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Old 08-05-2020, 03:29 PM   #1
greglogan
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Default Hisense UB50CE591

Hi guys

I've been scouring the site looking for info on the above set. Here is my problem. The set powers up and you can see the Hisense logo followed by Smart. It's dim, but it's there. After that, the screen goes dark. I've checked the voltages on both LED connectors. One seems to hover around 120V until the power supply shuts down. The other is around 400V and then shuts down too.
Are your suspicions LEDs or a power supply/driver issue?

Appreciate any help you guys can give

thanks

greg.
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Old 08-05-2020, 03:31 PM   #2
neilc6
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Default Re: Hisense UB50CE591

You are describing the symptoms of bad backlights. You are 10x more likely to have bad backlights then a bad power supply though bad backlights can damage power supplies.
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Old 08-05-2020, 03:31 PM   #3
Diah
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Default Re: Hisense UB50CE591

Quote:
Originally Posted by greglogan View Post
Hi guys

I've been scouring the site looking for info on the above set. Here is my problem. The set powers up and you can see the Hisense logo followed by Smart. It's dim, but it's there. After that, the screen goes dark. I've checked the voltages on both LED connectors. One seems to hover around 120V until the power supply shuts down. The other is around 400V and then shuts down too.
Are your suspicions LEDs or a power supply/driver issue?

Appreciate any help you guys can give

thanks

greg.
you have shorted ONE LED BL
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Old 08-05-2020, 03:39 PM   #4
budm
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Default Re: Hisense UB50CE591

Quote:
Originally Posted by greglogan View Post
Hi guys

I've been scouring the site looking for info on the above set. Here is my problem. The set powers up and you can see the Hisense logo followed by Smart. It's dim, but it's there. After that, the screen goes dark. I've checked the voltages on both LED connectors. One seems to hover around 120V until the power supply shuts down. The other is around 400V and then shuts down too.
Are your suspicions LEDs or a power supply/driver issue?

Appreciate any help you guys can give

thanks

greg.
Show us good clear pictures of the whole backside of the TV showing all the boards, and good clear straight shots picture of the power supply board.
Did you test the LED connector Voltage with ref to chassis GND?
400V reading means the LED power supply is not seeing the load, you have open circuit in the LED string.
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Old 08-05-2020, 03:54 PM   #5
greglogan
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Default Re: Hisense UB50CE591

Voltage tested across the PS outputs both times at XP901. It's strange because when I swap the connectors around, you can't see the logo on startup, so that's why I was thinking maybe Power Supply.

Pic of the PSB attached. Really appreciate your help.

Quote:
Originally Posted by budm View Post
Show us good clear pictures of the whole backside of the TV showing all the boards, and good clear straight shots picture of the power supply board.
Did you test the LED connector Voltage with ref to chassis GND?
400V reading means the LED power supply is not seeing the load, you have open circuit in the LED string.
Attached Images
File Type: jpg 20200805_225047[1].jpg (678.0 KB, 4 views)
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Old 08-05-2020, 03:55 PM   #6
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Default Re: Hisense UB50CE591

Do you think one shorted and one open on different strings as the voltage is different?

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you have shorted ONE LED BL
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Old 08-05-2020, 03:57 PM   #7
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Default Re: Hisense UB50CE591

Quote:
Originally Posted by greglogan View Post
Do you think one shorted and one open on different strings as the voltage is different?
NO, bl work as one circuit to shut down if one of them have issue
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Old 08-05-2020, 04:00 PM   #8
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Default Re: Hisense UB50CE591

I got this schematic from this site - it's not exactly the same, but it's pretty close. I thought the PS operated both LED strings separately, that's why i was getting different voltages.

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NO, bl work as one circuit to shut down if one of them have issue
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File Type: pdf RSAG7.820.5687_PS.pdf (57.6 KB, 5 views)

Last edited by greglogan; 08-05-2020 at 04:00 PM.. Reason: To add attachment
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Old 08-05-2020, 04:03 PM   #9
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Default Re: Hisense UB50CE591

Quote:
Originally Posted by greglogan View Post
I got this schematic from this site - it's not exactly the same, but it's pretty close. I thought the PS operated both LED strings separately, that's why i was getting different voltages.
you have SOS shutdown.. both sockets of BL share same IC to control the currents of them.
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Old 08-05-2020, 04:08 PM   #10
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Default Re: Hisense UB50CE591

Thank you so much. I'll get some LEDs ordered in the morning

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you have SOS shutdown.. both sockets of BL share same IC to control the currents of them.
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Old 08-05-2020, 04:10 PM   #11
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Default Re: Hisense UB50CE591

they are 3030 6V
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Old 08-05-2020, 04:22 PM   #12
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Default Re: Hisense UB50CE591

Quote:
Originally Posted by greglogan View Post
Voltage tested across the PS outputs both times at XP901. It's strange because when I swap the connectors around, you can't see the logo on startup, so that's why I was thinking maybe Power Supply.

Pic of the PSB attached. Really appreciate your help.
The LED drive Voltage is rated at 200V @400mA as printed right on the board, when no load the Voltage will jump high and trips the shutdown circuit.
So did you check the good LED in the Diode mode and tell us what you get in both directions?
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Old 08-06-2020, 04:17 AM   #13
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Default Re: Hisense UB50CE591

Thanks @Diah

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they are 3030 6V
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Old 08-06-2020, 04:18 AM   #14
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Default Re: Hisense UB50CE591

Hi

I hadn't spotted the voltage quoted, so thanks for that. I'm gonna tear down the rest of this evening and I will report after that.

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The LED drive Voltage is rated at 200V @400mA as printed right on the board, when no load the Voltage will jump high and trips the shutdown circuit.
So did you check the good LED in the Diode mode and tell us what you get in both directions?
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Old 08-06-2020, 09:04 AM   #15
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Default Re: Hisense UB50CE591

im doing battle with one of these ,
see my post from a few days ago same model no led supply volts
ive ordered backlight drive/controller ic lx27901
as it measures 160 ohm to deck on pin 16 its on the print side of the board,
i think when the leds fail they can damage this ic ,

so it might be worth you checking yours these ics are only a few quid each
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Old 08-06-2020, 09:09 AM   #16
greglogan
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Default Re: Hisense UB50CE591

Jim

can you measure that resistance in circuit or did you de-solder?
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Old 08-06-2020, 09:30 AM   #17
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Default Re: Hisense UB50CE591

Quote:
Originally Posted by greglogan View Post
Jim

can you measure that resistance in circuit or did you de-solder?
in situ is fine.
as theres only a cap on this pin which could be responsible .in my case
for me to confirm i de soldered just to be sure before i ordered ic
this pin when tv working normally should have 5v on it and mine had .9v
the 5v is generated inside the chip
if you source any suitable leds please let me know where from , so i can also get some
thanks

Last edited by jimbofz; 08-06-2020 at 09:33 AM..
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Old 08-06-2020, 10:32 AM   #18
Diah
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Default Re: Hisense UB50CE591

after take the defect LED need to take it in one piece so you can remark the chassis soldering pad of it. there are many 3030 but the pad are different.
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Old 08-07-2020, 07:32 AM   #19
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Default Re: Hisense UB50CE591

Quote:
Originally Posted by greglogan View Post
Jim

can you measure that resistance in circuit or did you de-solder?
hi did you measure pin 16 to deck?
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