SHARP LC46E77UN just power light on

[kgavionics]

Hi
i have a non working SHARP LC46E77UN.when plugged to the power the power light turns on then i hear relay clicking sound, the tv stays black non back-light and after a minute or so, the OPC and Power light blink together 1 time, then The power light blinks 2 more time and the cycle repeats.
i downloaded the service manual (page 61) and its says if the power light blinks 3 times,then there's a bad communication with the main CPU.
i took the TV apart and i forced the TV to start ( vol+ and channel down and plugging the power cable in same time) and measured the voltages on the power board (model : RDENCA336WJQZ),all the voltages were ok expect the PLN 12V(the connector in left had side ( goes to the tcon board).
I also took the power supply board out and verified all the MOSFET, diodes and resistors and i didn't found any suspicious components.i also check the ESR of some caps and they are ok.
so to summarize, the blinking code says there's a problem with the main board and the logic says there's something wrong with the power supply ( there no voltage at all that goes to the Tcon board)
i have uploaded the tv service manual.can someone help me to fix the problem.

[kgavionics]

Re: SHARP LC46E77UN just power light on

update:
i checked the main board with an my oscilloscope and the problem, i didn't find any signal or whatsoever even though, the voltages are present in the connector of the MB.There's no signal from the main board to the Tcon board either.

[budm]

Re: SHARP LC46E77UN just power light on

So what is Voltage you are getting at the PLN12V?
0V? 1V? 2V?...........

[dskall]

Re: SHARP LC46E77UN just power light on

Need some pictures of all boards and back of tv

[kgavionics]

Re: SHARP LC46E77UN just power light on

So what is Voltage you are getting at the PLN12V?
0V? 1V? 2V?...........

i'm getting 0v in all circumstances

I'm looking for the power supply manual on internet,but i can't find it.if someone has it, that would be great.it gonna help me a lot.

[budm]

Re: SHARP LC46E77UN just power light on

At this point we need the DCV readings of all the pins of the power supply connector that goes back to the main board so we can see what you really have on those pins.
Please make sure to report the readings in this format, for examples:
BL-ON: TV OFF = XX V, TV ON (POWER SWITCH is activated) = xx V
5VSTBY: ..............

[kgavionics]

Re: SHARP LC46E77UN just power light on

Hi once again
THere's 2 connectors that goes from the PSB to the mainboard and 1 connector thtat goes from the PSB to the TCON board.
here's a summary of all the voltages i measured:

main connector 12 pins, but only 7 pins connected:
Tv ON:
1-13.5signal=13.1v
2-13.5signal=13.1v
3-NC
4-NC
5-SIGNAL AUDIO=0V
6-SIGNAL AUDIO=0V
7-NC
8-NC
9-AC_DET=3V
10-PSON=2.86V
11-BU5V=4.98V
PNL_POW=0V
Tv off:
1-13.5signal=0v
2-13.5signal=0v
3-NC
4-NC
5-SIGNAL AUDIO=0V
6-SIGNAL AUDIO=0V
7-NC
8-NC
9-AC_DET=3V
10-PSON=0V
11-BU5V=4.98V
PNL_POW=0V

There's another 6 pins connectors that goes from PSB to mainboard market INV1 to INV6.When the tv is off all of them are 0v and when tv is ON all the pins are 0V expect INV6 is 3v.

The 4 pins connectors that goes from the PSB to the TCON board:
TV OFF:
1-PNL12V=0V
2-1-PNL12V=0V
3-GND=0V
4-GND=0V

TV ON:
1-PNL12V=0.40V
2-1-PNL12V=0.40V
3-GND=0V
4-GND=0V

I don't have the PSB schematics, but a traced down the PNL12 it coming from a 4 pins SHARP voltage regulator part number pq30rv31 i was lucky enough to find a couple of them in my storage box.i replaced it, but no luck i still have the same problem.

[dskall]

Re: SHARP LC46E77UN just power light on

Appears your problem is with main board

[kgavionics]

Re: SHARP LC46E77UN just power light on

Appears your problem is with main board

i want to believe it, but the lack on power on the tcon board ( PLN12) keeps me thinking that the power supply is not working as it should be.
how can i be sure that the PSB is good and the problem is coming from the mainboard?
The thing that pisses me off,that i checked all almost all the components on the PSB and they seems to be good.

[budm]

Re: SHARP LC46E77UN just power light on

'PNL_POW=0V'

The main board is not sending the 'PNL_POW' control signal to turn on the 12V REGULTOR/SWITCH IC7121 on the power supply board to provide the 12VDC to run the T-CON board.
The 'PNL_POW' should goes to >2VDC and stay at that level when the TV is power ON.

Sharp RDENCA336WJQZ (DPS-286AP, DPS-286AP A) Power Supply Unit
http://www.shopjimmy.com/sharp-rdenc...pply-unit.htm#
Pictures provided by shojimmy.

[kgavionics]

Re: SHARP LC46E77UN just power light on

'PNL_POW=0V'

The main board is not sending the 'PNL_POW' control signal to turn on the 12V REGULTOR/SWITCH IC7121 on the power supply board to provide the 12VDC to run the T-CON board.
The 'PNL_POW' should goes to >2VDC and stay at that level when the TV is power ON.

Sharp RDENCA336WJQZ (DPS-286AP, DPS-286AP A) Power Supply Unit
http://www.shopjimmy.com/sharp-rdenc...pply-unit.htm#
Pictures provided by shojimmy.

Thanks budm for the heads up.so, you think the problem is main board?

[dskall]

Re: SHARP LC46E77UN just power light on

Ya well you confirmed it with your voltage readings

[budm]

Re: SHARP LC46E77UN just power light on

Please make sure that the PNL_POW really shows 0V because most the time the IC7121 fails to switch on, you should verify that you really do not have control Voltage at the control pin of the IC7121 for sure.

[kgavionics]

Re: SHARP LC46E77UN just power light on

Please make sure that the PNL_POW really shows 0V because most the time the IC7121 fails to switch on, you should verify that you really do not have control Voltage at the control pin of the IC7121 for sure.

the voltage i have on IC7121 :
pin1(VIN)=13V
pin2(VOUT)=0.4v
Pin3(GROUND)=0v
PIN4(CONTROL VOLTAGE)=4V

[budm]

Re: SHARP LC46E77UN just power light on

Does that PIN4 Voltage change state when you turn the TV on and off/ What is the IC P/N?

[kgavionics]

Re: SHARP LC46E77UN just power light on

Does that PIN4 Voltage change state when you turn the TV on and off/ What is the IC P/N?

The pin4 changes state from 0 to 4V when turning the tv ON and back to 0v when turning it off.
the part number of the circuit is PQ30RV31
i have attached it's datasheet bellow.

[budm]

Re: SHARP LC46E77UN just power light on

That means you had error measurement of the PNL_PWR PIN because the IC control pin is toggling, it cannot be at steady 0V as your report shows.
Next thing is to find out if the Output pin is seeing very low resistance or not, so check the resistance between the output pin and GND and report the reading, if the reading shows 1000's of Ohms then the IC is bad since it is getting the signal for it to come on.
That IC is the commonly failed IC BTW.

[kgavionics]

Re: SHARP LC46E77UN just power light on

thanks budm for you help, i really appreciate it.
i measured 782 ohm between output pin and ground, so this mean that the circuit is bad.i'm gonna replace it and report back.

[kgavionics]

Re: SHARP LC46E77UN just power light on

update:
Replaced a brand new regulator and still no luck.the same thing, the voltages are:
pin1(VIN)=13V
pin2(VOUT)=0.35v
Pin3(GROUND)=0v
PIN4(CONTROL VOLTAGE)=4V
this problem is getting me crazy...

[budm]

Re: SHARP LC46E77UN just power light on

remove that connector that goes to the tcon to see if the 12v will come up.
I expect it to be over 1000 Ohms.