Dell E190Sf LCD Monitor – How enter Service Mode – SMPS schematic

Factory mode – SMPS circuit diagram and working principle – DELL E190s – LCD Monitor

Factory Mode 

With signal input, press “Power” button to turn off the monitor. Press “Menu” and “Auto/Plus” buttons together, and then press “Power” button to turn on the monitor. 

After power on, press “Menu” button to call out Main Menu 

Pull down to Factory Reset and choose Factory to enter Factory mode.

Panel: JT094: Current using panel part number (DELL supply)

Exit: Exit from Factory mode and back to Reset to Factory Settings.

Auto Color: Automatically calibrate chip ADC parameters by using internal DAC. (Only with Burn-in ON) 

Burn In: Enable or disable the Burn-in mode by choosing ON or OFF. 

Reset Timer: Reset the “Turn-on time” of the panel to 0H0M. 

Color Temp: The R, G, B of Blue Preset (9300K), Red Preset (5700K) and Normal Preset (6500K) are generated from scaling chip’s back-end white-balance program. 

Time: Turn-on time of the panel.

Burn-in pattern: If it is a new monitor without VGA cable plugged in, burn-in pattern will self-generate automatically. Burn-in pattern will not be stopped until plugging in the VGA cable. Then, press “Menu” button to call out OSD Main Menu; pulling down to Factory Reset item and execute All Resetting to disable Bun-in ON.

Auto Color Balance (Automatically calibrate chip ADC parameter by using chip internal DAC.).  If it is a new-built set, press “Auto/Plus” button to execute “Auto Color” at 32gray scale pattern.

Confirm the following steps to perform “Auto Color Balance”: - Connect the VGA cable with the standard video pattern generator and display 32gray scale pattern on the monitor.

- Press “Power” button to power off the monitor.

- Press “Menu” and “Auto/Plus” buttons simultaneously; then press “Power” button to power on the monitor.

- Press “Menu” button, pull down to Factory Reset and choose “Factory” item.

- Set Burn In to ON, then execute Auto Color. - With “Auto Color” finished, return to Reset to Factory Settings OSD and execute All Settings to enable burn-in OFF.

EDID (Rewrite EDID data to EEPROM by Fox_VEDID_Programmer) The Write-Protect Pin of EEPROM is generally pulled up to enable EDID to be read only; EDID cannot be written at that status. 

The following steps enable EDID to be write:

Connect the monitor and PC via a VGA cable.

 Execute Fox_VEDID_Programmer. 

- Click “browse” icon to choose a binary file from the PC. 

- Type the “Serial Number” in the dedicated field. Each monitor will have its own serial number. Then click Enter on the keyboard to jump to next field. 

- Type 1 to 2 characters or digits in “Travel Card SN” field. Then click Enter to start writing EDID to monitor. 

- “PASS” will be shown with EDID finished programmed. Please plug out the AC power cord of the monitor to restart.

Upgrade Firmware to Serial via Flash Cable by Fox_VISP_Programmer 

Connect the monitor and PC via a VGA cable.

Fox_VISP_Programmer enables users to upgrade the firmware of the monitor directly through the VGA cable of a PC. Please follow the steps for reprogramming the firmware: 

- Click “Select Bin” icon to choose a binary file from the PC. The path of the selected binary file will be shown in the “Message” text window. Meanwhile, the checksum of the binary file will be calculated and displayed. 

- Click “Connect” to check if the connection is satisfactory between the monitor and PC. 

- If the connection is ready, click “Auto Programming F2 key” to begin flashing the firmware. During the flashing process, the motherboard of the PC will send out tick sound. If the firmware is reprogrammed successfully, “Command: Fast flash write successful” will be shown in the “Message” text window. The “successful update” condition will make the motherboard bring “Do-Re-Mi” sound five times with the interval of 500ms.

With the process of reprogramming firmware finished, plug out the power cable to restart the monitor.* The detailed reprogramming procedures will be described in Fox_VISP_Programmer User Manual.

Diagnostic Test Pattern

1. Press “menu”and “+”simultaneously and hold for 2 sec to enter to the diagnostic.

Check for line defects from the gray color test screen.

2. Press “+”to advance to the next test pattern - Red color screen. Check for partial block dot(s) - Red color dead pixel. Continue this for the Green & Blue color.

3. When in White color test screen, check for white color uniformity and if there white color appears greenish/reddish, etc.

If you change the M/B, be sure that the U301 and U402 these two components also changed to the new M/B because there was program inside. If not, please re-write EDID or upload firmware into serial flash(U402) via VGA Cable. 

If you adjust clock and phase, please do it at condition of Windows shut down pattern.

Confirm the R/G/B color under 32gray scale pattern.

 This LCM is analog interface. So if the entire screen is an abnormal color that means the problem happen in the analog circuit part, if only some scale appears abnormal color that stand the problem happen in the digital circuit part.

 If you check the H/V position, please use the crosshatch pattern.

 This LCM support 10 timing modes, if the input timing mode is out of specification, “Cannot Display this Video Mode” will be displayed on the screen.

 If brightness uneven, repairs Inverter circuit or change a new panel.

 If you find the vertical line or horizontal line lost on the screen, please change panel.

If the self-test pattern is moving on the screen, please check whether VGA Cable is plugged in the Monitor or PC. If the VGA Cable is plugged in well, please change another VGA cable.

SMPS (Power Supply Regulator Circuit Diagram)

Inverter Control circuit operations

DC_5V through R1 and C1 will provide power for U1 on the pin2(VDDA),When the voltage at VDDA is less than ~3.4V,the IC will enter the lockout mode. The IC will resume operation when the voltage at pin VDDA exceeds an approximate 3.8V threshold.

Pin3(SEL) used to select appropriate drive topologies, connecting pin SEL to GED shows the IC in the push-pull configuration..

SSTCMP (pin14) applys the soft-start function and the loop compensation funtion.C5 at SSTCMP compensates the feedback loop and provides good transient response to load changes.  When the IC is enabled, it starts from the stinking mode and the TIMER (pin8) is activated. During lamp

ignition,if the voltage at pin SSTCMP exceeds an approximate 2.0V threshold, the drive frequency will switch from stinking frequency to the operation frequency, The striking frequency is determined by (R4& R5) connected to Pin 4(RT1)and Pin5(RT). The operating frequency is determined just by R4.

Applying a voltage level greater than 2V from IF BD to pin6(PWM) can enable the IC, Once the voltage less than ~1.0V for longer than 20ms will disable the IC.

Once the lamps are ignited and the voltage at pins ISEN1(pin9),ISEN2(pin10),OLP1(pin12),and OLP2(pin13) all exceed approximately 0.8V,the IC enters the normal operation mode and the PWM dimming control is activated. During start up, ISEN1 (pin9and pin10) senses the voltage on the transformer secondary. If no current is sensed approximately 2 seconds, U1 shuts off. re used to limit current. C3 is used to dump noise.

DRV1 and DRV2 of U1 are used to drive Q1. DRV1 and DRV2 are controlled by build-in PWM IC.  Q1 is switched which has two build-in IGBTs. The working principle of circuit of T1, the same to circuit of Power.

The voltage signal on negative pole of D1 sensed through R7/R8 comes to Pin11 of U1 VSEN (Lamp Current Detection & Control). The CCFL current is detected through R12/R21 and reaches a regulated value. The CCFL current detected at resistor R12/R21 is converted to a voltage level and input to the ISEN1/2 Once the CCFLs are ignited and current is sensed through resistor R12/R21, performs the loop compensation function. The voltage at IC pin12 controls the drive duty cycle of the power MOSFETs to regulate the CCFL current.

Output Circuit and Protection Circuit operations

The transformer (T1) secondary winding leakage inductance and output capacitance(C22) forms a lower pass filter, which converts the square-wave driving signal into a sinusoidal output voltage signal for CCFL.

The over-voltage protection feature is implemented by using an external capacitor devider(C20/C21) to sense the output voltage. The divide-down voltage signal is sent to the IC Pin11 (VSEN) ,thus regulating the output voltage at the transformer secondary.

If a CCFL is removed, fails or damaged during normal operation, CCFL current is no longer sensed and the voltage on ISEN1/ISEN2 drops. Once the voltage at the ISEN1/ISEN2 pin is less than the lamp” on” threshold, the shutdown timer is activated. The IC maintains the output voltage for approximately 2-3seconds and once the timer reaches a threshold of approximately 3V, the IC will shutdown. 

To restart the IC, either toggle the SST_CMP pin or recycle the power on the VDDA pin.

High Voltage to Low Voltage Control Circuit

D850 is a rectifier in which there are 4 build-in diodes, inverting AC to DC.

C854 is used to smooth the wave from rectifier. R852 is a fuse resistor to protect the following circuit when inrush current is too large.

U850 is a current-mode PWM controller with excellent power-saving operation, It features a high-voltage current source to directly supply the startup current from bulk capacitor and further to provide lossless startup circuit. Max start-up current for U850 is 100 uA, When current flow from the bulk capacitor C854 through R843 and R842 gets to HV pin to start up U850, Meanwhile, the VCC supply current is as low as 100 uA thus most of the HV current is utilized to change the VCC capacitor C855

Whenever the Vcc voltage is higher than UVLO (16V), the GATE pin will output signal to drive the power MOSFET(Q850), the high-voltage current source is off and the supply current is provided from the auxiliary winding of the transformer PIN5.

When U850 begins to operate Pin8 of U850 will output square wave to drive Q850, then the main current flow get to GND bypassing through T850, Q850. Because of the change of current flow, wires in the other side of T850 will induct current. In the same time, the current inducted by wires which connected T850 Pin 1 and Pin 3, with components of D852, R856 and C855 ,will be supplied to U850 for normal operating.

The typical current mode PWM controller feedbacks both current signal and voltage signal to close the control loop and achieve ragulation.U850 detects the Q850 current from I sense pin which max voltage is set as 0.85V, then the Q850 current can be calculated as: I peak=0.85V/R869,When the sense voltage across the sense resistor R869, reaches the threshold voltage over 0.85V, the output GATE drive will be turned off. R849 and C846 is used to avoid the Isen pin damaged by the negative turn-on spike.

The voltage feedback signal is provided from the TL431(I851) through the I850 to the COMP pin. When the voltage on COMP pin is lower than 1.2V,the IC will turn off.

When Q850 is turned off, the main current flow will be consumed through D851, C875, R880, this will prevent Q850 from being damaged under large current impulse and voltage spike.

RT pin is to program the switching frequency ,by connecting R846 to ground to set the switching frequency,f=(65.0/R846)*100(KHz)

DC12Vand DC 5V Output Circuit and Feedback circuit

D854 is used to rectify the inducted current. R862 and C861 are used to store energy when current is reversed. The parts including C862, C865 and L852 are used to smooth the current waves that are from D855, then 13V voltage is supplied.
D856 and D857 are SCHTKY diodes used to rectify the inducted current.C866 and R866 are used to store energy when current is reversed, The components including C864,C874,C875,L851 and C876 are used to smooth the current waves, then DC+5V voltage is supplied. F851 is used for OCP for the LPS test.
DC 5V supply voltage feed back to PWM controller U850 via R861,R860,R859,C859,I851,R857, R863 used to control the voltage feedback loop.