KA7808 Voltage Regulator

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  • dj_ricoh
    Badcaps Legend
    • Jan 2013
    • 2073
    • uk

    #1

    KA7808 Voltage Regulator

    hy guys

    still learning, so stupid Q incoming

    i got this crap *&&%&* cd player i wanna fix(won`t power) and PSu i think its ok.

    i just try to find thinks that i don`t know and i wanna know how it works.

    So, i put this regulator on the PSU and see how it outputs

    everything its ok until i pass 8V, i get stuck on 7.85V



    ups sry for the side pics
    Attached Files
    Last edited by dj_ricoh; 01-04-2014, 08:38 AM.
    Just cook it! It's already broken.
  • tom66
    EVs Rule
    • Apr 2011
    • 32560
    • UK

    #2
    Re: KA7808 Voltage Regulator

    That would appear to be working, it is an 8V device.
    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

    • dj_ricoh
      Badcaps Legend
      • Jan 2013
      • 2073
      • uk

      #3
      Re: KA7808 Voltage Regulator

      ty tom

      Back to testing crap caps
      Just cook it! It's already broken.

      Comment

      • tom66
        EVs Rule
        • Apr 2011
        • 32560
        • UK

        #4
        Re: KA7808 Voltage Regulator

        Crap caps would be unexpected, and would probably only cause poor audio quality, digital skipping, etc. Does CD player have a track number display? If so, focus on the controller chip for that (probably surface mount, bottom of board) -- if you can find a datasheet for it, check the VDD etc supply voltages.
        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

        • mariushm
          Badcaps Legend
          • May 2011
          • 3799

          #5
          Re: KA7808 Voltage Regulator

          The 7808 is a linear regulator.
          Like any linear regulator, it has a specific voltage drop. In the 78xx family this voltage drop is 2v, but it can be slightly less if there's nothing connected at the output or something that uses very little power (like a led for example).

          So if you want to make sure it works fine and outputs 8v, you need to give an input voltage of at least 10v. If you give it less than 10v, it will output Vin - ~ 2v.

          So you got 7.85v - this is a bit outside the tolerance, a bit far away from 8v. But, I don't know what input voltage you used. Ah nevermind, I see 15.4v on the power supply. It's a bit low to see 7.85v but I wouldn't consider the regulator bad right away.

          Comment

          • tom66
            EVs Rule
            • Apr 2011
            • 32560
            • UK

            #6
            Re: KA7808 Voltage Regulator

            7.85V is within 2%, regulator like that is typically 5% tolerance.
            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

            • PeteS in CA
              Badcaps Legend
              • Aug 2005
              • 3576
              • USA, Unsure of Planet

              #7
              Re: KA7808 Voltage Regulator

              One convenient thing about the part numbering of uA78xx and uA79xx type parts (and LM340-xx and LM320-xx parts) is that the "xx" is the output voltage. How +8V and -8V came to be standard voltages (and for what), I don't know.
              PeteS in CA

              Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
              ****************************
              To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
              ****************************

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