Technics SU-VX800 amplifier

Discussion in 'Technical Repair' started by Marius83, Dec 28, 2017.

  1. Marius83

    Thread Starter Member

    Dec 28, 2017
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    Okey guys, so either one of those two will do the job, if only amount is the difference, thanks.
    I just got my oscilloscope up and running... :)
    Of course i can just order the rectifier, but it could be fun to check it at first with my oscilloscope, if it's good enough to do the job.. :rolleyes:

    How do i measure the main power rails with it?



    [​IMG]
     
  2. JoeJester

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    Apr 26, 2005
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    Is there a link to the manual for your oscope so we can have an idea of what you are working with?
     
  3. Marius83

    Thread Starter Member

    Dec 28, 2017
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  4. MrChips

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    Oct 2, 2009
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    To measure power supply ripple with your DSO138 scope, set:

    SW1 - AC
    SW2 - 1V
    SW3 - x1

    SW4 - Running

    Press SW7 until the desired feature is selected which will be hilighted. Use SW5/SW6 to change highlighted setting.

    Set time sweep to 5mS
    AUTO

    (if you set to NORM, press SW7 until arrow on right edge of screen changes from purple to blue. Then use SW5/SW6 to move arrow UP/DOWN while watching the trigger voltage setting at the top right of the screen).

    Show us a photo if you can.

    You can HOLD the scan by pressing SW4.
     
  5. JoeJester

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    Apr 26, 2005
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    @Marius83 It's good to know what your equipment can do. We know you can only view up to 40V peak to peak, so we won't ask you to measure some signals as most from stage 3xx to the output audio can exceed 60 V peak-to-peak. Now if you manage to get a x10 probe, then those measurements could be safely made.
     
  6. Marius83

    Thread Starter Member

    Dec 28, 2017
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    Okey.
    Will these be the correct ones?
    Only problem is it takes three weeks for them to show up..

    https://www.ebay.com/itm/P6100-2pcs...697257&hash=item466de5d468:g:ot0AAOSwonBZ5gIC
     
  7. JoeJester

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    I just noticed you were in Norway. Yes, that style would work.
     
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  8. Marius83

    Thread Starter Member

    Dec 28, 2017
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    Yes I am located in Norway.:)
    What about it?

    The shipping takes so much time just because all these items from China are included some free shipping...
    But i just found the same item with another shipping option, i might get it a lot quicker !
     
  9. JoeJester

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    Nothing wrong with Norway. I am ignorant with respect to the supply chain over there.
     
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  10. Marius83

    Thread Starter Member

    Dec 28, 2017
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    Set up the way you said on the picture.
    I have ordered an x10 probe like JoeJester suggested, when it arrive we can measure i guess :)

    [​IMG]
     
  11. MrChips

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    Oct 2, 2009
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    Have you tried using the DSO138 to take any measurements as yet?

    Connect the BNC cable with the alligator clips to the input BNC jack.
    Touch the RED alligator clip with your fingers. You should be able to pick up 50Hz line frequency.

    Play with the SEL control (SW7). This allows you to cycle through the following options:

    HORIZONTAL POSITION
    VERTICAL POSITION
    TIME/DIV
    MODE - Single / Normal / Auto
    TRIGGER SLOPE
    TRIGGER LEVEL

    Use the UP/DOWN buttons to alter the selected option

    DSO138.jpg


    In order to get a periodic waveform to stay stationery on the screen, adjust either VERT POSITION or TRIGGER LEVEL such that the TRIGGER LEVEL is positioned between the minimum and maximum portions of the trace.

    The green "Triggered" LED at the bottom of the board should be flashing when the scope is being triggered.
     
  12. MrChips

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    Oct 2, 2009
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    Your DSO138 shown in the photograph is displaying a +0.5V offset when no signal is present.

    To correct this:

    Set CPL (SW1) to GND
    Press SEL (SW7) until the VERTICAL POSITION arrow is highlighted.
    Press and hold [OK] HOLD/RUN (SW5) for 2 seconds. This will shift the trace down.
    Adjust the VERTICAL POSITION to bring the arrow back to the centre line.
     
  13. Marius83

    Thread Starter Member

    Dec 28, 2017
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    Thank you MrChips for the guide to use my oscilloscope, i have scrolled through options and have got more familiar with it.

    I have corrected what you said, and here's a picture what it picks up when i hold the RED alligator clip with my finger.



    [​IMG]
     
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  14. MrChips

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    Oct 2, 2009
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    Nice.

    Now, as an exercise, see if you can calculate the line frequency from the information of the scope.
     
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  15. Marius83

    Thread Starter Member

    Dec 28, 2017
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    Okey i'll try :)
    I guess since it set to 5ms, one grid division would be 5ms, a complete cycle of the signal is 4 divisions, so if i convert 20ms it would be 50hz

    I just don't understand how it picks up 50 hz from my finger...?
    I did google it.. -so i am actually an antenna, amplifying the frequenzy of my electricity in the house... in this case my garage.. hehe.
     
  16. JoeJester

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    Apr 26, 2005
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    Your body is a good receiving antenna. Think about how you can "perceive" 1 mA of current, and 100 mA can kill you. You have body resistance. You can measure it. And if you wet your fingers and remeasure, the resistance will be lower.
     
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