LG42PC3D -UD originally with green lamp but no display or audio.
Owner says was working, then went 'pop'.
All 5V caps bulging. replaced.
All PSU output voltages within spec but -Vy is low on YSUS.
One of three parallel fets between SUS_OUT and SUS_DN is zenering,
eventually shorts DG. Replaced all 3 - -Vy now OK.
Y scan buffer test point does not follow YSUS output below -50V
Note: This unit seems to expect YSUS output to park at -Vy in between
drive signal pattern periods. A replacement drive signal board confirms this....
legg
Member
Last Activity: 11-17-2022, 11:18 AM
Joined: 04-26-2018
Location: ontario
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LG 42PC3 buffer output doesn't follow YSUS
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Re: Sharp LC-60LE600U no op - waveforms
A firm 'itive'.
Considering the flammability of the materials in one of these displays, I might sympathize with the protective function used in the thing, however I'm guessing it was just easier/cheaper to do. Given the reluctance of the bad string to arc on a flare, or draw anything when probed to double normal voltages in testing, there seems little likelihood of it doing so in the future, unstressed and cold.
I've attached a schematic of the final plate assembly used. Drawing from the junk pile, it used metal... -
Re: Sharp LC-60LE600U no op - waveforms
I rigged up a more rugged substitute with the right profile, then showed the result to my neighbor, for whom I'm doing the work as a favor. He didn't seem distressed by the darkish corner of the resulting display. He knows how much the replacement lamp will be and knows the amount of work involved.
Wrap it up, he says. He'll live with it.
I suspect a lot of owners would have said the same, if, in the original design, one lamp section failure didn't cause the whole unit to die.
Imagine other equipment...Leave a comment:
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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.Leave a comment:
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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.Leave a comment:
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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.Leave a comment:
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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...Leave a comment:
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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.Last edited by legg; 04-29-2018, 08:44 AM. Reason: missing copied line from previous posting attemptLeave a comment:
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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...Leave a comment:
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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...Leave a comment:
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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...Leave a comment:
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Re: Sharp LC-60LE600U no op - waveforms
PSON was the fourth trace in the sketch of original postLeave a comment:
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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...Leave a comment:
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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?Leave a comment:
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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...Leave a comment:
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Sharp LC-60LE600U no op - waveforms
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... -
Re: New Members - please post your introductions here
Rob Legg in TO. Just trying to follow the guidelines for posting. Have a Sharp LC-60LE600U with no screen display or blink codes, that has accepted a firmware update. Have scoped signals and voltages that I'd like advice on.Leave a comment:
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