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Old 02-03-2022, 02:17 PM   #21
R_J
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Default Re: Samsung UN55EH6000F Power issue

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Originally Posted by CraigR View Post
Zero volts 5 nor 13 when when PS_ON/OFF jumped to ground.
You will not get B5V or B13V but you should get A5V (JP809) with the board turned off
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Old 02-03-2022, 02:32 PM   #22
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Default Re: Samsung UN55EH6000F Power issue

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You will not get B5V or B13V but you should get A5V (JP809) with the board turned off
Ok, yes I get 5v on JP809 with it jumped.
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Old 02-03-2022, 02:43 PM   #23
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Default Re: Samsung UN55EH6000F Power issue

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Ok, yes I get 5v on JP809 with it jumped.
when you remove the jumper does the A5V stay at 5volts? or does it drop? If it drops I suspect the standby circuit is not supplying enough voltage to keep itself and the pfc circuit working.

Last edited by R_J; 02-03-2022 at 02:47 PM..
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Old 02-03-2022, 02:51 PM   #24
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Default Re: Samsung UN55EH6000F Power issue

Yes, it stays at 5v
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Old 02-03-2022, 02:59 PM   #25
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Default Re: Samsung UN55EH6000F Power issue

I'm now just guessing at things and tested this resistor RP820 and out of circuit it's 0.11 but I can not find a chart online that the colors work with. Under the scope it looks black, gold, black, gray, black. but this comes as an error on the calculators.
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Old 02-03-2022, 03:00 PM   #26
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Default Re: Samsung UN55EH6000F Power issue

with power supply on, Check the voltage across the main filter capacitor CP806

This voltage should be around 165vdc in standby and go to around 300vdc when the power supply is on.
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Old 02-03-2022, 03:02 PM   #27
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Default Re: Samsung UN55EH6000F Power issue

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I'm now just guessing at things and tested this resistor RP820 and out of circuit it's 0.11 but I can not find a chart online that the colors work with. Under the scope it looks black, gold, black, gray, black. but this comes as an error on the calculators.
The resistor is ok. That is the source resistor for the pfc mosfet.
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Old 02-03-2022, 03:08 PM   #28
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Default Re: Samsung UN55EH6000F Power issue

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with power supply on, Check the voltage across the main filter capacitor CP806

This voltage should be around 165vdc in standby and go to around 300vdc when the power supply is on.
172v in standby and 386v on.
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Old 02-03-2022, 03:20 PM   #29
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Default Re: Samsung UN55EH6000F Power issue

If the PFC voltage 386vdc is steady, that means the standby circuit and the pFC circuit are working as they should.
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Old 02-03-2022, 03:23 PM   #30
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Default Re: Samsung UN55EH6000F Power issue

Ok, so now what can I check?
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Old 02-03-2022, 03:37 PM   #31
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Default Re: Samsung UN55EH6000F Power issue

I don't have a schematic, I am using the pictures of the board. I would try grounding the BLU_ON/OFF pin CNM803 pin6 and see if the B5v and B13v stay up

It might be that the backlight drive circuit is killing the B13v?

Last edited by R_J; 02-03-2022 at 03:45 PM..
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Old 02-03-2022, 03:45 PM   #32
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Default Re: Samsung UN55EH6000F Power issue

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I don't have a schematic, I am using the pictures of the board. I would try grounding the BLU_ON/OFF pin CNM803 pin6 and see if the B5v and B13v stay up
They do! they stay normal now.
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Old 02-03-2022, 04:01 PM   #33
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Default Re: Samsung UN55EH6000F Power issue

So when the backlight circuit is turned on there is too much load on the supply, Back to post 1 where the two mosfets were replaced, It could be that they are being turned on hard and killing the supply. There are also a pair of dual diodes, DL851 & DL852, I would check them as well

This is a guess but it might be caused by open led's in the panel and the board is shutting down due to an over voltage on the led supply.

Last edited by R_J; 02-03-2022 at 04:05 PM..
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Old 02-03-2022, 04:11 PM   #34
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Default Re: Samsung UN55EH6000F Power issue

Just pulled them and checked with component tester and good.
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Old 02-03-2022, 04:30 PM   #35
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Default Re: Samsung UN55EH6000F Power issue

What voltage do you get on JP840 when the backlight circuit is enabled (BLU_ON/OFF ground removed) Does it jump up to 300vdc? or is it higher? If it jumps up higher, connect the backlights and check the voltage again.
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Old 02-03-2022, 04:39 PM   #36
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Default Re: Samsung UN55EH6000F Power issue

On JP840 I get voltage up and down. but with BLU_ON/OFF jumped to ground I get no volt. Is that what you wanted to know?
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Old 02-03-2022, 04:52 PM   #37
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Default Re: Samsung UN55EH6000F Power issue

Yes, when you say you get voltage up and down can you give a number?
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Old 02-03-2022, 04:54 PM   #38
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Default Re: Samsung UN55EH6000F Power issue

from 54v to 11v constant fluctuation.
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Old 02-03-2022, 04:59 PM   #39
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Default Re: Samsung UN55EH6000F Power issue

That is way too low, I suspect there is still a problem with the mosfets QL801 & QL802 or there gate drive circuit.
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Old 02-03-2022, 05:01 PM   #40
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Default Re: Samsung UN55EH6000F Power issue

QL801 and QL802 are new.
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