Monday, January 04, 2016

SHARP LC-42DH77E Service mode troubleshooting and power supply circuit diagram – LCD television repair

Category: LCD Television Repair 

Contents of this article 

  • How to access service mode
  • Troubleshooting 
  • 24V Power supply circuit diagram 


In order to reach service menu, First Press “MENU” Then press the remote control code two times, which is “4725”.
Analog - Digital SW update via USB
1. Please copy the files to USB (root).
#  mb60_en.bin
#  mboot.bin
#  usb_auto_update.txt
2. Turn power to OFF by mechanical switch(rocker switch) or removing AC plug. And plug the USB to TV
3. Keep pressing OK key from remote controller and then turn the TV power to ON(by mechanical switch or by inserting the AC plug) and keep OK key pressed until the stanby led blinks rapidly(rapid blinking is faster than normal blinking)
4. When the led is started to blink rapidly, you can release the OK key.Please wait approximately for 1-2 minutes.
5. When the blinks of led is stopped, TV opens autamatically with the new SW.
No Backlight Problem
If TV is working, led is normal and there is no picture and backlight on the panel.
Possible causes: Backlight pin, dimming pin, backlight supply, stby on/off pin Backlight pin should be high in open position. If it is low, please check Q181 and panel cables.
Dimming pin should be high or square wave in open position. If it is low, please check S16 for Mstar side and panel or power cables, connectors.
Backlight power supply should be in panel specs. Please check CN705 for MB60, related connectors for power supply cards.
STBY_ON/OFF should be low for standby on condition, please check R1677.
CI Module Problem
CI is not working when CI module inserted.
Possible causes: Supply, supply control pin, detect pins, mechanical positions of pins CI supply should be 5V when CI module inserted. If it is not 5V please check CI_POWER_CTRL, this pin should be low.
Please check mechanical positions of CI module.
Detect ports should be low. If it is not low please check CI connector pins, CI module pins and 3V3_VCC on MB60.
Led Blinking Problem
Problem: LED blinking, no other operation
This problem indicates a short on Vcc voltages. Protect pin should be logic high while normal operation. When there is a short circuit protect pin will be logic low. If you detect logic low on protect pin, unplug the TV set and control voltage points with a multimeter to find the shorted voltage to ground.
IR Problem
Problem: LED or IR not working
Check LED card supply on MB60 chassis.
Keypad Touchpad Problems
Problem: Keypad or Touchpad is not working
Check keypad supply and KEYBOARD pin on MB60.
USB Problems
Problem: USB is not working or no USB Detection.
Check USB Supply, It should be nearly 5V. Also USB Enable should be logic high.
No Sound Problem
Problem: No audio at main TV speaker outputs.
Check supply voltages of VDD_AUDIO, 5V_VCC and 3V3_VCC with a voltage-meter.
There may be a problem in headphone connector or headphone detect circuit (when headphone is
connected, speakers are automatically muted). Measure voltage at HP_DETECT pin, it should be 3.3v.
No Sound Problem at Headphone
Problem: No audio at headphone output.
Check HP detect pin, when headphone is. Check 5V_VCC and 3V3_VCC with a voltage-meter.
Standby On/Off Problem
Problem: Device cannot boot, TV hangs in standby mode.
There may be a problem about power supply. Check 12V_VCC, 5V_VCC and 3V3_VCC with a voltagemeter. Also there may be a problem about SW. Try to update TV with latest SW. Additionally it is good to check SW printouts via hyper-terminal (or Teraterm). These printouts may give a clue about the problem.
No Signal Problem
Problem: No signal in TV mode.
Check tuner supply voltage; 5V_TUN. Check tuner options are correctly set in Service menu. Check AGC voltage at RF_AGC pin of tuner.
NCP1392B -High-Voltage Half-Bridge Driver
The NCP1392B/D is a self−oscillating high voltage MOSFET driver primarily tailored for the applications using half bridge topology. Due to its proprietary high−voltage technology, the driver accepts bulk voltages up to 600 V. Operating frequency of the driver can be adjusted from 25 kHz to 480 kHz using a single resistor. Adjustable Brown−out protection assures correct bulk voltage operating range. An internal 100 ms or 12.6 ms PFC delay timer guarantee that the main downstream converter will be turned on in the time the bulk voltage is fully stabilized. The device provides fixed dead time which helps lowering the shoot−through current.
Pin #
Pin Name
Pin Description
The driver accepts up to 16 V (given by internal zener clamp)
Connecting a resistor between this pin and GND, sets the operating frequency


Detects low input voltage conditions. When brought above Vref_EN, it stops the
driver. Operation is restored (without any delay) when BO pin voltage drops
100 mV below Vref_EN.

Drives the lower side MOSFET
Connects to the half−bridge output
Drives the higher side MOSFET
The floating supply terminal for the upper stage