I have TCL 55s405, originally diagnosed it with no power. The fuse and caps were fine. Measured the voltage from the powerboard and the output pins were 0volts. There are pictures of the boards in this post [url]https://www.badcaps.net/forum/showpost.php?p=971997&postcount=20[/url] Nothing obvious on the powerboard is the issue, but that's on hold until I can verify the rest of the unit works.
Decided to bypass the powerboard and I put 12volts directly to the mainboard and applied 216 volts to the backlight. The backlight seems to be fine and turns on as expected. The mainboard...
leggot
Senior Member
Last Activity: 03-04-2023, 06:23 PM
Joined: 10-13-2014
Location: San Jose, CA
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TCL 55s405 No Power, No Display
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Re: Dell S2715Ht LED backlight
Also, I seem to have mixed up the films that go between the backlight and the panel. There are two semi transparent films and one that is somewhat reflective (like a mirror).
Currently the two transparent ones are closer to the LEDS and the reflective one is near the panel. The light looks distributed from only one angle. Does anyone know what order these films should be in?
Thanks -
Re: Dell S2715Ht LED backlight
Hi all,
I figured out how to solve the problem - I found a comparable LED (3V and 0.5W) and soldered it into the green wire circuit - to provide the voltage drop necessary. I removed the broken LED from the strip and jumped the two positions. The monitor works - despite missing one LED at the end of the strip.
Thanks againLeave a comment:
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Re: Dell S2715Ht LED backlight
Thanks for the help. I think some of the previous calculations may be off by a bit, the high is 60volts and low is 20volts, thus the difference is 40 volts.
40/15 = 2.67 volts per led, removing one led from the circuit would yield 40/14 = 2.86 volts per led.
This site seems to reference the lamp voltage as 46.5, thus 46.5/15 = 3 volts. [url]http://www.panelook.com/LM270WF7-SSA1_LG%20Display_27.0_LCM_parameter_23622.html[/url]
Since the voltage per each in a string of 14 leds is less than the datasheet's expected...Leave a comment:
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Re: Dell S2715Ht LED backlight
Hi,
I am sorry, but I am still rather confused. I think I understand how the circuit works and thanks for finding all the documentation and being patient with me.
What I don't know is what to try next. I have already identified the specific LED that is broken, it doesn't light up when a small voltage is applied to it. Should I attempt to find a replacement LED or try something else?
ThanksLeave a comment:
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Re: Dell S2715Ht LED backlight
Sorry, are the LEDs are in series or parallel? From your previous statement, I would assume parallel, thus not requiring a jumper; simply remove the broken LED from the circuit.Leave a comment:
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Re: Dell S2715Ht LED backlight
It appears as if all the LEDs turn on except for the one at the end of the strip. Will attaching a jumper wire around this LED allow the circuit still function as normal?
It is odd that it is the LED at the end, is this an indication that it burned out from over voltage or failure in another part of the circuit?Leave a comment:
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Re: Dell S2715Ht LED backlight
First I disconnected the green wire - this led to 3/4 of the led string to function as intended.
Upon swapping the green wire with the black wire, the same 3/4 of the string functioned; however now the string tied to the green wire doesn't turn on when it was reattached. Possibly the green wire string broken when it was attached to the black wire.
Is there a way to test each LED individually? It would be acceptable to swap that one with an LED that is removed from the end of the string - that position would just have a jumper...Leave a comment:
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Re: Dell S2715Ht LED backlight
Ok, comparing the voltages to the chassis ground:
All the voltages decline after spiking at the voltages listed below.
Green - 12v (this is what the multimeter says, I think it spikes higher, but it is difficult to tell as the multimeter 'thinks' for a second then displays the voltage)
Yellow - 20v
Orange - 60v
Red - 60v
Brown - 20v
Black - 20v
Also, one string of leds stays on for about a second longer than the rest - possibly corresponding to the green wire?Leave a comment:
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Re: Dell S2715Ht LED backlight
L702 jumps to about 60v and returns back down to 19-20vLeave a comment:
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Re: Dell S2715Ht LED backlight
From what I can tell, all the LEDs do work, the entire strip flashes momentarily when the unit is first turned on. This leads me to believe this is an issue with the circuitry that controls the power going to the LEDs.
I am not opposed to by passing this circuit and simply applying voltage to the LEDs independent of the circuitry; however it would be nice to be able to dim the monitor.
I am not sure if this answers your answer, I'm not sure if this proves that all the LED strips are functioning correc...Leave a comment:
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Re: Dell S2715Ht LED backlight
Actually, there are 60 leds, it is rather difficult to take a picture of the entire panel. In the momentary flash, it appears as if all the leds light up, however it is difficult to verify all 60 leds do flash.Leave a comment:
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Re: Dell S2715Ht LED backlight
I apologize, here are the corrections
R732 - Green to pin 1
R733 - [B]Yellow [/B]to pin 9
R734 - Brown to pin 11
R735 - [B]Black [/B]to pin 12
L702 - Red and Orange (tied)Re: Dell S2715Ht LED backlight
I apologize, here are the corrections
R732 - Green to pin 1
R733 - [B]Yellow [/B]to pin 9
R734 - Brown to pin 11
R735 - [B]Black [/B]to pin 12
L702 - Red and Orange (tied)Re: Dell S2715Ht LED backlight
I apologize, here are the correctionsLeave a comment:
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Re: Dell S2715Ht LED backlight
Hi,
Thanks for the quick reply.
I noted the following were connected:
R732 - Green to pin 1
R733 - Black to pin 9
R734 - Brown to pin 11
R735 - Black to pin 12
L702 - Red and Orange (tied)
The IC says GB98AGN CF7NIN 1448A2 at I701. I couldn't find an easily accessible datasheet, I emailed a place; we will see if they respond.
According to this russian forum, the hp elite display e221c has the same chip. This might give us some insight to the led driver of the dell,...Leave a comment:
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Re: Dell S2715Ht LED backlight
[URL=http://s876.photobucket.com/user/gotlego/media/f81fe7b3-7f2d-4ddc-b90f-7b4a5a1429d6.jpg.html][/URL]
[URL=http://s876.photobucket.com/user/gotlego/media/IMG_18911.jpg.html][/URL]
[URL=http://s876.photobucket.com/user/gotlego/media/IMG_18921.jpg.html][/URL]Re: Dell S2715Ht LED backlight
[URL=http://s876.photobucket.com/user/gotlego/media/f81fe7b3-7f2d-4ddc-b90f-7b4a5a1429d6.jpg.html][/URL]
[URL=http://s876.photobucket.com/user/gotlego/media/IMG_18911.jpg.html][/URL]
[URL=http://s876.photobucket.com/user/go...Leave a comment:
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Dell S2715Ht LED backlight
Hi all,
I have a dell S2715ht, it has an led strip backlight and has an odd problem, the led strip turns on for about a second before turning off. The monitor power led stays on and shining a flashlight into the screen reveals a good picture.
I was able to crack the monitor open and test the voltages going to the led strip, the led strip lighted momentary so I only got readings at that one given instant.
The led/lcd panel is an LG LM270WF7. I would be satisfied using an external power source to power the LED backlight, independent of the monitor; however... -
Re: Viewsonic VA2323wm - No Backlight/Intermittent Power/buzzing transformer
I swapped the transformer, a good powerboard with the bad transformer and the unit fails to turn on, a swap the opposite way seems to have blown a resistor on the t-con board. This is just seems really sketchy and the transformers are a pain to unsolder. Perhaps Ill mess with these guys another time, but if you can figure it out, that would be great!Leave a comment:
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Re: Viewsonic VA2323wm - No Backlight/Intermittent Power/buzzing transformer
Ok, its odd that you mention the mosfet near the transformer. I tested the resistance between the pins, but they seem to behave similarly. There is some heat damage near it, indicating that it possibly may be malfunctioning.
I suppose the only way to know for sure, is to swap the transformer and the mosfet to see which one solves the problem. In the event that the transformer seems to be the issue, what would be my best course of action? Transformers seem to be non standard - unlike capacitors....Leave a comment:
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Re: Viewsonic VA2323wm - No Backlight/Intermittent Power/buzzing transformer
Hi,
I'm not quite sure what you are saying, but I did try the good powerboard with the bad monitor and everything functioned correctly. The bad powerboard also failed when tried with the good monitor, thus I have tested the CCFLs....Leave a comment:
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Re: Viewsonic VA2323wm - No Backlight/Intermittent Power/buzzing transformer
Hi,
Thanks for replying. I am planning to replace the bulging cap when I put all the monitors back together.
I am not particularly familiar with the internals of transformers, but there are 8 pins, two large ones with 510 ohms between them. There there are six pins that all seem to have very low resistance between them (about 1 ohm). Now the difference between any of the small pins and a larger one is 10M ohms for the good board and 6M ohms for the bad board. The picture is reposted...Last edited by leggot; 10-02-2016, 01:17 AM.Leave a comment:
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