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Vizio s3851w-d4 power supply schematics

Discussion in 'Datasheets, Manuals and Component Identification' started by vizioUsr, Jan 23, 2018.

  1. vizioUsr

    vizioUsr

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    Jan 23, 2018
    HI,

    I am a newbie here and I am trying to repair my Vizio s3851w-d4 soundbar.
    The problem with it is that it is not powering on.

    The power board normally takes 110V AC input and provides 24V and 5V dual output. However this board is only providing the 5V output and not the 24V output.

    I have narrowed it down to the step down transformer. (see the image, it is the transformer with the markings MK BCK32BK)
    Where can I get the schematics of the power supply board to get the details about the transformer?
    The model number on the board is 0500-0515-2180.
     

    Attached Files:

  2. kellys_eye

    kellys_eye

    4,284
    1,145
    Jun 25, 2010
    It's more likely to be the capacitor to the right of this transformer that needs changing:

    part.png

    Looks suspiciously 'bulging' to me - a common cause of faults like yours. There may by other dud parts but the capacitor needs changing anyway. Post close up image of this area, top and bottom of board.
     
  3. dave9

    dave9

    768
    171
    Mar 5, 2017
    So you're stating that you measured power (voltage) coming into the transformer, across the primary coil, but measure none on the 24V output coil? If so, I don't think that will be an easy transformer to find (I could be wrong because internet, lol). It would probably be easier to find a whole Vizio power board.

    However in my experience the transformer itself is not nearly as likely to fail as the switching transistor(s) right before it under that finned heatsink, or the diode(s) after it under the flat plate heatsink, or of course any bulging capacitors as Kellys_eye mentioned... I just can't tell if the one pictured is bulging or it's just the way the light is reflecting off of it.

    I see at least 8 pins on the output connector. What's going on there? Are several in parallel to supply more 24V power, all pins are either power rails or ground, or is there logic triggering the 24V on while the 5V is always on for sensing purposes?
     
  4. vizioUsr

    vizioUsr

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    Jan 23, 2018
    There are five pins on the left side (input) and four pins on the right side of the big transformer.
    The middle pin on the left is not connected to the board. I see two wires from within the transformers connecting there.
    In the board there are four slots on the left and four on the right for the transformer.

    I did the continuity test with the multimeter (forgive me if I say something wrong, I am a newbie with electronics) on both ends of the big transformer. On the input side (left) the first two at bottom and the two at the top were continuous (there was a beep from the multimeter). However there was no beep when I checked any one from left side bottom two pins and any one from the left side top two.

    When I did the same on the output side (right side), I was getting a beep for whichever combination of pins I selected.
     

    Attached Files:

  5. vizioUsr

    vizioUsr

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    Jan 23, 2018
    I tried searching for the power board but couldnt find it anywhere.
    Its model number is 0500-0515-2180.
     
  6. Bluejets

    Bluejets

    3,453
    698
    Oct 5, 2014
    As others have said, forget the transformer.
    Continuity test will not prove anything as the windings are generally only a few turns of fine wire.(maybe 30swg)
    Not a common thing to burn out windings.

    Even if it was, it would be quite obvious physically.
    Perhaps do some research into switch mode power supplies and see what the windings in other systems do.
    Yours will most likely be similar in many ways as far as operation.
    May help to diagnose the fault.
     
  7. kellys_eye

    kellys_eye

    4,284
    1,145
    Jun 25, 2010
    Change C21 - definitely broken.

    As stated, probably nothing wrong with the transformer - just your technique for measuring it!
     
    Bluejets likes this.
  8. vizioUsr

    vizioUsr

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    Jan 23, 2018
    C21 is linked to the smaller transformer which provides 5V. It is working fine as I am getting the 5V at the end.
     
  9. kellys_eye

    kellys_eye

    4,284
    1,145
    Jun 25, 2010
    Change it anyway - or show a close-up picture of it. The top definitely looks domed to me, possibly split, and it WILL cause problems either now or later.

    The output of the 24V may require 'something' from the 5V supply - and if it isn't 'smooth' (this is what the capacitor does) then it may cause a problem/loss of the 24V output. Indeed if the 5V is supplying a logic section then it is usually required to be 'fired up' BEFORE the 24V is allowed to be switched on so if there is anything stopping the 24V from working it may just be a dodgy 5V supply.
     
  10. vizioUsr

    vizioUsr

    8
    0
    Jan 23, 2018
    I have attached the closeup image of the capacitor.
    If you look at the other image, the place where it is written HOT is directly below the large transformer which provides 24V and the 4 pins below the place where it is written COLD is the output of that transformer.

    The area marked in red is where the output of the 5V transformer comes.
     

    Attached Files:

    • C21.jpg
      C21.jpg
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    • Board.jpg
      Board.jpg
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  11. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Well the clear pictures don't show the 'bulge' as the earlier pics did so forget this issue.

    Can we have more clear images of the 'hot' end of the board (both sides)? We'll try to pint out where to take some appropriate measurements to localise the fault.
     
  12. dave9

    dave9

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    Mar 5, 2017
    Now that I see the back of the board, it looks like there is a "STBY" (Stand by?) pin which may need a signal for 24V to be supplied.
     
  13. vizioUsr

    vizioUsr

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    Jan 23, 2018
    I have attached the clearer pic of both the front side and back side of the HOT end of the board.
    Yesterday, in a moment of rash decision, I ripped out the 24v transformer. :( Now I feel totally bad about it. I need to find a replacement transformer.

    I had another plan going on... I was thinking of replacing the entire board with a 110VAC to 24V 4A adapter and use a DC-DC converter to convert it to 5V 3A and use it to supply the required 24V, 5V and GND to the end.
    I am unsure about the STBY pin.

    I had these products in mind
    Adapter
    DC-DC Converter
     

    Attached Files:

  14. dave9

    dave9

    768
    171
    Mar 5, 2017
    If the amp board isn't coming out of standby and sending a signal to turn on 24V, even with 24V from an alternate PSU it might not work. It could be that there was nothing wrong with the amp board (including transformer), that it just wasn't getting the power-on signal from a faulty amp board.

    On the other hand there could be less smarts to it and if you supply 24V from a different PSU, it's always on, powering the amp and usable, which could waste a bit of power but hopefully not produce a perpetual buzzing sound when the source (TV?) is off or muted.

    Do you have an alternate source of DC power for testing before you buy something? It probably don't need to be 24V, just for testing you could wire up a 12VDC/1A wall wart. Odds are that's enough to see if the amp board works even if it runs out of current or voltage and starts distorting at higher volumes.

    Well I take that back, it depends on how the board is set up. If it has opamps before the power amplification stage and they're on power rails with linear regulators set to a voltage higher than 12V + Vf overhead of the regulator then you'd need an input voltage at least that high, but it wouldn't hurt to try (12V or whatever, 12V seems like a minimum voltage worth trying since 12V wall wart AC/DC supplies are quite common, practically everyone has some already, or a 12V car/etc battery, laptop AC/DC power brick, whatever.

    Anyway, if you end up buying a 24V PSU, I don't see a need to regulate down the 5V from that when your original board seems to still do 5V, or was there 5VSB on the small transformer but the main 5V rail was on the transformer you ripped out?

    If the old board provides all the 5V power needed still, just wire the 24V to it and let it supply 5V.

    The 24V adapter you linked to on Amazon is probably a cheap design with dirty (high ripple) output and short lived. It is possible you could improve it by cracking it open (as non-destructively as possible), swapping in better, slightly larger capacitance major brand low ESR capacitor(s) and drilling some vent holes in the casing, small enough to not be an electrical hazard.

    Even so the easier route would be choose a major brand 24V PSU instead, or if on a tight budget, accept a little lower peak amp power by choosing a high end (gaming, etc) laptop AC/DC power brick that is a little lower DC voltage, I mean the OEM major brand adapter for it instead of a generic aftermarket adapter.

    Good pictures of the front and back of the amp board might help... or they might not, hard to say but that might help determine if there are things like the linear regulator(s) for opamps as mentioned above, unless they used tiny TO92 package or small package surface mount regulators that we can't ID from a top down picture.

    Once you get power to the amp board and see what you're dealing with, such things like input power to opamps, if present, can be measured with a multimeter.
     
    Last edited: Jan 24, 2018
  15. vizioUsr

    vizioUsr

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    Jan 23, 2018
    I finally had to ditch the OEM power supply board.
    I went ahead with Plan B and used a 24V PSU and a DC-DC converter. I was on a tight budget, so I went ahead with purchasing the same one I mentioned in my previous post.

    The ouput was a ten pin connecter which matched the same output of the OEM PSU - 3 24V pins, 4 GND, 2 5V pins and the last pin was left with no connection (STNDBY). I was not sure whether to provide any input to that pin.

    Soldered the connections in place and voila! It works!

    Yeah there is a small buzzing sound, but only at high volumes when the tv is switched off. However, on pressing the power button in the soundbar remote, the buzzing sound will no longer be there.
    The buzzing is not much of an issue, as when the tv switches off, the soundbar is switched off too. So not much of a problem.

    I wish to thank everyone who provided their valuable suggestion in helping an amateur like me understand the problem.
     
  16. hauns

    hauns

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    Jun 12, 2018
    ok, another newbie here - with exactly the same problem: 5v ok, 24v down on that power board. no white light in front when trying to power on.

    can you pls post a pic of you final solution? you basically used an external power supply (24v) and a converter to 5v? did you keep the original board so you can use the same connector? does the remote work as before? does the power button on the unit work as before?

    thanks for the add'l details. obviously, if - in the meantime - you were able locate the actual pb of the defective board/new insights - that would be appreciated as well!
     
  17. vizioUsr

    vizioUsr

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    Jan 23, 2018
    I ditched the original power supply board.
    Yes the remote works the same as before. Power button and all other functions work as expected.

    I could not find any replacement boards. Since it was working fine I didn't look further.
     
  18. rjmcfadd

    rjmcfadd

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    Jun 12, 2018
    This is really weird, my sound bar just stopped working this past weekend. I took it apart and found that it had the same problem as yours. I found that if I soldered a connection between the 5V and the standby pin on the output, the 24V will appear. I haven't tested this in my soundbar yet but it should do the trick.

    [​IMG]
     
    Last edited: Jun 12, 2018
  19. hauns

    hauns

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    Jun 12, 2018
    hmm this may actually make sense: a knowledgeable lad (or lass?) over at https://www.reddit.com/r/AskElectro...vizio_soundbar_possible_power_supply/dv3lxdh/ explains that the 24v circuit only comes by demand (to save power) - a pulse via the standby pin? so this board (5v always on, 24 by default off) may actually not be broken, only the input from the power button/remote may be faulty.

    your solution of supplying always 5v power to the standby makes sense. maybe a step further could be to attach some wires and make a simple toggle switch?
     
  20. Kokewafa

    Kokewafa

    1
    0
    Jul 4, 2018
    Hello i just got the samw issus can you provide the links for that 24v psu and DC-DC convertor please i wanna buy then
     
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