Samsung UN55EH6000F Power issue

[CraigR]

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.

[R_J]

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.

[CraigR]

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??

[R_J]

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???

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

[CraigR]

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???

[CraigR]

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.

[R_J]

Re: Samsung UN55EH6000F Power issue

The resistor is ok. That is the source resistor for the pfc mosfet.

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.

[CraigR]

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.

[R_J]

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?

[CraigR]

Re: Samsung UN55EH6000F Power issue

QL801 and QL802 are new.

[R_J]

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.

[CraigR]

Re: Samsung UN55EH6000F Power issue

from 54v to 11v constant fluctuation.

[R_J]

Re: Samsung UN55EH6000F Power issue

Yes, when you say you get voltage up and down can you give a number?

[CraigR]

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?

[R_J]

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.

[CraigR]

Re: Samsung UN55EH6000F Power issue

Just pulled them and checked with component tester and good.

[R_J]

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.

[CraigR]

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

They do! they stay normal now.

[R_J]

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?

[CraigR]

Re: Samsung UN55EH6000F Power issue

Ok, so now what can I check?