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Old 04-25-2019, 12:24 PM   #1
imaddicted2u
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Default RCA RDLDED3258A-C No back light

32" LED. Single board, integrated T-con.
Has sound back light never comes on. Can see menu using flashlight.
Connector to LEDs measures:
Standby 37.7v
On 40.9v for 5 seconds, jumps to ~106v drops to 43.2v over ~10 seconds.
Same with LEDs disconnected.
My first time inside a LED TV, I'm guessing open LED or LEDs in the strip...
The connector feeding the LEDs measures open too.
Anyone have thoughts or tips?
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File Type: jpg 20190425_145102.jpg (717.0 KB, 3 views)
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Old 04-25-2019, 01:35 PM   #2
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Default Re: RCA RDLDED3258A-C No back light

Sounds like you have open circuit in the Load (LED's string circuit).
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Old 04-25-2019, 01:46 PM   #3
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Default Re: RCA RDLDED3258A-C No back light

Thanks budm, for being ever helpful, much appreciated.
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Old 04-25-2019, 01:52 PM   #4
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Default Re: RCA RDLDED3258A-C No back light

There are two wires on that LED connector, keep black probe on the chassis, red probe on one of the two wires hen turn on the TV and see how high the Voltage jumsp up to and settle down to, the more the red probe to the second wire and repeat the test.
You may have to use skinny probe tip to get to the connector pin at the wire entrance to the connector.
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Old 04-25-2019, 03:06 PM   #5
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Default Re: RCA RDLDED3258A-C No back light

Chassis to:
Off On
Black 0v 0v
Red 37.7v 43.0v for 5 seconds, jump to ~105v drop to 43.1v over ~10 seconds
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Old 04-25-2019, 06:51 PM   #6
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Default Re: RCA RDLDED3258A-C No back light

Quote:
Originally Posted by imaddicted2u View Post
Chassis to:
Off On
Black 0v 0v
Red 37.7v 43.0v for 5 seconds, jump to ~105v drop to 43.1v over ~10 seconds
OK, since you do not get any Voltage readings on the LED string return line Black wire, that means you have open circuit in the LED string some where, it can be open LED, open connections between LED strips, etc.
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Old 04-25-2019, 07:04 PM   #7
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Default Re: RCA RDLDED3258A-C No back light

Poor mans LED tester...CR1620 button battery, some wire and a plastic clothes pin...lol
2nd LED from left in the top strip did not light up.
I wonder if I could replace the single LED with one like this?
https://www.ebay.ca/itm/100pcs-lot-l...IAAOSwk2tcvuD9
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Old 04-25-2019, 08:03 PM   #8
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Default Re: RCA RDLDED3258A-C No back light

Quote:
Originally Posted by imaddicted2u View Post
Poor mans LED tester...CR1620 button battery, some wire and a plastic clothes pin...lol
If you put your meter in diode/continuity mode and touch the leads to the proper sides of the LED, they will glow faintly too.

I replaced an individual LED on a strip using a standard heat gun. Not the best way to do it, but it got the job done. See the video here. https://youtu.be/7bOx-CVTG1g

Iíve since purchased a dedicated hot air rework station.
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Old 04-25-2019, 08:48 PM   #9
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Default Re: RCA RDLDED3258A-C No back light

Thanks earz. Good video. I thought I tried checking the LEDs on diode test but maybe the room was too bright.
I just stumbled upon a video for this model set. After repair he lowered the LED current by changing some resistors.
https://www.youtube.com/watch?v=S2_WtM5DMx0
Apparently this TV doesn't have a back light adjustment on the menus so the LEDs run at full brightness.
I read in a thread here:
https://www.badcaps.net/forum/showpo...5&postcount=12
that there is a service menu accessible by MENU-1-1-4-7 where the back light can be turned down. I'll check it when I can see the menus but I wonder, wouldn't that reduce the LED current to prolong the LED life, instead of changing resistors?
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Old 04-25-2019, 09:05 PM   #10
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Default Re: RCA RDLDED3258A-C No back light

You need to verify the foot print to see if the big pad is Anode or Cathode, that is one of the important spec. You also need to check the dimension of the LED. 350mA is alittle bit on the low side, I expect it to be around 400mA rating or more, but if you lower the backlights level it may be OK.
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Old 04-25-2019, 09:22 PM   #11
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Default Re: RCA RDLDED3258A-C No back light

budm, I'll take a closer look at the LEDs. I picked that one from ebay because it's mentioned as replacement used in this video, for this model set.
https://www.youtube.com/watch?v=S2_WtM5DMx0
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Old 04-25-2019, 09:26 PM   #12
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Default Re: RCA RDLDED3258A-C No back light

Quote:
Originally Posted by imaddicted2u View Post
budm, I'll take a closer look at the LEDs. I picked that one from ebay because it's mentioned as replacement used in this video, for this model set.
https://www.youtube.com/watch?v=S2_WtM5DMx0
If that is the correct information then it should be fine, it is always good to verify since you do not want to take the panel apart again in the future. Same model of TV may use different version of the board or different LCD panel manufacturers.

Last edited by budm; 04-25-2019 at 09:34 PM..
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Old 04-25-2019, 09:27 PM   #13
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Default Re: RCA RDLDED3258A-C No back light

Right on, thanks for your good advice...again.
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Old 04-26-2019, 05:23 PM   #14
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Default Re: RCA RDLDED3258A-C No back light

budm
I measured the LED, does 2835 sound right? I had a LED strip with the same size LEDs, installed one but the back lights only blinked for a second then the replacement went open. Too low a current rating I assume.
Would this be a good choice or would you suggest something else?
https://www.ebay.ca/itm/3528-2835-3V..._MLXCip2CGw91w
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Old 04-27-2019, 01:03 AM   #15
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Default Re: RCA RDLDED3258A-C No back light

3528, 3535, 3030 are the typical size but did you actually measure the ones being used in your strips?
The one in you link has big solder pad as Cathode.
What kind of footprint does your LED have?

Last edited by budm; 04-27-2019 at 01:04 AM..
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Old 04-27-2019, 04:03 AM   #16
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Default Re: RCA RDLDED3258A-C No back light

Measured the one I took out with a caliper. Oops, the pics I attached yesterday didn't go.
Attached Images
File Type: jpg led strip numbers 1.jpg (724.5 KB, 5 views)
File Type: jpg led strip numbers 2.jpg (625.5 KB, 5 views)
File Type: jpg led strip numbers 3.jpg (575.1 KB, 5 views)
File Type: jpg led strip numbers 4.jpg (945.2 KB, 11 views)
File Type: jpg 20190426_071611.jpg (396.9 KB, 7 views)
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Old 04-29-2019, 03:21 PM   #17
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Default Re: RCA RDLDED3258A-C No back light

Is there a way to identify the SMD LEDs on the back light strip? I've seen 3528's at 3 volt, 6 volt and 1 watt and 1.5 watt. Although 3 volt at 1 watt seems most popular.
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Old 04-29-2019, 03:40 PM   #18
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Default Re: RCA RDLDED3258A-C No back light

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Last edited by neilc6; 04-29-2019 at 03:45 PM..
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Old 04-29-2019, 09:13 PM   #19
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Default Re: RCA RDLDED3258A-C No back light

It will be 3V 1W LED due to the fact that you can light it up with 3V, the 6-V on will not light up with 3V. The large pad is Cathode (-) for your LED (https://www.badcaps.net/forum/attach...5&d=1556359360).
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Old 04-30-2019, 10:19 PM   #20
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Default Re: RCA RDLDED3258A-C No back light

I found these 2 LEDs, both say 1 Watt rating but one is rated at 350ma, the other at 280ma. Do you think it would be best to go with the higher rating?

https://www.ebay.ca/itm/100pcs-lot-n...EAAOSwJbFckv~t

https://www.ebay.ca/itm/3528-2835-3V..._MLXCip2CGw91w
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