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Old 02-20-2021, 03:58 PM   #1
anupkg1985
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Exclamation Samsung UN55JU7500F

Hi,
I have got a 55 inch Samsung curved tv, it doesn't power on. There is no backlight, audio or video. I could see backlight on if mainboard is disconnected from smps board. I suspect the main board is culprit. Below are the readings I get on board -

Stand by voltage 13V
PS ON 4.5V
BLU ON 3V
OD ON/OFF 3.6V
ANA DIM 3.3V
OD Level 3.6V

Also the voltage on main caps is jumping from 391V to 168V continuously.
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File Type: jpg 20210220_134320.jpg (1.11 MB, 17 views)
File Type: jpg 20210220_134359.jpg (652.1 KB, 10 views)
File Type: jpg 20210220_134339.jpg (1.46 MB, 18 views)
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Old 02-20-2021, 09:43 PM   #2
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Default Re: Samsung UN55JU7500F

1) So if you run the power supply board by itself, does the PFC Boosted Voltage stay at 390VDC?

2) If all boards are connected. When TV is turned on, does the PSON stay at 4.5V or it jumps up and down?

3) Can we see the pictures of the whole backside of the TV showing all boards?
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

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TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809

Last edited by budm; 02-20-2021 at 09:44 PM..
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Old 02-20-2021, 10:56 PM   #3
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Default Re: Samsung UN55JU7500F

Hi Budm,

Thanks for reply. Pfc voltage stays 391v if main board is disconnected. PS on is jumping between 3.3V to 0.09V when are boards are in place. I'll attach photo of the entire back of the tv.

Last edited by anupkg1985; 02-20-2021 at 11:08 PM..
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Old 02-21-2021, 11:17 AM   #4
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Default Re: Samsung UN55JU7500F

Back side of the tv with all boards connected. I have removed the heat sink on main board. It also has a one connect box separately.
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Last edited by anupkg1985; 02-21-2021 at 11:32 AM..
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Old 02-21-2021, 03:50 PM   #5
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Default Re: Samsung UN55JU7500F

Also noticed that 12.82V jumping to 9.2V and back may due to pfc on and off. Also there 3.2V present on FAIL_COUNT pin of the smps board. If I disconnect the main board then FAIL_COUNT voltage drops to 0.7v
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Old 02-22-2021, 04:52 PM   #6
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Default Re: Samsung UN55JU7500F

Anyone to help on this?
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Old 02-22-2021, 07:53 PM   #7
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Default Re: Samsung UN55JU7500F

If the standby voltages are stable and PS-ON signal is stable, main board is suspect if TV doesn't turn on.
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Old 02-22-2021, 11:02 PM   #8
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Default Re: Samsung UN55JU7500F

While main board is disconnected, shorting PS_ON pin with GND makes the backlight to turn off and pfc voltage goes down to 168V also other voltages drops. Does that indicates something wrong with PS?
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Old 02-22-2021, 11:06 PM   #9
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Default Re: Samsung UN55JU7500F

Quote:
Originally Posted by anupkg1985 View Post
While main board is disconnected, shorting PS_ON pin with GND makes the backlight to turn off and pfc voltage goes down to 168V also other voltages drops. Does that indicates something wrong with PS?
PS_ON is active high with a pull up resistor. Shorting it turns it off.
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Old 02-23-2021, 08:31 PM   #10
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Default Re: Samsung UN55JU7500F

So if it turns off then I should be getting 0v on 13v pin however it just drops to 9.2V. Also there would be some buzzing noise when I short PS-ON pin. Not sure if its really mainboard or ps itself. Could someone help to diagnose mainboard as well.
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Old 02-23-2021, 08:33 PM   #11
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Default Re: Samsung UN55JU7500F

I believe 9.2V is the standby voltage and gets boosted to 13V when turned on. Power supply is behaving as expected.
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Old 02-23-2021, 10:41 PM   #12
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Default Re: Samsung UN55JU7500F

Posting more findings -
1. Getting fluctuating voltage from 0.6V to 3.6V on SW_POWER test point near IC 301 which I believe is an eeprom (part number S24C51) hence the VCC of IC is also fluctuating. However if I remove PS_ON pin on the connector keeping other pins connected, voltage is stable 3.6V to eeprom vcc.

2. Also found the PIN#10 of IC1505_RS (part number MP221EC) connected to PS_ON pin on the connector, which is also fluctuating.

Can someone help to figure out or isolate the issue on the main board? I'm not able to find the mainboard replacement on shopjimmy or ebay, also whatever is available is very costly above 100 bucks.
Attached Images
File Type: jpg S24C51.jpg (566.3 KB, 9 views)
File Type: jpg MP221EC.jpg (2.04 MB, 5 views)

Last edited by anupkg1985; 02-23-2021 at 10:51 PM.. Reason: Update
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Old 02-24-2021, 07:10 AM   #13
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Default Re: Samsung UN55JU7500F

It looks like two of those IC legs (5 & 6) are soldered together. (S24C51.jpg (1 of 2))
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Old 02-24-2021, 08:43 AM   #14
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Default Re: Samsung UN55JU7500F

No its not, I was trying to reset it using shorting sda pin to GND however no luck. But those two pins are not shorted together.
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Old 02-24-2021, 11:38 PM   #15
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Default Re: Samsung UN55JU7500F

Could someone provide the schematics or troubleshooting guide for Samsung BN94-10098A Main Board?
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