Sharp Aquos 40aj6ke backlight ok, no sound or video

[Questcom]

Hi All,

I have recently purchased a faulty Sharp Aquos 40aj6ke which turns on and has backlight but has no sound or video, the person I brought it from told me he had changed the main board and the same fault was there.

I have tested voltages on main board and they seems ok, the backlight is at 75v, I believe this tv has 3 x 8 strips of leds which 75v would work out to around 3v per led

I think the issue is on the board that attaches to the lcd, doing a bit of digging watching videos etc, there is a lot of mention of vgl and vgh being around -8 and 35v, but I cannot find them

testing voltages on that board I only found 1v, 1.8v, 3.3v and 12v

I've added photos of the boards, if anyone could shed some light where vgl and vgh should be that would be great

any help would be appreciated

thank you

peter

[Questcom]

Re: Sharp Aquos 40aj6ke backlight ok, no sound or video

ok I found them

voffe and vone both at 0v

done diode test no shorts found

any suggestions

[Questcom]

Re: Sharp Aquos 40aj6ke backlight ok, no sound or video

can anyone give me any ideas please, I got another panel board through today, but it would mean removing them orange ribbon cables and soldering them to the new one, but I just feel that a bit drastic at this time, lol

has anyone has datasheets on rt6935 and rt6939?

[dick_barton]

Re: Sharp Aquos 40aj6ke backlight ok, no sound or video

What orange ribbon cables? if you are referring to the ones from the LCD panel to the panel circuit board then you need a special machine to do that job which is well out of the price range of any servicing shop.

[Questcom]

Re: Sharp Aquos 40aj6ke backlight ok, no sound or video

What orange ribbon cables? if you are referring to the ones from the LCD panel to the panel circuit board then you need a special machine to do that job which is well out of the price range of any servicing shop.

Thanks for your reply, yes I was referring to the ones from LCD panel to panel PCB, is there any reason why these cannot be soldered on instead?

[jimbofz]

Re: Sharp Aquos 40aj6ke backlight ok, no sound or video

hi just seen this post ,i had exactly same problem some months ago
i posted it on here .
i tried to find data on those two ics (dc to dc converters ) impossible!
i had no shorts on any of the supplies on the boards ,its still waiting until i can do a comparison with another .so good luck .
remove the plastic bezel to expose the foils ,use a magnifying glass and look for any evidence of spillage ,its common for screen cleaning with spray ,allowing it to run down between bezel and panel .sometimes you can be lucky and clean the area
but more often it results in panel damage.

[Questcom]

Re: Sharp Aquos 40aj6ke backlight ok, no sound or video

hi just seen this post ,i had exactly same problem some months ago
i posted it on here .
i tried to find data on those two ics (dc to dc converters ) impossible!
i had no shorts on any of the supplies on the boards ,its still waiting until i can do a comparison with another .so good luck .
remove the plastic bezel to expose the foils ,use a magnifying glass and look for any evidence of spillage ,its common for screen cleaning with spray ,allowing it to run down between bezel and panel .sometimes you can be lucky and clean the area
but more often it results in panel damage.

Hi Jimbofz,

thanks for your reply, I did read your post once I found it by searching for them ic's, yeah its a dead end for datasheets for those.

I will remove bezel and check....


here's what I've done so far, I've tried the replacement panel board by plugging in the cable from the main board and I get all the voltages, obviously the panels not connected, but this would indicate to me that the main board is not faulty

I reconnected the cable from the main board to the original panel board and decided to solder wires from gnd and 12vin of original to gnd and 12vin of replacement, checked voltages on replacement all present, then I connected wires from the replacement board to the same location where each voltage was missing on the original board.

the picture of the screen is like what I had displayed(not my photo, I didn't take one), but it was white, when I pressed fav button on remote I would get a grey shaded area covering approx. 1/4 of the screen on the left, if I exit that with remote and wait, I could see those lines moving (like the screen should be displaying no signal and moving around)

I checked again on other test points and SEQ_OUT was at 5v on replacement board and close to 0v on original, so I soldered a wire to those and this took it back to original fault, no voltages and dark blue screen, once I removed that wire it went back to the white screen and all voltages were up again.

after removing all the wires I soldered I decided to change rt6935 from replacement board to original board and guess what no change, then I changed the other one rt6939, still no change.

then I cut the track before the via for SEQ_OUT and still the same, I rechecked voltages, now I have voffe at -11v and the others at 0v or close to still.

that's as far as I got, not 100% sure I cut the track fully yet as it was late and not been back on it since.

I'm thinking of using my bench psu and feed 5v into SEQ_OUT and see what current its drawing, but I would like to trace where that via goes off to

I think I tested SEQ_OUT in diode mode and both read the same, but I will double check that, lol

any idea what or where SEQ_OUT is or goes?

[jimbofz]

Re: Sharp Aquos 40aj6ke backlight ok, no sound or video

wow, its good to see that ,like me you dont like giving up .
i give you full marks so far for effort. replacing those ic s is not for the faint hearted .
so this other panel ,was it from a working tv same model and screen size?
also something worth checking is that on these drive panels they not only have dual sided print but there are interconnecting links that run through the centre that you cant see ,its hard to explain but if the board was made of clear prespex you would be able to see these tracks of print .
i reached a dead end trying to trace connections from one component to another .
if you could have both panels side by side and join the earth points to each panel then do resistance comparisons on the various supplies.this may reveal a low resistance ,or an o/c on the original board