Sharp Aquos LC-46XD1E no power-up

[Khron]

Greetings,

Where to start... A few weeks ago i landed a gorgeous-looking Sharp LC-46XD1E, with video that supposedly would cut out soon after power-up, for a mere 20euros. Cosmetically impeccable, i just got the remote for it in the mail today (previous owner forgot to bring it along).

Now... Upon plug-in (power led lights up red) and power-up (green), the relay in the PSU clicks, and after about one second it clicks back, and the power led gives a pair of red flashes every second. According to THIS, it's either the inverter unit or the LCD panel.

With the help of advice from dad and a couple other friends, i've pretty much ruled out the power supply (including disabling some parts of it that might have caused it to turn back off. The relay that clicks only bypasses the thermistor on the AC input.

Dad got a pdf with the service manual for 5$ (192 pages, 66MB), and that helped somewhat with the PSU troubleshooting, but the schematic of the inverter is only at a simplified level. The inverter controller is BD9886FV, with one of the "thinnest" datasheets i've seen yet. The block diagram of the chip is slightly more revealing (a couple external components drawn), but not by much.

I've tried starting the tv in "service mode" as per the service manual, but all i get is the behaviour outlined above.

I've also made some voltage measurements in stand-by and in that one-second "on" state, so feel free to ask for "probings".

It'd be just soooooo great to be able to revive this baby... I'm looking forward to any tips / ideas you guys (and gals?) might have...

[PlainBill]

Re: Sharp Aquos LC-46XD1E no power-up

"A picture is worth a thousand words". While I appreciate the link to the datasheet, the service manual would be more help.

The key to solving this is determining IF there is a status line returning from the inverter to the main board, and IF that status line signals a problem. A picture of the inverter may go a long way toward answering those questions.

PlainBill

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

I've already checked elektrotanya, and that 6MB file is strictly the few pages of schematics from the service manual, all with the exception of the (cursed) inverter boards.

There *IS* a return line from the inverter to the main board. It's on pin 5 of the 9-pin "LB" connector. In the block-diagram for the inverter controller, you can see that it has a "FAIL" pin, that's pulled up through a resistor. I measured that LB pin 5 today, and it sits around 1.35v at stand-by, and my multimeter caught a maximum of 2.8v before the relay clicked off and it entered that two-red-flash protection mode.

The inverter is made up of four boards. Board 1 (top left, seen from the back of the tv) has two transformers and six lamp connectors, board 2 (lower left) has three trafos and six lamp connectors, and also contains the inverter controller. Board 3 (top right)similar to board 1, but with three trafos and six lamp connectors, and board 4 (lower right) is nearly identical to board 2 (as in, it has two pairs of switching FETs, but it gets the signals from board 2).

I'm attaching a "stitched-together" simplified schematic of the inverter boards 1-2, as well as a couple of shots of the actual thing, including two shots of the solder side of board 2 (with the controller).

[PlainBill]

Re: Sharp Aquos LC-46XD1E no power-up

The schematic didn't come through. I did look through the partial schematic and noted a 'BL_FAIL' signal line. I also noted a 'backlight on' control line

Are there any signs of the backlights coming on, even for a fraction of a second?

Have you checked the resistances of the secondaries on the inverter transformers? Depending on the design, some inverter controllers react to a fault condition by shutting down within a fraction of a second.

PlainBill

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

The schematic should be in the .zip file (since the .gif wouldn't get attached full-size).

No sign of backlight attempt of coming on.

All the secondaries measure between 2,09-2,11kohm, so at least that part seems ok...

[PlainBill]

Re: Sharp Aquos LC-46XD1E no power-up

The schematic should be in the .zip file (since the .gif wouldn't get attached full-size).

No sign of backlight attempt of coming on.

All the secondaries measure between 2,09-2,11kohm, so at least that part seems ok...

The .gif file gave me nothing but a blue column. Suggestion - save and attach it as a .jpg file.

With no backlights the logical step is to check all the fuses on both inverters, and (of course, the 'On' signal).

PlainBill

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

The two fuses on boards 2 and 4 respectively, are good. Just today i was thinking of perhaps pulling and testing the four sets of switching FET's, "just in case"...

Fingers crossed for the schematic this time

EDIT: One more thing: which connector (and pin) is that "On" signal supposed to be on?

EDIT 2: Ah, nevermind, found it, pin 4 on connector PB. I blame the early and horrible wake-up my next-door neighbour "arranged", with drilling walls and sawing and whatnot...

EDIT 3: Just measured, pin 4 (INV_ON) doesn't budge, stays at zero volts.

[PlainBill]

Re: Sharp Aquos LC-46XD1E no power-up

The two fuses on boards 2 and 4 respectively, are good. Just today i was thinking of perhaps pulling and testing the four sets of switching FET's, "just in case"...

Fingers crossed for the schematic this time

EDIT: One more thing: which connector (and pin) is that "On" signal supposed to be on?

EDIT 2: Ah, nevermind, found it, pin 4 on connector PB. I blame the early and horrible wake-up my next-door neighbour "arranged", with drilling walls and sawing and whatnot...

EDIT 3: Just measured, pin 4 (INV_ON) doesn't budge, stays at zero volts.

Well, that is a clue.

PlainBill

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

Is that (connector LB, pin 4) the pin / signal you meant?

[PlainBill]

Re: Sharp Aquos LC-46XD1E no power-up

Is that (connector LB, pin 4) the pin / signal you meant?

I didn't trace the signal that far; all I wanted to do is confirm that the inverter COULD put out a 'failed' signal - many do not. The fact that the INV_ON signal never goes high is a problem, and may be the source of the failure. What I do in cases like that is see if I can isolate the input of the inverter from the control source and force the input high to see if the inverter does work. (As a rule, I NEVER force a signal line high or low unless I know the driving circuit will tolerate it.)

PlainBill

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

I'm gonna pull the FET's out today and test them, and if they're all ok, i'll see how i can (safely and non-destructively) pull the INV_ON pin out of the connector so i can pull the signal low or high and see what happens.

Could you perhaps indicate where on the schematic you found the "BL_FAIL" and "backlight on" signals?

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

Well, from what i can tell, the switching FET's are all ok. There are four pairs of P/N FET's (2SK3706/2SJ655). My multimeter puts out about 2V for diode test. After charging the gate, the D-S voltage drop starts around 2mV for the P's, and within 2 seconds rises to above 2V, showing "OL" on the meter, and at 1,7V for the N's, going OL at the next measurement (within half a second).

Guess it's time for the PSU to come off and see what the "INV_ON" pin connects to (although on the detailed schematic of the PSU, it's apparently connected to nothing, but i'll check the board).

I'm open to any other ideas / tips you might have...

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

Indeed, pin 4 of the connector LB is a "dead end" on the pwer supply board (not going anywhere, not connected to anything).

I'm lost here...

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

Ok, SOME progress: measuring pin 2 of connector LB (signal STB as in "stand-by"; high = inverter on, low = inverter off). It doesn't budge from 0v, so the main board doesn't even try to turn on the inverter. Since it's off, that qualifies as an inverter malfunction, hence the quick shut (back) down.

Should i be preparing to order a spare main board from fleaBay?

UPDATE: I removed the wire strap leading from LB pin 2 to the STB pin of the inverter controller, and pulled STB to Vcc through a 1k resistor. Result: it still shuts back down after that one second, BUT the backlights lit up!!!

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

In case it might help, i've shoved the service manual up on my Dropbox page, so for those interested, the link is HERE.

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

Hmmm... A(nother) friend threw in the idea that the LVDS (aka Tcon) board might be faulty (which would be consistent with the blink code list in the first link in the initial post).

[rmoody]

Re: Sharp Aquos LC-46XD1E no power-up

Hmmm... A(nother) friend threw in the idea that the LVDS (aka Tcon) board might be faulty (which would be consistent with the blink code list in the first link in the initial post).

unplug the Tcon cables and power on and see if you still have the same problem. From my limited experience, when a tcon is bad the inverters will power the backlights but won't display a picture.

[rayrod81]

Re: Sharp Aquos LC-46XD1E no power-up

On most Sharp TVs if the T-Con is not working then the TV will go into protect and not turn. If you unplug the T-Con from the main board then the TV should turn on and show backlights. If this happens then you have a faulty T-Con or possibly a bad panel.

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

No go... Behaves the same way.

One at a time, I've unplugged:
1) the two ribbons from the Tcon to the LCD panel,
2) the LVDS cable from the mobo to the Tcon board,
3) the 4-pin data (?) cable from the mobo to the Tcon board (into which the 12v from the PSU also get)

I did some more investigating today. Upon power-up, the 12v for the Tcon board never goes on. According to the PSU schematic, that's activated by a signal coming from the mobo (straight from a pin of the main CPU / FPGA), which never goes high. To me, that would point "back" to the mobo being the main suspect.

If the Tcon board never gets powered on, "of course" that whatever's still working on the mobo will sense the error and shut the PSU down.

--- Later update ---

1) I took off the "digital board" (card reader) from on top of the mobo, and started poking around, measuring the outputs of the various voltage regs. Following the schematics, I noticed that the "POW_LCD" signal (to enable the 12v for the Tcon board) was supposed to be pulled-up to 3.3v, but it measured as zero, both in stand-by, and during the 1s on-time. All the regs i checked had the correct outputs, until i got to IC1707, a Sharp 20WZ11 which was supposed to provide a 3.3v bus upon power-up; instead, the output was around 70mv during power-up. Took the mobo out, measured the passives around it, got some odd resistor values, then i measured the resistance between all its five pins, and lo and behold, between Vout and Gnd i got 0.3ohm or so.

2) I carefully unsoldered that reg, and no more short between its Vout and Gnd; just to double-check, i measured the pads, and sure enough, (pretty much) dead short.

3) Following the schematic, i traced that specific 3.3v line to all the ferrite beads it went through. At long last, upon removing FB1903 and measuring between the non-grounded end of the capacitor after it, *beeeeep* ie. short to ground. Looks like the HDMI receiver chip is shot...

[Khron]

Re: Sharp Aquos LC-46XD1E no power-up

Spare mobo arrived yesterday (ebay.co.uk ), popped it in, and it took right off

Last night, with the help of a neighbour, i propped it up on its "pedestal"