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Toshiba 55HT1U 5vdc unstable

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    #1

    Toshiba 55HT1U 5vdc unstable

    The set is dead. P802 Plug in the TV and the 5vdc is about 3.5vdc and constantly varies up/down and the 24vdc turns on. Unplug P802 at PS to main and the 5vdc is good and no 24vdc. I fugured that the Main board is bad loading the 5vdc. I had the TV PS and main board connected then tied in my B&K 1760 PS set to 5vdc and tied it into the main board along with the TV PS. voltage was a stable 4.7vdc but drawing 1.6 amps from BK PS. Again lead me to the main board.
    I got another board and exact same problem on initial test. 24vdc turns on and varying 3.5vdc at PS P802. Either I have two bad main boards or the
    PK101V1790I POWER SUPPLY is bad. What resistance and wattage should I use to load test the PS 5vdc. I want to rule out the PS before contacting the seller of the main board. Bright side is all four inverter boards dont load the 24vdc
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    #2
    Re: Toshiba 55HT1U 5vdc unstable

    Hi,
    Just looked on the Owner's manual for 55HT1U and they say the stand-by is only 0.6 W, so at this wattage, the mainboard should draw ~ 120 mA. Your 1.6 A drawn from the BK PS is way too much for a stand-by mode, so this points out to a mainboard issue IMHO.
    In a transistor circuit protected by a fuse, the transistor will always blow to protect the fuse.

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      #3
      Re: Toshiba 55HT1U 5vdc unstable

      One thing to eliminate is things like the IR keypad and receiver. If they are shorted, conceivably it could bring down main supply.
      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

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        #4
        Re: Toshiba 55HT1U 5vdc unstable

        I search and found this post on esting the 5vdc.
        https://www.badcaps.net/forum/showthread.php?t=24304
        Using a 10 ohm 10 watt resistor the power supply voltage was 2.5vdc and varies when not connected to the Main board. This points to the PS. But the previous test points to the Main board with the original and the replacement are both bad. I ordered a recycled PS.
        Possible a bad PS or a bad PS and two bad Main board. I hate this kind of problems
        Last edited by Ltank; 08-11-2014, 12:38 PM.

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          #5
          Re: Toshiba 55HT1U 5vdc unstable

          I applied 5vdc to the Main board by it self. It was not loaded down current draw on PS
          displayed .04 amps. Is it possable the TV PS is bad and loads the external PS down ?
          I now have more questions than answers

          Comment

            #6
            Re: Toshiba 55HT1U 5vdc unstable

            It is unlikely, but conceivably possible. Try just the PSU only?
            Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
            For service manual, schematic, boardview (board view), datasheet, cad - use our search.

            Comment

              #7
              Re: Toshiba 55HT1U 5vdc unstable

              Power Supply by it self unloaded is 5Vvdc/. Loaded using a 10 ohm 1 watt resistor connected one side to gnd and the other to the standy 5vdc pin the voltage is almost
              3.5 vdc and varies

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                #8
                Re: Toshiba 55HT1U 5vdc unstable

                I could not find a schematic for PS. I made the usuall diode, transistor, transformer and mosfet checks. I ordered a PS for 35 bucks and it works fine. The Power surge had taken out HDMI ports one and two and the 5 standby on PS. The original Main board would not show signal through the ports. The main board I ordered worked fine,

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