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Need guidance on SMPS repair

Discussion in 'Electronic Repair' started by BFriedl, Dec 5, 2003.

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  1. BFriedl

    BFriedl Guest

    Hi...me again. So I've got this Mitsubishi VS-6015R V10 chassis tv that
    has a bad power supply. I broke it into two parts, since there are two
    switching IC's. Got the first part done (STR-S6301) and get +130v with a
    75w load. Yay! Now that I understand how switch-mode supplies work, the
    second part is a bit confusing because there is no feedback control. It
    seems that the STR-S5041G is not switching?? Correct me if I am wrong. I
    have uploaded a scan of the schematics with some modifications done in
    mspaint. Each component with a blue square next to it has been replaced.
    The section not working is surrounded with a large red square.
    <A
    HREF=http://www.acbow.com:8080/v10Power.jpg>http://www.acbow.com:8080/v10Power.jpg</A>
    http://www.users.qwest.net/~wfriedl/v10Power.jpg

    Sorry in advance for the long post, but here go the questions, starting
    at the top of the schematic:
    1. What is the difference between the two grounding
    types shown at the right corner? The one with ///
    seems to be used the most.

    2. Im a bit confused as to the function of the cap in the yellow circle.
    Through troubleshooting, I noticed that the ground on connector PA and
    PK is not the same as ground on connectors PC. Could this be because the
    circuit that feeds connector PC also feeds PF? (PF is always on, and
    ground from PF is same ground as PC.) I noticed that the cap circled is
    what bridges these two grounds together.

    3. How do i troubleshoot this half of the supply? Heres what I've gotten
    with a 25w load:
    Connector PA
    Pins 1 & 2: +26V; should be +24V
    Pins 3 & 2: -24V; good
    Connector PK
    Pins 1 & 2: +29V; should be +28V (good?)
    It appears that pin 3 does not ground with pin 2 here, but when
    connected to pin 2 of PC, I get -16V; should be -12.
    Connector PC
    Pins 1 & 2: +16V; good
    Pins 3 & 2: -17V; should be -16V (good?)

    4. Now that ive broken it down that way, it seems that everything is
    running correctly except for pin 3 of connector PK. Also noticed that
    voltages for PF at top are quite high as well; pins 4 read +18V with 25w
    load, +30v without load.

    --
    BFriedl
    A+ Certified Technician
    AIM: UACybercat
    ** Bear Down Arizona! **
    ******* Go Cats! *******
     
  2. BWL

    BWL Guest

    Looks to me like power supply is working fine. Low voltage supply does not
    regulate all voltages. As long as they're that close, it should work. If TV
    still won't power up, you've got either a bad vertical IC, and possibly some
    bad caps in it's circuit, or possibly a bad dynamic focus IC on convergence
    board. To check for bad focus IC, unplug the PA connector and see if it will
    start. To check the vertical IC (LA7838), either replace it or check pin1
    (should be 9 to 12v), pin 8 (28v), pin 13 (28v), and pin 12 (13.5-14.5v). Pin
    12 is the output, and may not show much for a second or two. If the set isn't
    making ANY High Voltage, the Horiz Output may have been blown by runaway 130v.
     
  3. BFriedl

    BFriedl Guest

    Looks to me like power supply is working fine. Low voltage supply does not
    PLEASE MAKE ALL REPLIES TO NEW THREAD:
    "Mits VS6015R (again) almost fixed; what next?"

    When turned on before I started troubleshooting, I got no HV and no
    sound. All I heard was a click sound of main relay turning on. First
    thing to go were some inductors on the convergance board. So perhaps it
    is the bad dynamic focus IC? Should I try powering this set on without
    convergance board in set? Or are there some caps on the vert board that
    need checking first?
    TIA,
    Brian

    Here is a repost of March, 2002:

    "I was having wiring problems in my house for"
    "about 2 months and it recently tripped the"
    "circuit breaker. When the power was fixed, I"
    "powered up my TV (was on this same circuit)"
    "some smoke started to billow out of the front"
    "grille below the screen. I took off the black"
    "cover and found the convergance board with some"
    "fried inductors on it."
    ""
    "Could this have been caused by my power problems,"
    "slowly eating away at it with the constant sags"
    "and surges?? Or did the ps go bad?"
    "Brian"

    --
    BFriedl
    A+ Certified Technician
    AIM: UACybercat
    ** Bear Down Arizona! **
    ******* Go Cats! *******
     
  4. BFriedl

    BFriedl Guest

    From thread "Need guidance on SMPS repair"
    When turned on before I started troubleshooting, I got no HV and no
    sound. All I heard was a click sound of main relay turning on. First
    thing to go were some inductors on the convergance board. So perhaps it
    is the bad dynamic focus IC? Should I try powering this set on without
    convergance board in set? Or are there some caps on the vert board that
    need checking first?
    TIA,
    Brian

    Here is a repost of March, 2002:

    "I was having wiring problems in my house for"
    "about 2 months and it recently tripped the"
    "circuit breaker. When the power was fixed, I"
    "powered up my TV (was on this same circuit)"
    "some smoke started to billow out of the front"
    "grille below the screen. I took off the black"
    "cover and found the convergance board with some"
    "fried inductors on it."
    ""
    "Could this have been caused by my power problems,"
    "slowly eating away at it with the constant sags"
    "and surges?? Or did the ps go bad?"
    "Brian"

    --
    BFriedl
    A+ Certified Technician
    AIM: UACybercat
    ** Bear Down Arizona! **
    ******* Go Cats! *******
     
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