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Peavey xr684f mixer amp

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  • #1

    Peavey xr684f mixer amp

    Hi folks,

    You guys were a great help with a fault on a Marshall AVT head I was having trouble with last year, so I'm back again to tap into your knowledge.

    I've got a peavey xr684 mixer amp that won't power up. Power LED flashes momentarily when the power switch is engaged. No signs or smells of anything charred inside. I've checked the rectifier circuit and power caps. All seems ok. Anyone got any wisdom they are willing to part with on this one?

    Thanks
    JT...
    Tags: None
  • #2
    "Checked" and "seemed OK" are not very specific. What we would want to know is this - are ALL the power supply voltages present and more or less at the proper voltage? If not, what is missing?
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      XR684 preamp.pdf400SC 99.pdf

      Please see A2 on the power supply schematic 17013

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      • #4
        Yeah, sorry for being so vague. I'd only checked some of the supply components for continuity & should have been more thorough from the start. It would appear there is only a -15.4v on the ribbon cable to the preamp. The +ve volts are missing. Soundguruman thanks for the power supply schematic! I only had the preamp diagram to work from up until now. I've spent some more time with the multimeter on and it would seem that diode CR226 is shorted and is located on the positive side of the supply. Could that be the culprit?

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        • #5
          You gotta shorted zeener? That could be it, but take it out and test it to be sure.

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          • #6
            Ok, so at last I've got back to this beastie. I took the diode CR226 out of circuit to test & it's fine.

            Also at the I'm getting 25 volts on diodes CR225 & CR229.

            So, I then checked pin 3 of Q215. I am getting the same reading here as I did on the +16v pin(5) of the ribbon cable. It kind of fluctuates between .8v-9.0v constantly. It seems this is a JRC 7815A power IC. It also looks like they are no longer in production. I had a look for alternatives and a search came up with an MC7815ACTG power IC. Think I'm on the right track at last. Anyone confirm my thoughts

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            • #7
              Originally posted by thebunker View Post
              Ok, so at last I've got back to this beastie. I took the diode CR226 out of circuit to test & it's fine.

              Also at the I'm getting 25 volts on diodes CR225 & CR229.

              So, I then checked pin 3 of Q215. I am getting the same reading here as I did on the +16v pin(5) of the ribbon cable. It kind of fluctuates between .8v-9.0v constantly. It seems this is a JRC 7815A power IC. It also looks like they are no longer in production. I had a look for alternatives and a search came up with an MC7815ACTG power IC. Think I'm on the right track at last. Anyone confirm my thoughts
              LM 7815 etc... is very easy to buy. or any 7815 with a TO220 case...positive voltage regulator

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              • #8
                Great! Thanks for all the help soundguruman you're a gent!

                Ordered some & they should arrive the start of next week. I'll let you know how we go

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                • #9
                  IC arrived today, just soldered it in place, powered up & we're back in business.

                  Thanks again for the help enzo and soundguruman. You guys are legends!

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