Samsung UE49KS7000SXXH - No standby light

[B0r1s]

Hi, my tv turned itself off and since than i can't turn it on. I have no standby light.

I tried like i saw on few youtube videos to disconnect the cable that is coming from the main board and than to power on tv, to see if backlight will appear, it did appear but only for a second, and while power cable was attached I noticed small ticking sound from the middle of power board. Than i attached the main board cable again and ticking sound was still present. I guess sound is coming from transformer area, but not sure.

Then i measured stby voltage on the board, and it is below normal value displayed on the board, and it is not stable (4v-5.7v), i got it on the video, when i detach main board cable values are a bit higher (5v-7.5v).

I looked for swollen or leaked caps but didnt found any. What do you think? what should i look for next?

Videos:

1. Ticking sound
https://www.veed.io/view/7aedcdf4-ba...ingWidget=true

2. Standby voltage
https://www.veed.io/view/ab30c28b-6b...ingWidget=true

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

maybe unplug the cable from powerboard to mainboard and the backlight cable, plug the power cord in and see if you get a steady standby voltage then.

[dskall]

Re: Samsung UE49KS7000SXXH - No standby light

I would check output diodes.

[B0r1s]

Re: Samsung UE49KS7000SXXH - No standby light

maybe unplug the cable from powerboard to mainboard and the backlight cable, plug the power cord in and see if you get a steady standby voltage then.

Just tried, same unstable stby voltage

I would check output diodes.

Which diodes are output ones on board?

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

go ahead and check all the diodes on top of board, do the round ones first.

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

they will have the stripe at one end, the others that resemble diodes without the stripe are ferrite beads not diodes. Meter set to diode put probe on each end, then switch probes, one way should read ol, other should read .5 or so.

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

looks like you have 4 others on the heatsinks, probably will check like this video, when in doubt look up the datasheet: https://www.youtube.com/watch?v=1KVBZSTY7FE

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

so maybe check dm851c, dm852c, dm853c and those 3 caps cm854, cm856, cm857.

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

a good clear picture like the one above but of the underside of board might help.

[B0r1s]

Re: Samsung UE49KS7000SXXH - No standby light

go ahead and check all the diodes on top of board, do the round ones first.

I checked following diodes with 20K ohm settings.


4 big round ones:

DM862C - .004 and .004 both directions.
DM864C - .004 and .004 both directions.
DM863C - 1.679 in correct direction and 1 in opposite.
DM861C - 1.679 in correct direction and 1 in opposite.

DM851C, DM852C, DM853C:

negative lead on middle leg, positive on other legs: .484
positive lead on middle leg, negative on other legs: 1
Positive lead on first leg and negative on third leg and vice versa: .004

I measured this while board was detached from tv frame.

Diode problem? But which one?

[Diah]

Re: Samsung UE49KS7000SXXH - No standby light

put your power boards alone on the table with out any socket connect to it only the wall socket power it on and messure yours STB V.

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

I checked following diodes with 20K ohm settings.


4 big round ones:

DM862C - .004 and .004 both directions.
DM864C - .004 and .004 both directions.
DM863C - 1.679 in correct direction and 1 in opposite.
DM861C - 1.679 in correct direction and 1 in opposite.

DM851C, DM852C, DM853C:

negative lead on middle leg, positive on other legs: .484
positive lead on middle leg, negative on other legs: 1
Positive lead on first leg and negative on third leg and vice versa: .004

I measured this while board was detached from tv frame.

Diode problem? But which one?

go ahead and recheck those but use diode mode.

[Diah]

Re: Samsung UE49KS7000SXXH - No standby light

his Post#1 99.9% er hat shorted LED BL

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

could very well be but why no steady standby on powerboard?

[Diah]

Re: Samsung UE49KS7000SXXH - No standby light

could very well be but why no steady standby on powerboard?

because bl socket in place .. pcb keep click.. if it has tongue he will hear Helllllppppp

[B0r1s]

Re: Samsung UE49KS7000SXXH - No standby light

because bl socket in place .. pcb keep click.. if it has tongue he will hear Helllllppppp

I measured stby voltage with disconnected backlight socket like nomoresonys told me, and stby was still unstable.. i will try in few hours to test power board detached from tv frame with only power cable attached like you said so..

[B0r1s]

Re: Samsung UE49KS7000SXXH - No standby light

go ahead and recheck those but use diode mode.

Ok i rechecked these diodes with diode mode. I have these two multimeters at the moment, and measurements are different on each one. I don't know which one to trust.

Multimeter MT111:

DM862C - on each measurement multimeter is changing settings from diode mode to ohm resistance and i get values - 0 ohms.
DM864C - same like with DM862C
DM863C - red lead on anode, black on cathode - 0.284 / when i switch leads - 0.794
DM861C - same like with DM863C

DM851C, DM852C, DM853C:

negative lead on middle leg, positive on other legs: 0.125
positive lead on middle leg, negative on other legs: values are dancing between 0.630-0.700
Positive lead on first leg and negative on third leg and vice versa: it's switching to ohm resistance - 0 ohms

Multimeter DT-830B:

DM862C - 003 both directions
DM864C - 003 both directions
DM863C - 288 in correct direction and 1 in opposite
DM861C - 288 in correct direction and 1 in opposite

DM851C, DM852C, DM853C:

negative lead on middle leg, positive on other legs: 129
positive lead on middle leg, negative on other legs: 1
Positive lead on first leg and negative on third leg and vice versa: 002


Also i measured voltage while board was detached from tv, with only power socket connected, same unstable voltage.

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

DM862C - 003 both directions
DM864C - 003 both directions: it looks like one or both of these is/are shorted, take one out of circuit and recheck it, if ok or bad recheck the other one in circuit to see if it's ok or not, maybe only one is bad.

[B0r1s]

Re: Samsung UE49KS7000SXXH - No standby light

Sorry for delay. I ordered quicko t12-942 from china, and I'm waiting for it to arrive. In the meantime i bought electric desoldering pump and took out two diodes, and yes one is shorted.

On the diodes it is printed:

LT6 | 23
SB5 | 50

Searching trough google i figured out that this is sb 550 schottky diode. I only found sb 560 diodes to buy.

While testing sb 550 and sb 560 diodes out of circuit i get different readings in diode mode:

SB550: 0.350
SB560: 0.195

So can i replace diodes with the new ones?

[nomoresonys]

Re: Samsung UE49KS7000SXXH - No standby light

I think you're good to go, maybe replace all 4 so they are the same, hope you got more than 2.