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**Gjackson** · 08-26-2021, 08:56 AM

Re: SHARP LC-70LE735X will not turn on

So,

to begin with I'm definitely not an expert but.. It seems as if the PSU is working fine and the Tv powers on right? You mentioned that the backlights flash on startup and then immediately go off, I fixed a TV in the past that had the exact same symptom.. It was caused by a faulty MOSFET that was used to power on the backlight so I would suggest that you replace the FET's that run the backlight to start with. On my PSU I had 2 FET's that ran the backlight, I desoldered them and tested both and found that one of them was shorted. On your PSU I think that the 2 FET's are Q7700 and Q7701 at the middle top of the board.

That should fix the backlight issue but if the TV isn't behaving correctly and the PSU is pumping out correct voltages then it might be a main board fault.

Good luck!

**bl0wfish** · 08-26-2021, 05:06 PM

Re: SHARP LC-70LE735X will not turn on

Originally posted by Gjackson View Post

So,

to begin with I'm definitely not an expert but.. It seems as if the PSU is working fine and the Tv powers on right? You mentioned that the backlights flash on startup and then immediately go off, I fixed a TV in the past that had the exact same symptom.. It was caused by a faulty MOSFET that was used to power on the backlight so I would suggest that you replace the FET's that run the backlight to start with. On my PSU I had 2 FET's that ran the backlight, I desoldered them and tested both and found that one of them was shorted. On your PSU I think that the 2 FET's are Q7700 and Q7701 at the middle top of the board.

That should fix the backlight issue but if the TV isn't behaving correctly and the PSU is pumping out correct voltages then it might be a main board fault.

Good luck!

Hey mate,

Yes and no.
i can only get the leds to flash if i force on the display with the mainboard disconnected.
otherwise tv hooked up as normal i only get 5v to PD Pin 15 BU5V

what you say makes sense. so i will check those fets. im real crap at checking with a multimeter, so ill use my tester haha.
i will have a coffee and check them and report back today. pain in arse. all locked in by heatsinks lol

thanks heaps
Ash

**budwich** · 08-27-2021, 04:09 AM

Re: SHARP LC-70LE735X will not turn on

you never posted what voltages you get on pins 21 and 22 with the main board. Further, there is a "force sequence" to allow the set to start using the "plug in and holding vol up or down" search for more on this. Does that work?

**bl0wfish** · 08-27-2021, 06:03 AM

Re: SHARP LC-70LE735X will not turn on

Originally posted by Gjackson View Post

Q7700 and Q7701 at the middle top of the board.

Checked those with my tester. Came up good as far as I understand fets. I also lifted some traces and checked around the fets. Attached below is my findings. Everything seemed in spec

Attached Files

**bl0wfish** · 08-27-2021, 06:08 AM

Re: SHARP LC-70LE735X will not turn on

Originally posted by budwich View Post

you never posted what voltages you get on pins 21 and 22 with the main board. Further, there is a "force sequence" to allow the set to start using the "plug in and holding vol up or down" search for more on this. Does that work?

Oh I had a blonde moment and missed those. Here they are.
But looks like I forgot 22. Originally I missed 19 and 21
See below. Ill check again tomorrow. Sorry

Code:

PIN	LABEL		VOLTAGE
1	PNL 12v		+12v
2	PNL 12v		+12v
3	
4	
5	UR 13.2v	+13v
6	UR 13.2v	+13v
7	UR 13.2v	+13v
8 
9	
10	
11	
12	
13	AC-DET		+3.3v
14	PS ON		+5v
15	BU 5v		+5v
16	PNL-POW		+5v
17	
18	
19	DIMMER		+4.6v (edited)
20	
21	OFL		+4.2v (edited)
22	ERROR	
23	
24	STB		+5v

Sorry. Again I never checked voltages with main board plugged in. So I will do that again tomorrow plugged in. But the vol + / - never worked as I tried that first. Furtherest ive got was 5v to the 5 pins on PD, which resulted in the display to flash and shut down. Isolated from main board

**budwich** · 08-27-2021, 07:30 AM

Re: SHARP LC-70LE735X will not turn on

there isn't always success with the "force on" sequence. It is important to know the exact sequence / steps that you are following for the sequence AND the state of the tv (what lights are present to indicate the state) when it is attempted.

**bl0wfish** · 08-27-2021, 11:48 PM

Re: SHARP LC-70LE735X will not turn on

Ok how would you suggest i do the sequence? What i did was have main board disconnected.
A lead from pd pin15 to breadboard. Then 5x 1k resistors to each pin. Which is pin 14 16 19 21 24. This gave me the flash and shut down of led.

The leds peaked around 200+v. But as I said its to fast to catch anything accurately. If I just run a 1k from bu5v to pson I get PFC boost to 400v. Both methods did this. The only time the standby led is flashing. Is with everything plugged in as normal. But is off when you press power.

Vol + - does nothing. I tried swapping diodes at d7951, no change. And the 3 optocouplers below it. No change. There is a hairline frack on a transformer. I believe on the led driver circuit. I.cant find datasheets for any of them. I dont know how to test these. I assume they need to be in spec ot resistance. *shrugs*.

This tv is testing my patience. Every tv I've repaired with backlight fault hasn't had a protection circuit. My led tester is consistent on all led strings. If one was bad. We would see. I will check them again in dark and see if I can spot a dud led.

Can I force this tv to run with backlight off and see where it takes me?.
I dont want to buy a new board. My goal was components and donate to the forum as money well spent

**bl0wfish** · 08-28-2021, 07:25 AM

Re: SHARP LC-70LE735X will not turn on

Ok, so i started again in aid to hopefully get some more input on what the issue is with the TV.
With the TV all hooked up as normal with power on and in standby (i assume - as power LED flashes RED slowly)

i get the following voltages with a chassis, board ground

Code:

5v on BU5V only.
5.5v on D7951 cathode, 0v anode.

The following caps on pos and neg legs

Code:

C7800 ABC 325v
C7951 5.5v
C7121 0v
C7955 5v
C7728 0v
C7138 0v
C7133 14.9v

----
Turning on Power with Power Button on side of TV turns off the RED POWER LED at front.
this is still with everything connected as normal.

i get the following voltages with a chassis, board ground

Code:

5v on BU5V only.
5.5v on D7951 cathode, 0v anode.

The following caps on pos and neg legs

Code:

C7800 ABC 325v
C7951 5.5v
C7121 0v
C7955 5v
C7728 0v
C7138 0v
C7133 13.1v

----

Now the following is with Mainboard disconnected
Forced POWERUP
BU5V via 1k to PS_ON
i get the following voltages with a chassis, board ground on
PD Connector
only posting pins that had a voltage present

Code:

PIN 5,6,7,8 - UR 13.2 = 13.07v
PIN 13 - AC-DET = 3.298v
PIN 14 - PS_ON = 4.99v
PIN 15 - BU5V = 4.99v
PIN 16 - PNL-POW = 0.113

The following caps on pos and neg legs

Code:

C7800 ABC 405v
C7951 5.67v
C7121 0v
C7955 4.99v
C7728 12.53v
C7138 13.07v
C7133 13.07v

----

Lastly i found i had some feedback with AC Disconnected.
Holding In VOL-.VOL+,POWER and then switching on AC Source.

Power LED Comes on and FLASHES Yellow or Green (hard to make out) for X amount of seconds, BACKLIGHTS FLASH ON THEN OFF INSTANTLY, then LED disappears, OFC LED Illuminates Yellow or Green and turns off. (videos attached below)

During this i watched the Voltages Boost from 325v to 405v on PFC
Caps C7800ABC.

I will attach the two videos of POWER LED situation.

links to youtube of power LED
Standby - https://www.youtube.com/watch?v=lTiANmN8A4w
VOL Reset test in Dark (description above) - https://www.youtube.com/watch?v=0msTmGOk10c
VOL Reset test (description above) - https://www.youtube.com/watch?v=YLCjLDZg7Hg

Thankyou and i cross my fingers we can get this working. i dont want to bin a 70"

Ashley

**budwich** · 08-28-2021, 08:24 AM

Re: SHARP LC-70LE735X will not turn on

On my limited reads, a force on should allow the set to "light up" for a while IF the lights are operationally OK. Based on reads, a led tester isn't able to drive the leds with enough current to cause a "fault" condition to appear in some cases. Hopefully, some else will provide further guidance / suggestions.

**bl0wfish** · 08-28-2021, 08:32 AM

Re: SHARP LC-70LE735X will not turn on

Originally posted by budwich View Post

On my limited reads, a force on should allow the set to "light up" for a while IF the lights are operationally OK. Based on reads, a led tester isn't able to drive the leds with enough current to cause a "fault" condition to appear in some cases. Hopefully, some else will provide further guidance / suggestions.

Arghhh, i see. i am not technically clever enough. but is there a way to bypass the led strips so i can power on the unit? then i can simply use a torch and see if the unit is doing anything?
this is what i used to test them whilst still under the panel
https://www.shopjimmy.com/sid-gj2c-l...n=sid-gj2c-led

Thanks for your time mate.
Ash

**budwich** · 08-28-2021, 03:48 PM

Re: SHARP LC-70LE735X will not turn on

:-( One question, now that you appear to have some form of force on. have you checked pin 22 during these attempts to see what the reading is? The other thing that you can try during the "force on tests" is to have one of the cables from the tcon to panel disconnected. See if that changes anything. Repeat the test, disconnecting one cable only at a time. Possibly this might help IF there is some sort of panel issue happening that is causing some "mis fire" of the monitor system. I am still thinking your tests seem to point at a bad led somewhere. My personal experience with a sharp 70 was a bad panel (driver) and force on's did work.... but the set was an older "vintage" so perhaps they "improved" the protection system to prevent further failures of any circuitry when a fault is detected.

one other thing, you mention the "PFC boost" but have you monitored the voltage going to one of the strings? That might tell you more about what's happening as the leds flash on. You should see some form of "max" string voltage and then perhaps it decaying (fast) with shutdown.... your eyes / meter will be better than my guess.

**RDC55** · 08-28-2021, 06:27 PM

Re: SHARP LC-70LE735X will not turn on

Some downloads from ElectroTanya that may help

Adding a complete picture of the back of the TV with interconnect might also be helpful.

Attached Files

**bl0wfish** · 08-28-2021, 06:43 PM

Re: SHARP LC-70LE735X will not turn on

Originally posted by budwich View Post

:-( One question, now that you appear to have some form of force on. have you checked pin 22 during these attempts to see what the reading is?

yes my last post i checked all pins. if no voltage was present. it wasnt posted.
i can do the force on again and triple check. just to confirm.
1k resistor each from BU5V to PS_ON, PNL_POW, DIMMER, OFL, STB ?

Originally posted by budwich View Post

one other thing, you mention the "PFC boost" but have you monitored the voltage going to one of the strings? That might tell you more about what's happening as the leds flash on. You should see some form of "max" string voltage and then perhaps it decaying (fast) with shutdown.... your eyes / meter will be better than my guess.

Yes i did try and catch the LED Voltages as they spiked, mentioned in post #1

Originally posted by bl0wfish View Post

I tried catching the voltage on the led strips. Its hard to say being so fast. I seen between 112v to 200+v. But thats not solid. Its just to quick to be accurate. The max hold on my dmm was only catching 40v.

then again in post #8

Originally posted by bl0wfish View Post

The leds peaked around 200+v. But as I said its to fast to catch anything accurately. If I just run a 1k from bu5v to pson I get PFC boost to 400v. Both methods did this. The only time the standby led is flashing. Is with everything plugged in as normal. But is off when you press power.

without an analogue meter its too hard to catch.
but i will persist and keep doing it and see what i get. we cant go off those figures as its so fast it is highly innaccurate. the max hold only catches bugger all. and i am now going to do these tests with TCON disconnected one Flex at a time and report my findings soon. Thankyou.
ASH

**bl0wfish** · 08-28-2021, 07:28 PM

Re: SHARP LC-70LE735X will not turn on

Originally posted by RDC55 View Post

Some downloads from ElectroTanya that may help

Adding a complete picture of the back of the TV with interconnect might also be helpful.

yes i have all those files (i think) well at least the PSU SCH and PHOTOS, but not all of it makes sense to me. thats why i am here. yes i will get a photo of the back of unit with everything in place.

thanks guys for all the replies. i am so thankful

**bl0wfish** · 08-29-2021, 05:56 AM

Re: SHARP LC-70LE735X will not turn on

Originally posted by budwich View Post

:-( One question, now that you appear to have some form of force on. have you checked pin 22 during these attempts to see what the reading is? The other thing that you can try during the "force on tests" is to have one of the cables from the tcon to panel disconnected. See if that changes anything. Repeat the test, disconnecting one cable only at a time.

ok good sir, i did those tests.
Its way to hard capturing Backlight voltages :-(
so with power disconnected at AC and probing voltages on PIN22 ERROR
and the backlights.

i got the following with reset/force on via VOL- and INPUT whilst connecting AC (this is for all the below tests)
----
Both TCON 7001 and 7002 ribbon connected.
i get

Code:

3.22v on PIN22 ERROR PFC hits 405v, LED strips hit around 150~v

power light goes green. led strips flash, green power led goes off, then power led turns red and unit switches off.
----
TCON 7001 Disconnected only (left i assume) - see video https://www.youtube.com/watch?v=PFgYl9pAJuA

Code:

3.28v PIN22 ERROR, 405v PFC, 150~v Backlight

----
TCON 7002 Disconnected only (right i assume) - see video https://www.youtube.com/watch?v=lHBwYx0TcG0

Code:

3.28v PIN22 ERROR, 405v PFC, 150~v Backlight

----
Both TCON Disconnected.

Code:

3.28v PIN22 ERROR, 405v PFC, 150~v Backlight

Pretty much same result as having both TCON Connected.
----
i searched and read deep into this forum and found this post by BUDM,
https://www.badcaps.net/forum/showpo...6&postcount=24
sounds like he is confirming a higher voltage on ERROR PIN22 is Normal.
1v and under is an error i believe?

sounds more and more like LED, but my tester pulls 160v on every string. thats not solid to say they are ok, its just weird its consistent. if a string was out. you would expect to see under 160v. the videos. im not expert. this is why i am here. any other tests i have missed guys?
videos give me hope that mainboard and power supply are good until backlight circuit and led's. is my tcon ok?

And here's the rear of TV as requested.

thanks heaps

Attached Files

**budwich** · 08-29-2021, 06:11 AM

Re: SHARP LC-70LE735X will not turn on

well that's seems to be some what different that you were reporting earlier in terms of pin 22 which you indicated was 0 (I think). Further, I can see an image on the screen during your "tcon disconnect" at around 18 second mark on the right side and at about the 15 second mark on the other video. IF you actually feed in a full screen picture, it is likely that you would see "half a full screen"... for a brief second.

As you indicate, it is possible that some sets indicate errors as "low" while others indicate "high". My limited experience with the sharp... my reads are that it is normally high for an error condition. Either way, it looks more likely to be a led issue.

**bl0wfish** · 08-29-2021, 06:23 AM

Re: SHARP LC-70LE735X will not turn on

Originally posted by budwich View Post

well that's seems to be some what different that you were reporting earlier in terms of pin 22 which you indicated was 0 (I think). Further, I can see an image on the screen during your "tcon disconnect" at around 18 second mark on the right side and at about the 15 second mark on the other video. IF you actually feed in a full screen picture, it is likely that you would see "half a full screen"... for a brief second.

As you indicate, it is possible that some sets indicate errors as "low" while others indicate "high". My limited experience with the sharp... my reads are that it is normally high for an error condition. Either way, it looks more likely to be a led issue.

i wouldnt have a clue with high and low voltages being error or not. i only shared BUDM post confirming High is good and Low is bad for another Sharp TV. yes i seen the screen display also. and yes i was getting 0v previously. was doing something wrong obviously. i did do the power on test different this time tho. im happy to swap led. and im confident in removing panel. done it alot of times. but i want to be sure. i wish it was simple and disable backlight or have it off so i could test the tv with torch method. i wouldnt have gotten this far without you guys. i shall donate some money tomorrow

**bl0wfish** · 09-05-2021, 07:31 AM

Re: SHARP LC-70LE735X will not turn on

Hey guys. Had this sitting off bench since last post. Been fixing a few other things around house. Before I proceed with removing lcd panel. I want to be certain its led diodes in the backlight strips.

Im using a good led tester. There's a large amount of strings behind this 70" panel and im consistently pulling 160v on each string. If we had some leds out. Wouldnt I notice this on front of screen in dark? And I'd have a noticeable difference in voltage on my tester?

This tester has always worked great in finding a faulty led diode. Its very picky. Perhaps I make a video or photos of the tests.

Yes the main driver caps boost to 405v and then taper back down and the leds hit 160v and drops down after force on or vol reset trick. Yes I know 160v is low. But this is each string. Its got a shitload inside split into about 14 strings. What I wanna know is how can I be certain its NOT the led driver and after led are swapped for new and I dont do the reset. Will it continue to shut down?

In the meantime im going to source the leds
Havent found any yet. Ill try searching by lcd sticker on unit tomorrow

Never worked on a sharp before. Im not trying to avoid swapping led strips. I just want to be certain. Can we summon the almighty gods around here.

Thanks for your time

(Edit) soon as I find the leds. Ill work out how many mA they should draw per string and see what my tester does. I understand it tester only doing 50 or 60mA its not enough to get true diagnosis

**bl0wfish** · 09-11-2021, 03:58 AM

Re: SHARP LC-70LE735X will not turn on

me again guys. im close to having to take the panel off and check each backlight led. i couldnt find any backlights for my tv. my tester does 150ma. checked it with multimeter.
once i have a fully working 100% backlight. i will need to do a VOL INPUT reset to clear errors? never worked on a sharp. every time ive done a backlight, tv still works

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