Sharp LC-60LE600U won't stay on

[dpolk]

I am trying to fix a Sharp LC-60LE600U TV. When plugged in the center icon will light and after 8 secs the backlight will turn on bright for split sec, then dim for split sec and the turn off. The center icon will turn off after 15 sec from power on. The center icon doesn't flash any error codes. I've tried the "input" "vol" reset, no luck.

With everything connected, here are the dc voltages I am getting out of the "PD" connector to main board.
P1- 12vdc, drops out as soon as BL turns off.
P2- 12vdc, just before BL turns on and slowly fades after BL turns off.
P3- 0
P4- 0
P5- 13.2vdc at plug in. Drops off after BL turns off.
P6- 13.2vdc at plug in. Drops off after BL turns off.
P7- 13.2vdc at plug in. Drops off after BL turns off.
P8- 0
P9- 0
P10- 0
P11- 0
P12- 0
P13- 3.36vdc at plug in, drops off after BL turns off
P14- 2.12vdc at plug in and stays on.
P15- 5vdc at plug in and stays on.
P16- 3.2vdc just before BL comes on and drops off after BL turns off
P17- jumps all over, up to 1vdc at plug in, to 0.3 at BL on, to 0 after BL turns off
P18- 0
P19- 0.09 at BL on
P20- 0
P21- 0
P22- 3.28vdc at plug in, drops to 0 when BL comes on.
P23- 0
P24- 3.2vdc at BL on, drops off after BL turns off.

R7900 - 2.4 ohm in the board
D7905 - open one way, 556 other way in board

Any ideas on what to test next? How do I tell if my Power Board is bad or my main board is bad? Please keep it simple, I'm a mechanical engineer.

[budm]

Re: Sharp LC-60LE600U won't stay on

Please put the pin name for each pin of that PD connector so we can easily see what Voltage we should expect from each pin.

[dpolk]

Re: Sharp LC-60LE600U won't stay on


PD1-PNL 12V
PD2-PNL 12V
PD3-GRD
PD4-GRD
PD5-UR13.2V
PD6-UR13.2V
PD7-UR13.2V No wire to main board
PD8-UR13.2V No wire to main board
PD9-GRD
PD10-GRD
PD11-GRD No wire to main board
PD12-GRD No wire to main board
PD13-AC_DET
PD14-PS_ON
PD15-BU5V
PD16-PNL_POW
PD17-PWM1
PD18-NC
PD19-NC
PD20-NC
PD21-OFL No connection to main board
PD22-ERROR
PD23-PWM2 No connection to main board
PD24-STB

[budm]

Re: Sharp LC-60LE600U won't stay on

Man! you cannot that type in all those pin name for us, too much to ask? Nice upside down picture by the way.

[dpolk]

Re: Sharp LC-60LE600U won't stay on

Sorry about that. I fixed the last post.

[dpolk]

Re: Sharp LC-60LE600U won't stay on

Update: This website is a wealth of knowledge. Thank you all of the help you give. I have been reading and testing trying to figure this thing out. I found two diodes that tested funny in the board. D7950 and D7901. When I pulled them out of the board I think they tested fine. D7950 - Open one way and .325 the other. D7901 - Open one way and .771 the other way.

I'm not quite sure how to test the three pin diodes. I tested D7130 and D7131 in the board. Both tested identical in diode mode on the DMM. From the center pin (2) to pin (1), tested .164 one way and .693 the other way. It tests identical from pin 2 to pin 3.

Also another bit of information, the front led doesn't show any codes...actually it never turns on.

Any ideas on what to test next?

[dpolk]

Re: Sharp LC-60LE600U won't stay on

Made some good headway tonight. I unplugged the plug for the LED backlights and restarted the TV with the Input and Vol-. I was able to keep the TV from shutting down after 15 secs like before. I was able to input a source and see the image using a flashlight.

I'm encouraged, but still not sure where to go from here. Any ideas?

[budm]

Re: Sharp LC-60LE600U won't stay on

Can we see the pictures of the whole back side of the TV so we can see how all the boards are connected together?

[dpolk]

Re: Sharp LC-60LE600U won't stay on

Thanks for helping budm! Attached is the back with the three boards connected. Also attached is a closer pic of the board where the led plug is located.

[dpolk]

Re: Sharp LC-60LE600U won't stay on

With the led backlight plug removed, and the TV running, I am measuring 147 Vdc out of each of the 4 led outputs. I am assuming one of the led's is shorted in a led strip. Is there a way to test the led strips while still in the TV?

If not, can someone head me in the right direction to disassembly to access the strips to test each led?

[budm]

Re: Sharp LC-60LE600U won't stay on

The 147V is the no load Voltage of the LED power supply that supplies top the Anode of the LED string.
Lets try this first: we need to see if there is bad LED wiring that is has low resistance to GND or not first.
1) TV not plugged in, put the LED connector back in place, thenput meter in Ohm mode. 2) Put black probe on the chassis, then use the read probe to check the resistance of each pin of the LED connector to see if any of them show low resistance, make sure to report if the resistance is in Ohm, K Ohm , or M Ohm.
You can also buy LED tester to check each string of the LED, it looks like you have 4 strings of LEDs..

[dpolk]

Re: Sharp LC-60LE600U won't stay on

Pin 1 = 98.4 K Ohm
Pin 3 = OL
Pin 5 = 98.3 K Ohm
Pin 7 = OL
Pin 9 = 66.8 K Ohm
Pin 11 = OL
Pin 13 = 67.2 K Ohm
Pin 15 = OL
Pin 2,4,6,8,10,12,14 = NC

[budm]

Re: Sharp LC-60LE600U won't stay on

OK, next test is to leave black probe on the chassis then put red probe on pin 1 then turn on the TV and see how high the DCV goes up too and wait a couple seconds to see how low it drops down to, then turn off the TV and move the red probe to pin 3 and repeat the test, do that again on pin 5, 7, 9, 11, 13, 15.
This test may tell us if you have one or more of bad LED strings.

[dpolk]

Re: Sharp LC-60LE600U won't stay on

I will try this again tomorrow, but I did this earlier and the led's shut off so quickly that my DMM could not read it fast enough. I may have to take it to work and have the EE's put a scope on it.

Thanks again for your help!

[budm]

Re: Sharp LC-60LE600U won't stay on

That's OK, we are just looking for comparative reading of each LED strings to tell us if one of them is off value or not.

[dpolk]

Re: Sharp LC-60LE600U won't stay on

Pin 1 = 81.5 Vdc at power, begins dropping at BL on, drops to 0
Pin 5 = 77.2 Vdc at power, begins dropping at BL on, drops to 0
Pin 9 = 76.4 Vdc at power, jumps to 125-140 Vdc at BL on, then drop to 0.
Pin 13 = 82.2 Vdc at power, begins dropping at BL on, drops to 0

[budm]

Re: Sharp LC-60LE600U won't stay on

Where are the Voltages for pin 3, 7, 11, 15 which are the Cathode return for the LED strings?
"Pin 9 = 76.4 Vdc at power, jumps to 125-140 Vdc at BL on, then drop to 0."
So far it looks like the LED string #3 has the problem.

[dpolk]

Re: Sharp LC-60LE600U won't stay on

Sorry, made an assumption I that was incorrect. I will measure those tonight.

[dpolk]

Re: Sharp LC-60LE600U won't stay on

Well I began tearing into the TV before I realized budm had asked what the - voltages were on the led stings.

I did test all LED's and they all light up. I used 2 batteries totaling 5.2v with a 120 ohm resistor. Not really sure where to go from here.

[dskall]

Re: Sharp LC-60LE600U won't stay on

Well if you have panel off you can connect main and power board without panel connected and try switching on. The backlights should flash on and you can make sure they all work. Testing individually is not a reliable test.