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Am i testing it right

Discussion in 'General Electronics Discussion' started by philipshadow, Jul 4, 2021.

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  1. philipshadow

    philipshadow

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    Oct 29, 2020
    I want to know what will make the switch of B1 and B2 to close so that current can pass thru.
     

    Attached Files:

  2. philipshadow

    philipshadow

    36
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    Oct 29, 2020
    I have a microwave that is faulty and i am testing the voltages of the individual major components. When you look at the lamp the voltage at both terminals read 250v Ac on the multimeter. I am using the AC(Neutral) from the main power board as reference voltage for 0v. Likewise the same 250v Ac on both terminals for this big transformer and the fan motor. can anyone confirm if the readings i am getting are okay or not okay.
    The link below is for the power board.
    https://pasteboard.co/K9D8S8N.jpg
     

    Attached Files:

    Last edited: Jul 4, 2021
  3. Cirkit

    Cirkit

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    Oct 28, 2015
    It seems that the switch is closed when the door to the equipment is closed. It's odd that the positive output of the power supply is connected to the chassis?
     
  4. philipshadow

    philipshadow

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    Oct 29, 2020
    ohkay
     
  5. Minder

    Minder

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    Apr 24, 2015
    Also very strange the neutral is being switched rather than the Live.?
     
  6. crutschow

    crutschow

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    May 7, 2021
    You need to measure the voltage across the lamp terminals and across the transformer terminals, that's the voltage that does the work, not necessarily the voltage to neutral.
     
  7. Bluejets

    Bluejets

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    Oct 5, 2014
    if they're measuring mains, there really is no option on a single phase supply

    Op, when you measure each side of a particular load with reference to neutral and you get 250v on both sides, it simply means there is a circuit through the part but no neutral to complete the circuit..
     
    Last edited: Jul 5, 2021
  8. crutschow

    crutschow

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    May 7, 2021
    Read again what I said.
     
  9. philipshadow

    philipshadow

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    Oct 29, 2020
    i did that but i didnt get any reading, just 0v. That is when i now decided to measure each side with respect to ground and i was getting readings
    so does it mean if i find the circuit without neutral and close that circuit 250v will only be on one part of the components that require 250v.
     
    Last edited by a moderator: Jul 6, 2021
  10. philipshadow

    philipshadow

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    Oct 29, 2020
    hmmmm. It a microwave from sony i am trying to repair
     
  11. Martaine2005

    Martaine2005

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    May 12, 2015
    Are you sure you should be playing with 240 volts? It doesn't seem like you should from your questions.
    Have you checked the door switches with the oven unplugged and door closed and open?

    Martin
     
    davenn and Harald Kapp like this.
  12. Bluejets

    Bluejets

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    Oct 5, 2014
    I read it right first time and my answer still applies.
     
  13. philipshadow

    philipshadow

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    Oct 29, 2020
    Yes, i have checked the switches and the door relays. i have a similar schematics but one of the board is missing from it but all others are the same. All are good according to my test using the schematics as baseline for my measurement.
     
  14. Martaine2005

    Martaine2005

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    May 12, 2015
    I have not read what the actual fault is.

    Martin
     
  15. philipshadow

    philipshadow

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    Oct 29, 2020
    The issue is no display. The lamps in my house and other houses were flickering one night and i was awake by then. suddenly i saw a spark at the microwave. By then it was on standby. after the spark the standby display which was a timer that flashes was no more appearing. I opened the microwave and found the varistor in the control board dead had cracked and dark spot underneath the control board. i changed the varistor but still no display.i have checked all other components and they check out good. however there is a transformer on the power board that is not producing any secondary voltage but i dont know how many voltages that transformer has to produce. i have posted it in another thread titled
    Help identifying output voltages
     
  16. Martaine2005

    Martaine2005

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    May 12, 2015
    You have lots of different threads. Very confusing.
    The schematic shows a 25V filter cap after the bridge rectifier suggesting the secondary to be low voltage. Probably between 10V and 16V.

    Martin
     
  17. philipshadow

    philipshadow

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    Oct 29, 2020
    ohkay does it mean this transformer only produces one voltage. About the other threads i wanted to delete the others but i dont know how to
     
  18. Martaine2005

    Martaine2005

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    May 12, 2015
    Not at all, it may have several. The schematic you provided for T1 has only one output.
    Here for example is a multi-tap:
    [​IMG]
    Martin
     
  19. philipshadow

    philipshadow

    36
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    Oct 29, 2020
  20. crutschow

    crutschow

    359
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    May 7, 2021
    Then you seem to have not understood what I said.
     
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