    Hello Everyone! I have a Yamaha powered speaker DXR15. The problem was the RED LED Fault indicator is steady on when I power the speaker. I did open the module and I don't see any burnt component. I Downloaded the Schematic but I don't know where to start the diagnostic. Any help would be greatly appreciated. I also attached the schematic here...
                    01-17-2025, 12:43 AM
                  • sukaht
                    Yamaha MSR400 - Powered PA Speaker
                    by sukaht
                    Hello everyone.
                    I need help with my Yamaha MSR400 - Powered PA Speaker that I bought it used recently.

                    It is power on, and sounding good / working perfectly fine. However after 3 - 5 minutes, the heatsink is starting to get warm, and it smells burning a little bit.
                    I did tried multiple times on different day, event the speaker is not playing any song (input does not connect to any source, and the volume level is zero), after it turns ON, 5 minutes later, the heatsink is starting to get warm, and it smells burning a little bit. I am afraid keeping it ON longer than 5 minutes...
                    11-02-2024, 07:55 PM
                  • Phlox321
                    Yamaha EMX 2000 Powered Mixer issue
                    by Phlox321
                    Hi All

                    I have a yamaha emx 2000 powered mixer im trying to repeair.
                    the problem is that theres no sound output on the right channel. Left channel works fine.
                    Right channel has output when using the phono(headphone output) but not when going through the amplifier
                    the left peak meters work but not the right
                    the clipping light however does come on when gain is turned up same as left channel
                    What i have done so far is make sure that the supply voltages are fine, which they are
                    I found several cracked solder joints on the amplifier board which...
                    10-19-2022, 11:45 AM
                  • sanalelevenstar
                    Yamaha RX-V485 Wn9711 Update
                    by sanalelevenstar
                    Help Needed: Yamaha RX-V485 Network Issue After Firmware Update (WN9711 Error)

                    Hi everyone,

                    I'm facing an issue with my Yamaha RX-V485 receiver. During a firmware update, the process failed, and now the USB, Bluetooth, and network functionalities are not working. Occasionally, the receiver displays the error code WN9711.

                    I came across Yamaha Technical Bulletin No. 0103, which describes a similar issue for models like the RX-V4A, RX-V6A, and RX-A2A. According to the bulletin, the issue can be resolved by shorting soldering points (e.g., J260 for RX-V4A or...
                    12-04-2024, 04:32 AM
                  • jjne
                    Yamaha RX V675 sound issues
                    by jjne
                    I have an old Yamaha RX V675 receiver which is starting to develop issues with the sound, although it doesn't quite match up with what folk normally report with these.

                    From cold, the sound cuts in and out. When this happens the amp is losing sync with the optical input (speaker graphic disappears from the front panel). But this is not resolved by putting the unit into pure direct mode. After a couple of minutes this resolves, although there are occasional clicks from the speakers after that.

                    At first I thought it was either a speaker relay or the DSP, but I don't think...
                    06-24-2025, 07:01 AM
                  • Loading...
                  • No more items.
                  Working...