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Sharp LC-32AX5M power board RDENCA182WJQZ

Discussion in 'Troubleshooting and Repair' started by Timescope, Aug 30, 2012.

  1. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    Hello everyone,

    I am a new member, kindly asking for your help with a Sharp Aquos LC-32AX5M power supply board RDENCA 182WJQZ.

    1. What is the part number of IC101, the pwm controller that regulates the 5v, 10v and 13v supplies? It is a soic-8 pin surface mounted ic soldered under the pcb on the primary side near the three opto-isolators PC 101, PC102 and PC103.

    2. What is the part number of Q304 ? It is a small surface mounted "transistor" located near the three opto-isolators on the secondary side and drives the middle one, PC102.

    The pinout of IC101 is the same as the NCP1203 etc series or the FA5571. The problem I have is the operation of pin 1( the latch/skip cycle etc) which is pulled up to the Vcc (pin 6) of IC101 through a 1K resistor and the photo-transistor of the opto-isolator PC102 on the primary side when it is turned on by the led on the secondary side. On the secondary side,the led of this opto isolator is turned on with Q304 which looks like a common emitter npn configuration with the "emitter" connected to ground and the "collector" pulls the cathode of the led low ( the anode is connected to the 6v supply by a !K resistor). The "base" has the following connections: 10k to ground, 1k to +6v and 1k to the backlight inverter supply 24v so it must be a non-inverting device or IC101 will be latched off .

    For some reason, the power supply diagram is not included in the numerous service manuals I have downloaded for this set and others in the series.

    Any help would be appreciated,
    Thanks in advance,
    Timescope.
     
  2. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    Unknown device

    Hello everyone,

    Does anyone know a device that would turn the led off when the input is 24v and on when the input is zero volts in the attached circuit ?

    Thanks,
    Timescope.
     

    Attached Files:

  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    Well, it is clear what the control terminal is.

    Determine the range of voltages available at this terminal if the control terminal is an open circuit.

    Then determine the range of currents available if it were a short to ground.

    These together will tell you which of the two obvious candidate components it is.
     
  4. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    3 volts when Vin = 0 if control is an open circuit
    15v when Vin =24v if control is an open circuit
    If the control terminal is short circuited to ground, input current = 24 mA when Vin =24v
    When Vin = 0v , Thevenin source = 500 ohms in series with 3v.

    Timescope
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
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    Jan 21, 2010
    The two most likely components are a BJT or a MOSFET.

    Which one will turn on and off in this circuit?

    That is your answer.
     
  6. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    Hi (*steve*),

    Please note that the LED should be OFF when the 24v is present. That would imply a non-inverting device.Bipolar and mosfets are inverting.

    Timescope.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
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    Jan 21, 2010
    OK, I read that backwards.

    When Vin is floating, is the LED supposed to be on or off?
     
  8. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    Hi (*steve*),

    Vin is the back light inverter supply. The power sequence is:
    PS_ON = H switches 6v to the main board and enables the PFC and 24v supplies (via an opto-isolator PC103 ). The 24v supply switches a relay that shorts the NTC thermistor in series with the mains and should turn off the opto-isolator (PC102) that puts the main supply PWM controller in skip cycle mode during standby .
    Please check my Aug 30th post. Pin 1 is also connected to a P6KE440A in series with 33k ohms that senses over voltage on the rectified mains smoothing capacitors.
    I have looked at devices like APE6809 to12, APR 3001, 3002, 3003 but the pin connections do not correspond.
    I am currently using TinyCad to transfer the complete circuit from paper and will post it when finished.
    Thanks for responding.
    Timescope.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    Does this do anything other than turning on/off the LED?

    I wonder if it is a voltage detector chip? (so the LED indicates a low 24V rail)

    Does it have anything written on it? What package is it in?
     
  10. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    The LED is in the opto-isolator PC102 and my attachment shows all the connections to the device.

    The PC102 phototransistor emitter is connected to pin 1 of the PWM control ic on the primary side and it's collector is connected to pin 6 (Vcc) via a 1 K ohm resistor.

    The power board had been sent overseas for a replacement which was not purchased and the component in question probably broke off the board due to rough handling. The PWM control ic part number is not visible. The unknown device package is a 3 pin SOT-23 like a small smd transistor and the schematic I attached shows how the pins are connected: input on the left, ground on the right and the output to the opto-isolator center.

    Thanks,
    Timescope.
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    Oooh, that's a bit ugly.

    It sounds like this is part of the feedback loop for the power supply.

    What you *may* be looking for is a voltage detector chip that pulls the output low when the input is below 15V. And I can't locate any SOT-23 devices with that sort of specs.:(
     
  12. Timescope

    Timescope

    43
    0
    Aug 30, 2012
    Hi (*steve*),
    It is really a mysterious device. I went through the smd code book and looked through 80 Sharp manuals for various models but could not find any matching device. I'll just have to cook something up.
    Thanks a million for responding,
    Timescope.
     
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