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Yamaha RX-V450 -- Dead

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    Yamaha RX-V450 -- Dead

    £20 on eBay for this nice 6.1 channel Yamaha amplifier. Rated at 0.02% THD+N at 100W output; 350W maximum output power across all channels. Despite the ".1", it doesn't actually have a built in subwoofer amplifier. It does have a line-level sub output. It also uses one less far-rear speaker, so it's only got 6 surround channels.

    After I saw Dave Jones' (EEVblog) video on this amp, I had a look around eBay and saw there was a plentiful supply of this amplifier or its cousins going faulty on eBay. Picked one up for £20, plus another £10 got three half-decent speakers plus a subwoofer+amp (Combined unit; I'll post pictures of it in another thread.)

    The fault is that the amplifier is completely dead or will only power up intermittently. And the cause? A single poly capacitor worth about £0.50. I just blasted this cap with a little freeze spray and it fired right up complete with functioning sound on the FM tuner.

    This amplifier uses a rather novel, but somewhat complex energy saving standby circuit. It uses a real mains transformer, but switches it on and off a few times a second depending on load -- a sort of proto-switching power supply. It manages 0.2W standby power by doing that, whilst satisfying audiophiles (because it doesn't use a real switching power supply.)

    The poly capacitor supplies the power to a D-type flip flop which latches the transformer on for a few cycles about three times a second using a FET and bridge rectifier. It also powers an optocoupler which tells the CPU if the AC line is present. When the poly cap falls in capacitance (typical failure mode due to self-healing from mains spikes), the voltage across the optocoupler drops, the signal goes away, and the CPU switches off the amp completely (no sign of life at all -- no standby light, no clicks from the relay...)

    Now, this amplifier basically only fails in 230V markets. It's perfectly reliable when used on 115V (if it is rated for 115V of course.) Try and think why it might matter...

    It's a Christmas present for my dad to accompany the 50" plasma (also one I repaired.)
    Attached Files
    Last edited by tom66; 11-17-2012, 06:11 PM.
    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

    #2
    Re: Yamaha RX-V450 -- Dead

    My error. It's C405; the red cap near the top of the PSU, not that large green one.
    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

    Comment


      #3
      Re: Yamaha RX-V450 -- Dead

      It's fixed now. I bodged a much larger WIMA capacitor in...

      The original, failed cap read 6.5nF instead of 22nF.
      Attached Files
      Last edited by tom66; 11-18-2012, 09:54 AM.
      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

      Comment


        #4
        Re: Yamaha RX-V450 -- Dead

        Very weird standby supply circuit.

        If this was just a plain old transformer, then hundreds of these units would still be in operation...
        Muh-soggy-knee

        Comment


          #5
          Re: Yamaha RX-V450 -- Dead

          Yeah, but simple transformers have been banned by the EU, because they use too much in standby. Silly law, probably causes more waste than it stopped... but it looks good from a political standpoint.
          Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
          For service manual, schematic, boardview (board view), datasheet, cad - use our search.

          Comment


            #6
            Re: Yamaha RX-V450 -- Dead

            Originally posted by tom66 View Post
            Yeah, but simple transformers have been banned by the EU, because they use too much in standby. Silly law, probably causes more waste than it stopped... but it looks good from a political standpoint.
            I sure didn't know about that!!!

            //begin rant

            What a lame law... iron core transformers are usually capable of >95% efficiency!

            Instead, they should ban CFL's and their spike making, energy-meter fooling madness!!!

            //end rant
            Muh-soggy-knee

            Comment


              #7
              Re: Yamaha RX-V450 -- Dead

              Transformers are really efficient -- but only when loaded significantly. When unloaded, they are essentially drawing a couple of watts continously. Look up magnetising current. Iron-core transformers are banned except for AC-AC supplies (which are in continuous use) i.e. wall warts. Due to the ban on AC-DC supplies, the price of AC-AC supplies has increased significantly making them less cost effective. You are still allowed to use a transformer in your audio amplifier, but the standby power must be less than 1W unless it offers some kind of timer or recording feature, in which case the limit is a generous 2W.

              CFLs are fine, but the current cost cutting annoys me, because they sure don't last 15,000 hours like they claim. Usually the main primary electrolytic cap fails. It should be possible to design a lamp which doesn't use one of those. I designed a self-oscillating current-controlled LED power supply which uses NO electrolytic caps; the output flickers at 100Hz, but so do filament bulbs, so no-one notices. It's also got 0.9 PF and short circuit/open circuit protection.
              Attached Files
              Last edited by tom66; 11-18-2012, 04:08 PM.
              Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
              For service manual, schematic, boardview (board view), datasheet, cad - use our search.

              Comment


                #8
                Re: Yamaha RX-V450 -- Dead

                Forgot to include the diagnosis video and to say it's fixed now.
                https://www.youtube.com/watch?v=efRnYAcT7us
                Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                Comment


                  #9
                  Re: Yamaha RX-V450 -- Dead

                  Great work and a good price for such a meaty looking amp!!

                  /Not sure about the Jamcon 1uf start cap though

                  Chris...

                  Comment


                    #10
                    Re: Yamaha RX-V450 -- Dead

                    Everything else is good caps. Jamicon seem to be fine for general purpose, though I admit it's probably saving less than a cent and the rest are quality caps, it seems strange.
                    Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                    For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                    Comment


                      #11
                      Re: Yamaha RX-V450 -- Dead

                      A local repair guy told me that even mains rated capacitors used to replace the 22nf eventually fail also. I dont know the brand of capacitor, only that it is 275VAC.

                      Comment


                        #12
                        Re: Yamaha RX-V450 -- Dead

                        I used a 1250V rated cap, I think it will be OK.
                        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                        Comment


                          #13
                          Re: Yamaha RX-V450 -- Dead

                          Yeah, I was really happy with the amplifier, but i fear its a dead cap in mine too. I know my way around soldering, but how to see if it really is this capacitor? Freeze spray is unknown to me.

                          Comment


                            #14
                            Re: Yamaha RX-V450 -- Dead

                            have you got any air duster the type used to clean pcs etc if so you can turn the can upside down and use that as freeze spray it does work and is a lot cheaper to buy imo.

                            Comment


                              #15
                              Thanks for this info, my brother came with this amp, totally dead. Just replace the cap and it works again.

                              Comment

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