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Satellite receiver Power supply higher voltages output

Discussion in 'Troubleshooting and Repair' started by pharaon, Apr 20, 2020.

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  1. pharaon

    pharaon

    373
    6
    Oct 28, 2014
    This power supply output voltages is higher than it should be, what could be the cause
    Standard voltage actual voltage
    23V = 32V
    12V = 18.5V
    3V = 7 V
    Next 3V = unstable 0.5 to 1.6 V
    5 V = unstable 6.8V to 7V

    [​IMG]
    [​IMG]
    [​IMG]
     
  2. Bluejets

    Bluejets

    4,492
    957
    Oct 5, 2014
    How are you measuring those readings..?
     
  3. pharaon

    pharaon

    373
    6
    Oct 28, 2014
    that way, if that's what you mean
    [​IMG]
     
  4. Cirkit

    Cirkit

    132
    10
    Oct 28, 2015
    Try measuring those voltages again with your black probe on the respective GND pins.
     
  5. Bluejets

    Bluejets

    4,492
    957
    Oct 5, 2014
    Perhaps but it might be different if you use the black probe on the reference "GND" that is adjacent to each 3v3, 5v and 12v etc.
    23v is the far right, not the second as you have marked.

    Which meter range are you using?

    Edit...Cirkit...beat me by .......that much) :)
     
    Cirkit likes this.
  6. pharaon

    pharaon

    373
    6
    Oct 28, 2014
    Done it and same results

    same results as well
     
  7. Bluejets

    Bluejets

    4,492
    957
    Oct 5, 2014
    Meter on dc range..?
    Meter tests ok..?
    unusual for any reading to go higher than normal (within tolerances)
    Input voltage/frequency match input requirements..?
    Board looks to have been pretty warm around the switcher ic and associated bits.
     
    Last edited: Apr 21, 2020
  8. pharaon

    pharaon

    373
    6
    Oct 28, 2014
    yes

    yes

    yes

    although it's working and there's an output voltage

    i need to know the cause of the higher output voltage, cause it cause the receiver to hang up while working or give me "searching for signal" for some channels
     
  9. Bluejets

    Bluejets

    4,492
    957
    Oct 5, 2014
    Yes I did realise that. :)

    I guess so but not the right values so something is amiss.

    Still seems rather strange to have much higher indicated voltage levels.

    Could be a fault somewhere in the feedback section.
     
    duke37 likes this.
  10. pharaon

    pharaon

    373
    6
    Oct 28, 2014
    So what to check?
     
  11. Cirkit

    Cirkit

    132
    10
    Oct 28, 2015
    What voltage do you measure at IC1? Does the capacitor next to it have a domed top - hard to tell from the photo angle?

    Have you tested all the output diodes?
     
  12. pharaon

    pharaon

    373
    6
    Oct 28, 2014
    no

    at what pic exactly should i do the measurement
     
  13. Bluejets

    Bluejets

    4,492
    957
    Oct 5, 2014
    Look for details on the switcher (5L0365R) which should bring up a data sheet and a load of schematics.
    Perhaps not exactly the same as your board but enough to get an idea of the layout.
    I found a couple of videos but mostly Russian/Vietnamese so not much help but it does show it is a fairly common type of board.



     
    Last edited: Apr 21, 2020
  14. Cirkit

    Cirkit

    132
    10
    Oct 28, 2015
    If IC1 is a KA431 or similar, look at the values of the two resistors closest to it. You should be able to work out the set voltage.
     
  15. pharaon

    pharaon

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    Oct 28, 2014
    how to tell if it's?

    can you explain to me how can i?
     
  16. Cirkit

    Cirkit

    132
    10
    Oct 28, 2015
    Can you read the markings off the flat side of the component?

    You will need to trace the resistors that form a potential divider for that IC. Watch the video above, you are looking for the equivalent to R204 and R205 connected in the same way to IC1 on your board.
     
  17. pharaon

    pharaon

    373
    6
    Oct 28, 2014
    [​IMG]
     
  18. Cirkit

    Cirkit

    132
    10
    Oct 28, 2015
    Not the controller IC. The small 3-pin component marked IC1 next to it.
     
  19. pharaon

    pharaon

    373
    6
    Oct 28, 2014
    [​IMG]

    i also have tested the big cap 47uf 400V and it gave me 36uf, is that acceptable? and can it cause such higher voltage in the output ?
     
    Last edited: Apr 22, 2020
  20. Cirkit

    Cirkit

    132
    10
    Oct 28, 2015
    Now find the two resistors that form the potential divider for that part.

    How did you measure the capacitor? Was it discharged first, in-circuit?
     
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