SHARP LC46E77UN just power light on

[budm]

Re: SHARP LC46E77UN just power light on

BTW, I just look at the spec of the IC you provided, high = OUTPUT OFF.
Are you sure that is the correct P/N? It is not KIA78R12XXX?

[kgavionics]

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.

unfortunately, no still have 0.4V.

[kgavionics]

Re: SHARP LC46E77UN just power light on

BTW, I just look at the spec of the IC you provided, high = OUTPUT OFF.

yes i noticed that in datasheet, but i don't get it, in my case when the set is on, the control pin is high and vice versa.weird..

[budm]

Re: SHARP LC46E77UN just power light on

Switch q7123 and the diode D7127 (ANODE is connected to the Collector of q7123) are the one that provide the 4V to turn off the IC, so you should be able to force the Anode side of D7127 to go low to turn on the IC.

[kgavionics]

Re: SHARP LC46E77UN just power light on

Switch q7123 and the diode D7127 (ANODE is connected to the Collector of q7123) are the one that provide the 4V to turn off the IC, so you should be able to force the Anode side of D7127 to go low to turn on the IC.

sorry i didn't get your point!!what do you mean by switch the transistor and the diode?

[budm]

Re: SHARP LC46E77UN just power light on

if you look the application of the diagram regarding to turning it on and off using pin 4, you can see the diode connected to pin 4 of the IC in the diagram and also in your board, the transistor on your board provides that 4V which is higher that the Vref of 1.25V to turn off the IC.
Right now something is not making sense due to the fact that Pin 4 goes high when TV is on, and 0V when the TV is OFF.
BTW, are you able to verify that PNL_PWR control pin is actually changing state?
If it is still sitting at 0V then you may be able to force that line high using pull-up resistor, but the PNL_PWR wire going back to the main board has to be disconnected first.

[kgavionics]

Re: SHARP LC46E77UN just power light on

i did another set of measurement and PNL_POW is always 0V in all circumstances.i'm thinking adding a pull-up resistor from another pin like PS_ON , but if i disconnect the connector i loose all the another signals.do you have an idea how can i do it?

[budm]

Re: SHARP LC46E77UN just power light on

You have to disconnect just that PNL_PWR wire from the connector. The resistor will be be 470~1K resistor between BU5V and the PNL_PWR pin, that way if every thing else are OK then you should get the TV to function in test mode then you can find out later why the PNL_PWR is stuck low.
BTW, did you check the resistance between the PNL_PWR and GND to see what you have?

[kgavionics]

Re: SHARP LC46E77UN just power light on

You have to disconnect just that PNL_PWR wire from the connector. The resistor will be be 470~1K resistor between BU5V and the PNL_PWR pin, that way if every thing else are OK then you should get the TV to function in test mode then you can find out later why the PNL_PWR is stuck low.
BTW, did you check the resistance between the PNL_PWR and GND to see what you have?

the resistance between PNL_PWR and GND is 23.39 Kohm.
regarding the pull up resistor i'll do it right away.
thanks

[budm]

Re: SHARP LC46E77UN just power light on

Hope fully every thing will work with this test if there is no other problem with the main board, then we can use other command pin to turn on the PNL12V circuit instead.

[kgavionics]

Re: SHARP LC46E77UN just power light on

Hope fully every thing will work with this test if there is no other problem with the main board, then we can use other command pin to turn on the PNL12V circuit instead.

No, unfortunately. i disconnected the PNL_POW and put the pull up resistor, fire up the tv and still hear the relay clicking no picture no back light.i forced the tv to power up ( vol+, channel- while plugging the power cord) i had the same result black picture and no backlight, but i had the 12V to the TCON board, so the power supply seems to work ok.
the only thing that bugs me if i have problem with the main board why i dont have a back-light? this is by far the most complicated repair that i came across.
i saw a thread on this forum, a guy had a similar problem like mine and turned out the the microprocessor heat sink was grounding out some other components, but checked mine and it seems far from the components underneath.
i don't know what i'm gonna do in the next step.

[budm]

Re: SHARP LC46E77UN just power light on

I do not see the reading of the BL-ON and the Dimming control signal in your reports.

[kgavionics]

Re: SHARP LC46E77UN just power light on

I do not see the reading of the BL-ON and the Dimming control signal in your reports.

i don't have any BL-ON signal on the connector
here's a picture of the left hand side of the PSB:
the first connector marked INV1 to INV6 ( Pin1 to Pin5 the pins are 0V whatever the tv is on or off).Pin6 is 0v when tv is off and goes to 3V when tv is on.
the second connector voltages are listed in my older post.
the third connector is PLN 12V with the pull up resistor is giving power to the tcon board.
i have attached a close up picture of the connectors

[dick_barton]

Re: SHARP LC46E77UN just power light on

You give the connector readings including BL_ON in your post #7

[kgavionics]

Re: SHARP LC46E77UN just power light on

You give the connector readings including BL_ON in your post #7

No i haven't given BL_ON, it was BU5V.

[kgavionics]

Re: SHARP LC46E77UN just power light on

update:
i received my Mesr-100 v2 in circuit esr meter today, i checked one of the 3 electrolytic capacitors on mainboard.The capacitor value is 470uF @25V, the esr should not exceed 0.12ohm and i found 0.7 ohm which indicates that this capacitor is bad.i'll try to find this cap in my storage box and replace and see if it resolves the problem.

[budm]

Re: SHARP LC46E77UN just power light on

Is that the reading with the cap is on the board or off the board? How about its capacitance?

[kgavionics]

Re: SHARP LC46E77UN just power light on

Is that the reading with the cap is on the board or off the board? How about its capacitance?

the cap was good, because i was measuring it without zeroing the meter.in addition, i took a look to the manual and turned out that this cap is hooked up to the audio amplifier, so even the cap is bad,the set would turn on.
i'll keep on investigating the problem, because i can't find any replacement board in the internet.

[budm]

Re: SHARP LC46E77UN just power light on

OK, I thought you have already used that ZERO button to ZERO out the test leads.

[kgavionics]

Re: SHARP LC46E77UN just power light on

i did a little bit of troubleshooting this evening and found something interesting.
see attached image.
there's some thing wrong with the resistor R9630,it's 1ohm resistor and it's taking 4.2v of voltage drop.i measured it's resistance and i found 140kohm.the other resistor is measuring 1ohm as expected.clearly,there's a problem with it.now need to find a resistor and replace it.
to be continued...