Sharp LC-60LE600U no op - waveforms

[legg]

Sharp LC-60LE600U will not turn on or give diagnostic indicator blinks. The indicator turns on, then off after ~10sec.
Reset procedures produce no change, though the same diagnostic indicator responded favorably to a firmware update procedure - blinking rapidly at the end of the write from the usb service port.
BU5V is present; PNLPWR, ACDET, PSON are all high during the 10sec indicator activity; unfortunately the ERR signal is also high - being terminated (along with PNLPWR) when a 1sec STBY signal occurs at the 10 sec time point.
A rough sketch of these signals and their amplitudes are attached.
Outputs to the lamp connector are also present during the 10 sec period, but the backlight is not illuminated - though one section does flash briefly as the period terminates. The voltages on these four magnetically coupled outputs is illustrated in a second attachment, showing that one sector is abnormally loaded, and that another spikes when the power cycle terminates. The spiking output produces the brief backplane flash.
I'll be replacing parts in the abnormally loaded section, in the hope that it's not the backlight section itself needing service. I suspect that the latter is a can of worms, physically, to complete.
Any other suggestions, or advice on reducing errors in backlight rework?

[dick_barton]

Re: Sharp LC-60LE600U no op - waveforms

Is the led driving voltage approx 100V per string because it looks like one set is peaking at 10 sec and is probably why the error is detected. Possibly a led is breaking down.


Read through this thread. which appears to indicate that 140V is the open circuit led voltage which is what's happening to the blue scope trace.

https://www.youtube.com/watch?v=DCXHNN8nrws

[legg]

Re: Sharp LC-60LE600U no op - waveforms

The open circuit voltages are pretty uniform, though the suspect 3rd output still has a characteristic peaky start.

The unit doesn't shut down when the lamp connector is open circuit, (end of traces occurred here when input power was removed) but there are still no diagnostic blink pattern from the power light to indicate a backplane problem.

In anticipation of a repair, I'm looking at the assembly drawings in the service manual for the display. There are only two LED assemblies illustrated, left and right - so why the four outputs?

If there are shorted leds in one string, shouldn't that string still light, even if it's pulling down the voltages to below-illumination levels on its neighbors?

[legg]

Re: Sharp LC-60LE600U no op - waveforms

Oh, yeah - all the scope traces are 50v/div; the output amplitudes barely change between the loaded and unloaded state, hanging around 90V.

You suggest that this is too low to operate a normal led string in this model.

Does this mean I need to look at loading/regulation internal to this power conversion stage?

[budm]

Re: Sharp LC-60LE600U no op - waveforms

The LED assembly has two LED strings, that is why there are 4 LED controller circuits.
Put the LED connector back in place, TV is OFF, Black probe on chassis GND.
1) Put Red meter probe or scope probe on DC and attach it to L1 -
2) Turn TV and see how high the Voltage goes up to, record the reading and then turn off the TV.
3) Move the meter probe to L2 - and repeat step 1 and 2, do the same on L3 - , L4 -.

BTW, the 90V is the feeding Voltage to the boost converter, it should go up high when 'OFL (PS-ON)' is present. You do have OFL signal, right? I do not see you report that reading.
I also do not see PNL_12V reading.
So if you leave the meter probe on any one of the L+ and turn the TV on, how high did it go up beyond 90V?

Is this your board?
http://www.shopjimmy.com/sharp-runtk...-led-board.htm
Sharp RUNTKB057WJQZ (DPS-168JP A) Power Supply / LED Board LC-60LE600U

[legg]

Re: Sharp LC-60LE600U no op - waveforms

Repeating previous test with lamp connector open, I could no longer get continuous operation from simple application of input power. This is strange, as the previous unloaded scope traces record the third time that this test was repeated.

Instead, the outputs remain for only the original loaded time period (~10sec), on power application. Pressing the Power button then produces a continual output on the unloaded connector. traces are attached.

The scope traces record:
1(yellow) +C7204 ~L1-13 connector pin
2(turquoise) +C7205 ~L1-9 connector pin
3(pink) +C7206 ~L1-5 connector pin
4(blue) +C7207 ~L1-1 connector pin

~85V is what the scope sees; a meter reads:
L1-13 85.3V
L1-9 85.6V
L1-5 77.8V
L1-1 85.7V

So you suggest that a dc-coupled boost circuit isn't running. I had assumed some kind of q-res half bridge, before noticing the lack of primary connections, or isolation. I have no schematic for the power supply board assembly - service manual only covers schematics of 'main' board.

Re two physical lamp strips / four power supply channel outputs. You mean each LED physical strip has two LED strings with a four-pin connector?

[legg]

Re: Sharp LC-60LE600U no op - waveforms

PSON was the fourth trace in the sketch of original post

[budm]

Re: Sharp LC-60LE600U no op - waveforms

My typo, it is OFL (BL-ON) pin.
I just trace out the circuit on the bottom side of the board, all the L - (Cathode return pins) are all tied together and return through Drain pin of MOSFET Q7202, and 6 SMD sensing resistors (connected in parallel) connected the Source pin of the MOSFET and to the negative Voltage boost converter circuit (L7201, Q7201, D7214) to GND. Transformer T7601 provide the Voltage (via rectifier) for the L+ (Anodes).
So check the DCV of the NEGATIVE Voltage boost converter C7234A/B, Notes: the positive legs of these two caps are connected to circuit GND.
IC7201 is the LED controller.
BTW, you do have about 380VDC on the two legs of the main filter caps on the primary side when TV is turned ON?
Also check R7601, C7603 capacitance.

[legg]

Re: Sharp LC-60LE600U no op - waveforms

The OFL pin doesn't break out into the harness of this unit. In a repetition of the lamp-loaded, line make and break trial of the first sketch, it remains low throughout. There is no subsequent effect from pressing the on button, while power is applied.
Unloaded, there's a lot of chatter on the ERR line before the STBY line is asserted, at shutdown, subsequent to an input line connection. The same chatter is visible when operation started from the power button is similarly terminated. It would be handy to know where ERR is generated and why. The chatter is new. Image attached. Previously (ie until a few minutes ago) ERR was cleared by STBY as the converter went into protective shutdown, without ambiguity (per original sketch).

In order to track down the voltage imbalance on the unloaded lamp+ terminals, I replaced the electrolytic C7206 (tested normal for c and esr) and swapped over the two film coupling caps C7201 and C7202 (both also testing normal for generic polyester), without visible effect.
It looks like the lamp +voltages are democratically limited through the IC7303regulator/PC7601optocoupler, though this may not be the main regulated voltage. The reduced voltage node (L1-5) is never seen, the spiking node (L1-1) not seen until after the converter is disabled.

PFC output is normal, around 400V when the converter is enabled. Nothing odd around R7601 or C7603.

I guess the next candidates for voltage imbalance are the MUR206's. Will also check the effect of a missing snubber cap on the unbalanced half of the anode supply.

The negative cathode voltage regulator IC7201 is MP24830, typical for this application, with data and app notes available. I'll study on it and scope a few waveforms, with lamp cathode terminal output. Supposedly, the ERR signal is generated before it's output is sufficient to forward bias the lamp strings, otherwise you'd see it, in the time frames involved here. Only the flash from L1-1 spike is visible, after ERR is asserted.

[legg]

Re: Sharp LC-60LE600U no op - waveforms

A complete change of MUR260s did not alter the unloaded voltage imbalance on L1-5, nor did it change the loaded flaring behavior on L1-1 during protective shutdown.

Loaded, the drain voltage on the drain pin of Q7202 rises above 10V before the STBY pulse inhibits the main converter. The negative output of the cathode regulator hits -60V before the inhibit. Unloaded, the negative regulator goes to -65V without generating an inhibit.

Jitter on the ERR line is only present in the unloaded lamp condition, and does not result in an inhibit.

An inhibit will only be reset by line input power recycling, suggesting a latching fault detection, either in BU5V-powered circuitry, or main board logic.

There are no indicator lamp blink codes - this is steadily illuminated when the power button permits it, turning off under the internally inhibited condition.

[budm]

Re: Sharp LC-60LE600U no op - waveforms

"So check the DCV of the NEGATIVE Voltage boost converter C7234A/B" so what do you have on those caps?
The -60V is what you are seeing?

[budm]

Re: Sharp LC-60LE600U no op - waveforms

I just found my notes about PD connector pinout: Correction about OFL pin, it is not BL-ON signal pin, it is brightness control signal.
STB is the backlights control pin.

[legg]

Re: Sharp LC-60LE600U no op - waveforms

Loaded the metered output went to -60V before inhibit.
Unloaded the output regulated at -65.

I see the STBY line only for short periods before inhibit and have begun to associate it with inhibit of main converter. ERR signal seems to accompany main converter operation, though flickering in unloaded lamp condition.

This AM, without any changes, the converter refused to start, loaded or unloaded, from line input or power button push. Only BU5V. All you see is a short glitch after line connect, too short to reach regulation, with no subsequent response from power button.

I find this inconsistency to be disturbing.

Will the main board need a firmware reflash to restore function?

Stalled - will check lamp strings with external source for Vf at If while mulling this over.

[legg]

Re: Sharp LC-60LE600U no op - waveforms

No-op explained by test point x-over. BU5V touching PNLPWR.


.....and now what could be interpreted as a lamp error flashing diagnostic signal after unloaded power connection.
This stops, never to return, when the power button and main converter are cycled on once, still unloaded.

Unexplained - no current drawn (<15uA) by lamp strings 100-175v.

[legg]

Re: Sharp LC-60LE600U no op - waveforms

Having trouble posting here. I log in, post a reply, then get a message

requesting log-in - relogging in dumps the post. This has happened three times.

So, re-typing from scratch.....

The lamp test revealed a misidentification of pins on connector L1 in my previous posts.

C7206 is actually associated with L1-9 (low output voltage)
C7207 is actually associated with L1-13 (flaring output after inhibit)

LED strings on L1-1, L1-5 and L1-9 all show similar c/v response. A 3mA knee occurs at roughly 87V. Response above 93V is approximately 14.7mA/V. (93V-50mA, 96.5V-100mA, 99.8V-150mA)

LED string on L1-13 is open circuit.

I'm wondering how an open circuit fault is detected - whether this might be bypassed in order to advance troubleshooting. Might the set not even run without it?

I'm also wondering if -65V is pretty high on the cathode regulator. Fully applied it could generate >900mA per string and draw more than double the TV set's rated input power. Might this be responsible for the actual failure in the L1-13 string?

This voltage doesn't trip fault detectors or produce an inhibit when the lamp connector is unloaded, however. Somehow the missing string current/illumination does trip the fault detectors when loaded, even though detection does not occur when, unloaded, no current flow or illumination is present in any string.

.... and still wondering why the output voltage imbalance is present in the unloaded condition.

[dick_barton]

Re: Sharp LC-60LE600U no op - waveforms

Open circuit is detected by the voltage feeding the string of leds going too high resulting in an over voltage condition being detected by the led driver IC.

If the leds are not connected then the open circuit voltage increases well beyond its running voltage which triggers the Over Voltage Protection (OVP).

[legg]

Re: Sharp LC-60LE600U no op - waveforms

The cathode regulator has an OVP through R7224/R7222/? that doesn't affect the main converter. I assume this is the one allowing the main converter to keep running when the lamp connector is unloaded.

What shuts down the main converter when the connector is loaded - the flare alone?

So I should be able to get the cathode regulator to run, loaded, with a dummy load on the open string.....

Will try this.

[dick_barton]

Re: Sharp LC-60LE600U no op - waveforms

If you know the operating voltage of the led string and the operating current then you may well be able to simulate a load. I've never tried.
Do you have a manual for this set since the details above don't mean anything to me without the schematic.

[legg]

Re: Sharp LC-60LE600U no op - waveforms

Well, that seems to allow continuous operation. Runs at about 250mA/string and ~110V across them.

The dead string leaves the left 1/4 of the screen with poor illumination.

Guess it's time to go looking for a bad connection, or bad string, as the only fault found.

Was not looking forward to this.

[legg]

Re: Sharp LC-60LE600U no op - waveforms

There is no power supply schematic in the manual I have. I'm picking up part numbers and function from the board art.