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Old 03-18-2021, 07:33 AM   #21
mzb
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Default Re: Need help hooking up LED back light strips.

1. The monitor was working perfectly. Then one day I had a red hue at the bottom left of the screen for few minutes it went way, after few days it became permanent. At the same time both the upper and lower half of the right side screen became dark.
After taking out LCD Bulb from the monitor I tried it outside and the upper tube was glowing half white and the bottom one was glowing half red.
There were no vertical or horizontal lines even after the above phenomena.
I tried the jumper modification after ordering another one. I was not worried about the warranty, because by then the seller has refunded the money without any hassle.
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Old 03-18-2021, 10:53 PM   #22
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Smile Re: Need help hooking up LED back light strips.

Hi mzb,

From your post #16 of the led board ca-155, the dc input required is 10~30vdc.
So i think your dc input of 18.6vdc from your post #19 should be sufficient to light up the led strips.
Have you rechecked all the vin, ena, dim, ground connector are all soldered securely to your Dell board? Vin is your 18.6vdc while ground connector to any ground screw holding point.
Btw, where do you connect the ena and dim connectors? After you connected everything in order and switched on the ac power did you noticed any blue light from your led power on switch? Or any sign of light from the led strip? Maybe you can try unsolder the shorted regulator on the led board and try switch it on.

Last edited by mikey5791; 03-18-2021 at 10:56 PM.. Reason: Add comment on ena connector
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Old 03-19-2021, 12:15 PM   #23
mzb
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Default Re: Need help hooking up LED back light strips.

Hi mikey,
Yes I have reckecked all the vin, but I will resolder them again, just to satisfy myself.
The Dim and Start wires are soldered to the heads on Power board from where they go to the Logic Board. Have a look at the photo attached.
File Type: jpg 20210317_151311.jpg (64.5 KB, 4 views) which is attached to my previous letter.
When you press the Power On switch, there is a LED which glows properly as it has always done when the monitor was working. There is no sign of light at the led strip when it is switched off. Anyway I will resolder VIN wire again. Because these two boards from different supplier should not behalf the same. Or there is a problem with the LED strip. I have tried one strip at a time with same result.
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Old 03-19-2021, 06:46 PM   #24
mikey5791
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Default Re: Need help hooking up LED back light strips.

Hi mzb,

Haha my overlook at this File Type: jpg 20210317_151311.jpg (64.5 KB, 4 views). Saw it at your post #19 but the picture was a bit blurry. I trust that all your Vin,ena,dim connections are in order.

You mentioned "When you press the Power On switch, there is a LED which glows properly as it has always done when the monitor was working. " I guessed the LED which glows is the normal blue color led indicating power is on. Was there any light emitted from your led strip or more accurately from your monitor screen at the same time you noticed the LED glow.

Later you mentioned "There is no sign of light at the led strip when it is switched off. " Sorry i do not quite understand this comment. Are you saying that when you switched off ac power, there is no light at the led strip. But is there light at the led strip when the ac power is switched on? Maybe i got confused with your LED(already built in your monitor switch panel) and your led strip(those two strips you bought).

Btw, is it the same type of led board with the new led strips that you bought previously? I meant with the same placement of red vin, yellow ena, yellow dim, black ground on the led board., and dc input of 10~30vdc? You can test if the led strip is good or bad by placing your dc supply of 4.5~6v(preferably from a battery pack) on every 3 led connections on the side. Probe your dc supply red positive to your led positive side and black negative to your led negative. If the 3 leds glows, then you can proceed to check the next 3 leds until you tested the whole strip to make sure there is no dead or bad led in between.
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Old 03-19-2021, 06:56 PM   #25
mikey5791
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Default Re: Need help hooking up LED back light strips.

Hi mzb,

Another suggestion for you before you resolder those vin, ena, dim connections is placing shrink wrap tubing or electrical tape to prevent exposed wire accidentally touching other parts of the power supply board which may cause short circuit. I noticed your two yellow wire, the ena dan dim are very close to each other and do hope they are not in contact to each other.
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Old 03-22-2021, 08:53 AM   #26
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Default Re: Need help hooking up LED back light strips.

Regarding your letter No.24, I am attaching photos of both the new and old boards. They are exactly the same, axept new one has a Cap. before the headers. As far as your suggestion of insolating the connection, I would do it when the whole setup start working. If you refer to my letter No.17, these strips start glowing at 7volts and fully at 9 volts. What I am getting is only 6.5 volts at the header when only one strip is attached and it drops to 6.3V when both the strips are attached. I did change the Vin at another place but the results are the same. Very frustrating and disappointing.
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Old 03-22-2021, 11:08 AM   #27
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Default Re: Need help hooking up LED back light strips.

You can NOT short that transistor! This is NOT a REGULTOR IC. That is the boost output that BOOSTS the voltage to the led string. When you shorted that transistor the way you did D~S you likely damaged the board.
J1 is a jumper to ground, R7 & R4 are source resistors, R6 is in the current sense line back to the ic. If you shorted the mosfet, you likely opened R4&7 which then damaged the ic.
What you are doing creating a short across Vin from one end of the coil through the shorted mosfet, through R4/R7/j1 to ground.
Attached Images
File Type: jpg 20210317_144134.jpg (16.3 KB, 2 views)

Last edited by R_J; 03-22-2021 at 11:21 AM..
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Old 03-22-2021, 03:03 PM   #28
mzb
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Default Re: Need help hooking up LED back light strips.

Hello R_J, thanks for your comments. I am not at all very well versed in electronic, and you have seen the example of me shortening the IC. I would appreciate it very much if you could shed some light on why these boards are not delivering the required voltage to the strips to light them up. As I have mentioned in my previous letters that I am injecting about 20V but I am only getting 6.5 volts at the strips headers. I have tried both the boards from different suppliers, the result is the same. Have a look at the pics. I am attaching.
Attached Images
File Type: jpg 20210321_155501.jpg (48.6 KB, 3 views)
File Type: jpg 20210321_155545.jpg (36.8 KB, 3 views)
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Old 03-22-2021, 05:35 PM   #29
R_J
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Default Re: Need help hooking up LED back light strips.

Can you provide the ic number, is it DF6113. The board that has the mosfet shorted out seems to be missing the output capacitor.
This is where it gets confusing, The ENA line needs to be around 3 volts to turn on the ic but has a maximum input voltage of 5 volts. I would leave the dim line alone and see if you get any leds lit up, then short the dim line to ground and see if they get brighter.

The ic on these boards has a Minimum of 5v and a maximum vcc of 24volts, not the 30v marked on them.
Try running it off the +5v from the board and not the +19v Or try using a 9v battery for testing

Last edited by R_J; 03-22-2021 at 06:22 PM..
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Old 03-23-2021, 10:19 AM   #30
mzb
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Default Re: Need help hooking up LED back light strips.

Hi R_J thanks for your letter, yes it is indeed DF6113. I just found out that one of the strip has short circuit, if I detach it the other one lights up more. Let me sort out the strips first then I will do what you wrote in your letter. I will come back to you.
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Old 03-26-2021, 02:56 AM   #31
mikey5791
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Smile Re: Need help hooking up LED back light strips.

Hi R_J,

You mentioned that "Try running it off the +5v from the board and not the +19v Or try using a 9v battery for testing". May i know how to use a 9v battery for testing the led back light strips? Is the red vin and yellow ena wire both connected to the positive side of 9v battery and black ground to the negative side? If you don't mind, can you explain in detail.
I am curious to learn so that next time i can use this method for testing.
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Old 03-26-2021, 08:37 AM   #32
mzb
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Default Re: Need help hooking up LED back light strips.

I found out the problem I am having. As suggested by mikey5791 in his letter No.24, I tested the LED Strips with a 4.5v pack of batteries, and I got strange and wired results. in one strip if the first 3 LEDs tested no glow but the last LED on the strip would glow. If the first 2 LEDs tested, they wont light up, but the 3rd would. and so one, but you can not predict which one would glow.
Anyway I have ordered another set of strips, which I would receive some time in April.
I am also having problem with the display. I am getting vertical and horizontal lines when using shorted board, and I found that LQFP Chip MAX8795A on T Con board is getting hot. I do not know if the lines are due to this chip or what. I can not find this chip in LQFP format but they are available in QFN format.
Is there any alternative to this chip ? Thanks for your help.
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