Hello,
I would be really grateful for your suggestion how to repair a no backlight power on TV LG39LN575S. There is a visible menu on a screen when I use external torch (so logic board and panel works correctly), there is just no backlight.
I have connected a logic board which is turning on power board and disconnected LED backlight cable.
Power board:
REV2.0 2013.03.28
PCB: EAX64905301(2.2)
LGIT PCB P/N: 3PCR00184A
IC LED driver MAP3202
MAP3202 voltages:
(1) EN = 2.75V
(2) VCC = 12.05V
(3) GATE = 0 V
(4) GND = 0 V
(5) CS = 0 V
(6) RT = 3.04 V
(7) SYNC = 0 V
(8) REF = 5.2 V
(9) PWMO = 0 V
(10)OVP = 2.8 V
(11)PWMI = 0.49 V
(12)COMP = 0 V
(13)FBP = 0.82 V
(14)FBN = 0 V
I have measured some values resistance (yellow) and voltages (green) (please check the attachment).
I was NOT able to get the right power board schematic for my power board EAX64905301(2.2), so maybe attached schematic does not match to my TV!
From a datasheet:
My value of PWMI is 0.49V
Do you think that MAP3202 is just sleeping because of wrong outside situation or is it broken?
Do you have any ideas what can be wrong?
What else I can measure?
Are you able to get a right schematic for my power board?
I guess GATE and PWMO should be oscillating and have non zero value.
If there is no short between PWMO and GND, it means outside circuit should not block PWMO output, or am I wrong?
Do you have any presentation/testing of MAP3202 which describe how it works (on oscilloscope)?
I guess it should work as a https://en.wikipedia.org/wiki/Buck_converter, so both transistors on GATE and PWMOshould oscillating at the right time. And there should be non zero voltage.
Update:
So, as far as I understand that it is using FBP to control a current on output (to power LEDs), that current is set to max LED brightness.
To control of backlight intensity it is using external PWM Dimming, which should oscillating. In my case there is a constant value of PWMI which is 0.49V and it means, there is no oscillation !!! And as PWMO just copy logical state (zero/one) of PWMI, they are doing nothing as PWMI is a constant.
Am I right? Is there a way how to disable PWM dimming and use just FBP based control of output current? Just to check whether there will be regular output voltage.
Can it work (is there an output voltage) if output load (LED diodes) are not connected?
Thank you ;-)
I would be really grateful for your suggestion how to repair a no backlight power on TV LG39LN575S. There is a visible menu on a screen when I use external torch (so logic board and panel works correctly), there is just no backlight.
I have connected a logic board which is turning on power board and disconnected LED backlight cable.
Power board:
REV2.0 2013.03.28
PCB: EAX64905301(2.2)
LGIT PCB P/N: 3PCR00184A
IC LED driver MAP3202
MAP3202 voltages:
(1) EN = 2.75V
(2) VCC = 12.05V
(3) GATE = 0 V
(4) GND = 0 V
(5) CS = 0 V
(6) RT = 3.04 V
(7) SYNC = 0 V
(8) REF = 5.2 V
(9) PWMO = 0 V
(10)OVP = 2.8 V
(11)PWMI = 0.49 V
(12)COMP = 0 V
(13)FBP = 0.82 V
(14)FBN = 0 V
I have measured some values resistance (yellow) and voltages (green) (please check the attachment).
I was NOT able to get the right power board schematic for my power board EAX64905301(2.2), so maybe attached schematic does not match to my TV!
From a datasheet:
The MAP3202 offers the features such as Under Voltage Lock Out (UVLO), Boost current limit, Over Voltage Protection and Short Current Protection of LED (SCP).
My value of PWMI is 0.49V
PWMI input low voltage < 0.8V
2.0V < PWMI input high voltage < 5.5V
1. Under Voltage Lock Out (UVLO)
When VCC voltage reaches over 8V, UVLO starts operating
which enables Internal 5V Regulator, making all internal control
circuits including oscillator, gate driver and protection circuit
ready for operation and output pin of GATE, PWMO and
COMP starts operating depending on the input status of PWMI.
2. PWM Dimming
The MAP3202 makes same phase PWMO output from logic
PWM signal of PWMI using internal Level shift. PWMO of
operating voltage level is between GND and VCC.
2.0V < PWMI input high voltage < 5.5V
1. Under Voltage Lock Out (UVLO)
When VCC voltage reaches over 8V, UVLO starts operating
which enables Internal 5V Regulator, making all internal control
circuits including oscillator, gate driver and protection circuit
ready for operation and output pin of GATE, PWMO and
COMP starts operating depending on the input status of PWMI.
2. PWM Dimming
The MAP3202 makes same phase PWMO output from logic
PWM signal of PWMI using internal Level shift. PWMO of
operating voltage level is between GND and VCC.
Do you think that MAP3202 is just sleeping because of wrong outside situation or is it broken?
Do you have any ideas what can be wrong?
What else I can measure?
Are you able to get a right schematic for my power board?
I guess GATE and PWMO should be oscillating and have non zero value.
If there is no short between PWMO and GND, it means outside circuit should not block PWMO output, or am I wrong?
Do you have any presentation/testing of MAP3202 which describe how it works (on oscilloscope)?
I guess it should work as a https://en.wikipedia.org/wiki/Buck_converter, so both transistors on GATE and PWMOshould oscillating at the right time. And there should be non zero voltage.
Update:
So, as far as I understand that it is using FBP to control a current on output (to power LEDs), that current is set to max LED brightness.
To control of backlight intensity it is using external PWM Dimming, which should oscillating. In my case there is a constant value of PWMI which is 0.49V and it means, there is no oscillation !!! And as PWMO just copy logical state (zero/one) of PWMI, they are doing nothing as PWMI is a constant.
Am I right? Is there a way how to disable PWM dimming and use just FBP based control of output current? Just to check whether there will be regular output voltage.
Can it work (is there an output voltage) if output load (LED diodes) are not connected?
Thank you ;-)
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