Hello everyone. I'm trying hard to do a better job with my posts so this diagnostic was done STRICTLY BY THE NUMBERS! No short-cuts.
I picked up this Sharp LC-60LE600U with the complaint the TV would not turn on. The ICON would illuminate as soon as the TV was plugged in then go out about 10 seconds later, no backlights. I ran the fault bypass procedure before purchase and got the backlights to flash.
Voltage tests: Back at the shop I put the TV on a switchable power strip, switched it on and checked the main caps which rise to 405V then trail back off to 165V. The voltages below are reference chassis ground:
CONNECTOR “PD”
1….PNL_12V……..10V, rises to 11.84V, drops to 0
2….PNL_12V……..10V, rises to 11.84V, drops to 0
3….GND…………….Continuity to ground present
4….GND…………….Continuity to ground present
5….UR13.2V……...13.2V, drops to 0
6….UR13.2V………13.2V, drops to 0
7….UR13.2V………N/C
8….UR13.2V………N/C
9….GND…………….Continuity to ground present
10....GND………….Continuity to ground present
11….GND………….N/C
12….GND………….N/C
13….AC_DET…….3.3V, drops to 0V, raises back up to 2.15V
14….PS_ON………2.06V remains constant with AC 120V applied
15….BU5V………..5.03V remains constant with AC 120V applied
16….PNL_POW…0V, raises to 3.26V, drops to 0V.
17….PWM1………6/10V, raises quickly to 1.5V (max seen, varies), drops quickly to 0V
18….N/C
19….DIMMER…..N/C
20….N/C
21….OFL…………..N/C
22….ERROR………3.29V, drops to 0V
23….PWM2………N/C
24….STB……………0V, raises quickly to 3.24V, drops quickly to 0V
CONNECTOR L1 (backlight connector) IMPORTANT NOTE! Terminal 1-1 is on the RIGHT side of connector L1.
Term#..........Voltage (L1 seated)……………………..Voltage (L1 disconnected fr PSU)
1-1………83.5V, drops to 0V……………………………….….. 83.9V, drops to 0V
1-3…..…10V, raises to 40V, drops to 0V………………...-66.5V, raises to 0V
1-5……..83.5V, drops to 0V……………………………………. 83.9V, drops to 0V
1-7……..10V, drops to -25.8V, raises to 0V……….……-66.5V, raises to 0V
1-9……..78V, raises to 83V, drops to 0V………………... 80V, drops to 0V
1-11……10V, raises to 40V, drops to 0V………………..-66.5V, raises to 0V
1-13…….86.5V, raises to 150V, drops to 0V…………… 83.5V, drops to 0V
1-15…… 10V, raises to 30V, drops to 0V……………....-66.3V, raises to 0V
With that I tested the LED's at L1 with my backlight tester. It displays both volts and amps in the readout which are recorded below:
1-1 to 1-3: LEDs illuminate, 91.9V, 36.6mA
1-5 to 1-7: LEDs illuminate, 91.9V, 36.6mA
1-9 to 1-11: LEDs illuminate, 91.9V, 36.6mA
1-13 to 1-15: LEDs do not illuminate, 318V, 0mA
So it looks like there's an open at the LEDs driven by pins 1-13 and 1-15…but what about that 150V spike on the same line? That didn't seem right so I pulled the PSU and had a look at IC7201 and all the components in-circuit with it.
IC7201 is part number MP24830 and is described as a 4.5V – 90V Programmable Frequency White LED Driver, datasheet attached. The area of concern has to do with pins 3 (VDD) and 4 (INGND) of this IC. Between the circuits there is SMD MLCC capacitor location C7225. When testing across this cap or pins 3 and 4 of IC7201 it indicates short direct. When testing from pin3 or 4 to ground I get a low reading, .193 or so.
Final diagnosis: Open LED's causing TV to go in to fault protect, possibly associated with shorted cap C7225 and/or IC7201.
My concern is if I put backlights in and IC7201/C7225 are shorted that it will damage the new LED strip or the board itself.
So here are my questions:
It seems to me pins 3 and 4 of IC7201 should not be shorted since pin 3 is supply voltage and pin 4 is Input Ground Reference/Reference for the EN/DIM signal. Is this assertion correct?
Could the 150V spike at L1/ 1-13 to 1-15 be the result of either shorted capacitor C7225 and/or shorted IC7201 on pins 3 and 4?
The datasheet specifically calls for a capacitor to be placed on VDD and says “Needs C1 to prevent large input voltage spikes”. If I remove C7225 and find it short can I leave it off the board temporarily for a quick re-test, or should I replace the cap first?
I picked up this Sharp LC-60LE600U with the complaint the TV would not turn on. The ICON would illuminate as soon as the TV was plugged in then go out about 10 seconds later, no backlights. I ran the fault bypass procedure before purchase and got the backlights to flash.
Voltage tests: Back at the shop I put the TV on a switchable power strip, switched it on and checked the main caps which rise to 405V then trail back off to 165V. The voltages below are reference chassis ground:
CONNECTOR “PD”
1….PNL_12V……..10V, rises to 11.84V, drops to 0
2….PNL_12V……..10V, rises to 11.84V, drops to 0
3….GND…………….Continuity to ground present
4….GND…………….Continuity to ground present
5….UR13.2V……...13.2V, drops to 0
6….UR13.2V………13.2V, drops to 0
7….UR13.2V………N/C
8….UR13.2V………N/C
9….GND…………….Continuity to ground present
10....GND………….Continuity to ground present
11….GND………….N/C
12….GND………….N/C
13….AC_DET…….3.3V, drops to 0V, raises back up to 2.15V
14….PS_ON………2.06V remains constant with AC 120V applied
15….BU5V………..5.03V remains constant with AC 120V applied
16….PNL_POW…0V, raises to 3.26V, drops to 0V.
17….PWM1………6/10V, raises quickly to 1.5V (max seen, varies), drops quickly to 0V
18….N/C
19….DIMMER…..N/C
20….N/C
21….OFL…………..N/C
22….ERROR………3.29V, drops to 0V
23….PWM2………N/C
24….STB……………0V, raises quickly to 3.24V, drops quickly to 0V
CONNECTOR L1 (backlight connector) IMPORTANT NOTE! Terminal 1-1 is on the RIGHT side of connector L1.
Term#..........Voltage (L1 seated)……………………..Voltage (L1 disconnected fr PSU)
1-1………83.5V, drops to 0V……………………………….….. 83.9V, drops to 0V
1-3…..…10V, raises to 40V, drops to 0V………………...-66.5V, raises to 0V
1-5……..83.5V, drops to 0V……………………………………. 83.9V, drops to 0V
1-7……..10V, drops to -25.8V, raises to 0V……….……-66.5V, raises to 0V
1-9……..78V, raises to 83V, drops to 0V………………... 80V, drops to 0V
1-11……10V, raises to 40V, drops to 0V………………..-66.5V, raises to 0V
1-13…….86.5V, raises to 150V, drops to 0V…………… 83.5V, drops to 0V
1-15…… 10V, raises to 30V, drops to 0V……………....-66.3V, raises to 0V
With that I tested the LED's at L1 with my backlight tester. It displays both volts and amps in the readout which are recorded below:
1-1 to 1-3: LEDs illuminate, 91.9V, 36.6mA
1-5 to 1-7: LEDs illuminate, 91.9V, 36.6mA
1-9 to 1-11: LEDs illuminate, 91.9V, 36.6mA
1-13 to 1-15: LEDs do not illuminate, 318V, 0mA
So it looks like there's an open at the LEDs driven by pins 1-13 and 1-15…but what about that 150V spike on the same line? That didn't seem right so I pulled the PSU and had a look at IC7201 and all the components in-circuit with it.
IC7201 is part number MP24830 and is described as a 4.5V – 90V Programmable Frequency White LED Driver, datasheet attached. The area of concern has to do with pins 3 (VDD) and 4 (INGND) of this IC. Between the circuits there is SMD MLCC capacitor location C7225. When testing across this cap or pins 3 and 4 of IC7201 it indicates short direct. When testing from pin3 or 4 to ground I get a low reading, .193 or so.
Final diagnosis: Open LED's causing TV to go in to fault protect, possibly associated with shorted cap C7225 and/or IC7201.
My concern is if I put backlights in and IC7201/C7225 are shorted that it will damage the new LED strip or the board itself.
So here are my questions:
It seems to me pins 3 and 4 of IC7201 should not be shorted since pin 3 is supply voltage and pin 4 is Input Ground Reference/Reference for the EN/DIM signal. Is this assertion correct?
Could the 150V spike at L1/ 1-13 to 1-15 be the result of either shorted capacitor C7225 and/or shorted IC7201 on pins 3 and 4?
The datasheet specifically calls for a capacitor to be placed on VDD and says “Needs C1 to prevent large input voltage spikes”. If I remove C7225 and find it short can I leave it off the board temporarily for a quick re-test, or should I replace the cap first?
Comment