LCD TV Power Circuit...need help please?

Discussion in 'The Projects Forum' started by NOMFET, May 26, 2010.

  1. NOMFET

    Thread Starter New Member

    May 26, 2010
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    Ok. So I've got a power supply board for some 37" Vizio TV, that supposedly won't power on. Now, I've located a fuse (T4AH250V) that is reading as no signal through the fuse. I wanted just to test it out, but all my other fuses here at the house are like T3.15AL250V or 10-15 amp fuses. How specific are fuses? I'm self taught with electronics, and can do a decent amount of troubleshooting on circuitry.

    I know I don't want to have a jumper wire in place (as it may damage the cap's on the other side) or use the higher amp fuses. Any suggestions?

    Thanks
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Use only the proper rated fuse for the device.

    As you correctly decided to not do, never jumper across a fuse.

    If the fuse blew, it could be a couple of things:
    1) There was a transient spike on the mains supply which caused it to blow.
    2) There is a fault in the circuit.

    In the case of 1) above, replacing the fuse with the same part number may restore the circuit to normal operation.

    In the case of 2) above, replacing the fuse with the same part number will result in another blown fuse, which will protect the still-good parts of the circuit.

    Never, ever, EVER use a fuse that is not appropriately rated for the device in question. To do so invites disaster. I am not kidding.
     
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  3. NOMFET

    Thread Starter New Member

    May 26, 2010
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    Roger that! Ok, so looking at the fuse I see "Buss" along with a bunch of logos (Bussman, although can't locate it on their site); and "T4A H 250V". It's tube shaped, and I would say its glass, but its milky colored. It also has a blue stripe in the very center, all the way around.

    There's a similar fuse on the board, "T6.3A H 250V", the only visable difference is that it has a red stripe instead of blue.

    I can't find these dang things anywhere. How specific of a fuse do I need for replacement? Amp/volt/type/burn speed?

    Edit:
    If it helps any the path follows as:
    AC in -> 6.3a fuse -> AC>DC -> DC(-) -> buffer caps (450v100uf) -> 4a fuse ->...

    Thanks
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    4Amp 250V rated ceramic fuse.. Should be available at your local hardware/electronics store.
     
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  5. NOMFET

    Thread Starter New Member

    May 26, 2010
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    Ceramic....Nice. Super thanks!
     
  6. NOMFET

    Thread Starter New Member

    May 26, 2010
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    Ok, had a bit of a mayday situation. First, the pictures:

    Code ( (Unknown Language)):
    1.  [URL="http://i303.photobucket.com/albums/nn153/mrpenguin1024/Powerboard/DSC00321.jpg"]Top Side[/URL]
    Code ( (Unknown Language)):
    1. [URL="http://i303.photobucket.com/albums/nn153/mrpenguin1024/Powerboard/DSC003201.jpg"]Bottom Side (Mirrored Horizontally)[/URL]
    This is what went down:

    TV wouldn't power on, no LEDs. Pull TV Apart, removed power board. Initial troubleshooting reads F801 as blown fuse (Yellow square, right side). Replaced T4AH250V fuse with same exact type, new pigtails. Plugged power supply board only to wall outlet (120v AC, marked as 2 teal squares, left bottom).

    Immediately after plugging in AC power, R102 (with pins GR26 and GR27) began glowing red, the ceramic cracked, and white smoke started rising. Of course I unplugged it quickly!

    So, This component is made of ceramic, the only markings I can find are "RCT071N 6R80JSMT". Google says this is a Rectangular Thermal Cutoff resistor Fuse....

    So what happened here? I have no idea....would I be better off just buying a new power board (about $80), or is it still fixable if I replace the RTCRF? Also, I seem to be treating the symptoms, not the cause....can someone advise me?

    Thanks in advance!
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Anyone? .......
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Hey :D..I was just messing with you.
    I can get you to fix that. no problem.
    But first I like to see a clear picture of the board from both sides.
    Take a high res picture with good lighting
    after that I can tell you what to do..
    No worries. :p
     
  9. NOMFET

    Thread Starter New Member

    May 26, 2010
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    You got an IM? :p (taking pics now)
     
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I don't do house calls :D.
    This place is the place to be
     
  11. NOMFET

    Thread Starter New Member

    May 26, 2010
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    Ok, here are more pics:

    Code ( (Unknown Language)):
    1. [URL="http://s303.photobucket.com/albums/nn153/mrpenguin1024/Powerboard/"]Photo Album of Power Board[/URL]
     
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Hmmm... So tell me every itsy bitsy detail of what happened and what the current status is.
    Just to make sure.
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I am seeing burned components what exactly happened?
    See the attached.
    I assume you are having a PSU shorted component.
    I will need a high resolution close up of that area. I need to see the details.
     
    Last edited: May 28, 2010
  14. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    Rif@@

    Attached is a 400% zoom. Are you thinking about R567 and the one below it showing signs of heat?
     
  15. NOMFET

    Thread Starter New Member

    May 26, 2010
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    All the little details are in my previous post... as for R567, its R667 and R665 (topside are two porcelin square things, MPR-5W R045JSMT") In between the legs of these are two diodes (D620 and D619). I can't read them as diodes still connected to the boards. Up close, they are still black and glossy, with "73" atop them.

    It would seem that the problem is isolated between the two fuses? (From AC in, to the fuse in electrical tape).

     
  16. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    the pic in post 13 is the complete area to see and to be clear when I zoom in to see the details. A high res pic will allow me to zoom in to identify the text, which I will need to make referrals

    As for the problem I will mark and tell you what to do in detail. If you want me to keep checking and helping it is imperative that you follow my lead.

    As this has happened before. If I a am leading you then you have to follow me and me only, I am telling this because you will see comment's and other methods as n00bs will come in and post telling to dd this and that. I know what I am doing and I do not need anyone else to tell me what to do.

    I am not telling not to comment, please do, as I will respond to that post if it needs to but it is up to you to decide what to do, if in doubt don't do, but ask before hand.

    I hope you have the talent to remove, solder and test components. Do not damage the board with too much heat and have proper tools with you. As I might ask you to do things that you have never imagined, I never have got this good if I did not do the things I do over the years. Don't worry my suggestions are 99% safe, well atleast to me :D. Though I might blow a fuse to be sure. Wht can I say it happens.

    There will be a lot who will be reading this and may comment. They are almost welcome but please keep to the subject.

    My response time is very unusual, as I am working always. I will see this to end. My time is way different from ur times and to keep I a always awake the whole night if any one is expecting me. No need to thank me, it's what I feel happy about and comfortable with. And if I did not respond it is that I am asleep. Or away from Male' attending to resort works.

    I will tell you to do measure AC live voltage and HV DC too. As SMPS tends to have these lethal voltage to begin with, I hope you are comfortable around High voltages. Plus you will need a good DMM.
    Please ask if in doubt. If I am online I will respond to the post almost immediately, keep in mind to refresh, and I hope you will post if you are doing something and later edit that post with details, so I will know to get on with my work and check every now and then.

    {ed}
    See attached
    First the area in the white square. I like to see a nice close up of that area from both sides. I have to be sure that, that SMPS have a PF ckt or not.

    Study the attached PIC and see the test points <T1:T6>
    These measurements are without power and assuming that the main fuse has blown.

    First temporarily short the points T1 & T4 with a 100 ohm 1W resistor for a few seconds and after that use a plier to short them, this will make sure that the reservoir cap is fully discharged.

    Second put the multimeter in the diode range and measure the forward voltage drop across T1 & T4 and note them. keep the meter connected for a few second to let the cap charge. Measure them both way with the probe

    Now measure T2 & T3. Note them

    Now measure the resistance between T5 & T6. Note them.

    Post ur results and fresh PIC's too to continue
     
    Last edited: May 29, 2010
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Joe... I like to see the whole board clearly always.
    thanks though ;)
     
  18. NOMFET

    Thread Starter New Member

    May 26, 2010
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    Pictures are uploading now to a new folder in my photobucket called "powerboard2", and readings as follows:

    Diode Ohms
    T1+/T4- = .496 296.6k
    T1-/T4+ = .361 13.74k

    T2+/T3- = 1.301 4.12m
    T2-/T3+ = 1.286 4.04m

    T5-/T6+ = No reading 4.64m
    T5+/T6- = No reading 5.40m
     
    Last edited: May 29, 2010
  19. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    For the time being remove the surge limiting resistor, it is open.
    I am checking the pics to see if the PFC is there, I'll edit this post soon.
    If you can remove the bridge too.
    Post back if you have a q?
    I am here.
     
  20. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Ur pics are not complete buddy.
    you have given me half of the PSU primary. PFC is on the top. See the pic I have marked the white square
     
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