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Old 02-03-2022, 05:06 PM   #41
R_J
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Default Re: Samsung UN55EH6000F Power issue

But what else did they damage when they went bad? usually components in the gate circuit get damaged as well, Also have a look at CL802 (blue cap) does it look bulged at all?
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Old 02-03-2022, 05:09 PM   #42
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Default Re: Samsung UN55EH6000F Power issue

Pulled all caps and tested with ESR meter and were almost spot on. No bulging either. I had to also replace RL820 was open and also replaced the zener diode ZDL802 was also open.
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Old 02-03-2022, 05:15 PM   #43
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Default Re: Samsung UN55EH6000F Power issue

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The resistor is ok. That is the source resistor for the pfc mosfet.
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Pulled all caps and tested with ESR meter and were almost spot on. No bulging either. I had to also replace RL820 was open and also replaced the zener diode ZDL802 was also open.
If ZD802 went open, I suspect RL822 could be open as well, and if both mosfets were shorted, I would change ZDL801 as well.
If any components in the gate drive are not correct, the circuit will not switch properly and draw too much current.
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Old 02-03-2022, 05:20 PM   #44
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Default Re: Samsung UN55EH6000F Power issue

RL822 checks ok and I did replace ZDL801 at the same time as other one. Thank you R_J for your time as it's much appreciated. I need to quit for the day but if you think of something please let me know and I will check it in the morning and report back ASAP.
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Old 02-04-2022, 11:43 AM   #45
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Default Re: Samsung UN55EH6000F Power issue

R_J I was thinking that when I checked voltage at the big cap it was also fluctuating so would still be a problem on the hot side of the board. Would the rectifier have anything to do with it???
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Old 02-04-2022, 11:54 AM   #46
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Default Re: Samsung UN55EH6000F Power issue

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R_J I was thinking that when I checked voltage at the big cap it was also fluctuating so would still be a problem on the hot side of the board. Would the rectifier have anything to do with it???
explain Fluctuating, Fluctuating from 385v to ???
What rectifier? there are lots of them on the board, and they all have board identifiers

If QL801 & QL802 are not switching properly, they will likely cause the main pfc boosted voltage to drop. but it should not drop all the way down from 385 to 160v

Last edited by R_J; 02-04-2022 at 12:04 PM..
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Old 02-04-2022, 12:09 PM   #47
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Default Re: Samsung UN55EH6000F Power issue

Well it happened so fast and was never a steady voltage on the big cap. I think I seen 380v then down to 100 something but was very fast. I was asking about BD801S I think it is. Would you think I just try replacing QL801 and QL802 again? In case I got some bad new ones??
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Old 02-04-2022, 12:27 PM   #48
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Default Re: Samsung UN55EH6000F Power issue

The main supply should not drop below 165vdc, I can see the pfc circuit shutting down and the voltage dropping from 385v to 165v
The mosfets may have been damaged if they were replaced before the gate resistor and zener were replaced.
BD801s is the main bridge rectifier, I doubt it is bad, none of the 4 diodes are shorted or it would blow the main fuse and it is unusual for one of the diodes to o open.

The whole board seems to be working except for the backlight supply circuit, and when the backlight circuit is working it should supply 331V at 289ma which is not that much of a draw on the main supply, and with no led's connected (unloaded)it should not be drawing much current at all.

Last edited by R_J; 02-04-2022 at 12:45 PM..
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Old 02-04-2022, 12:46 PM   #49
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Default Re: Samsung UN55EH6000F Power issue

Replaced them both again and still no joy. Here is a pic of old one on left and new on right.
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File Type: bmp 0001.bmp (1.60 MB, 5 views)
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