Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

[DXseekerMO]

Hi everyone, today I'm working on this Samsung UN55F6300AFXZA. The stand-by light is not illuminating and the TV appears outwardly unresponsive. I tested voltages first with the MB hooked up to the PS then unhooked. The backlights all come on when the MB is unhooked from the PSU and all the voltages appear to come up to at or very close to what is on the board.

Here are the voltage readings:

Pin no/descr…………………..V w MB plugged in………….. V with MB unplugged

1 B13V………………………….. 0………………………………………12.67
2 P_DIM…………………………0 ……………………………………...12.67
3 B13V……………………………0………………………………………12.67
4 NC
5 Vamp…..………………………0 ………………………………………12.67
6 BLU_ON…………………….…0 ………………………………………2.98
7 Vamp…………………………..0 ………………………………………12.67
8 GND…………………verified to chassis
9 GND………………… “ “ “
10 GND………………. “ “ “
11 B5V…………………………….0 ………………………………………5.3
12 A5V…………………………….5.29………………………………….5.3
13 B5V…………………………….0 ………………………………………5.3
14 PS_on……………………… 0.24 …………………………………3.31

I suspect the main board is where the problem lies, so I traced the stand-by pin on the main board to IC1201 which is Weltrend Flat Panel Display Control Sub-MCU 61P8-RG480WT(LQFP), in particular to pin 22 (DSDA1) where 5V is present.

CN1201 is the connector from the P-JOG switch and wi-fi module. PIN 11 of CN1201 appears to be the high/low circuit for the power button. There are about .27v present at pin 11 until the power button is activated and the voltage drops to zero until the power button is released.

Furthermore I traced the PS_on pin to IC208 which is an AlphaOmega AOZ3018PI, 5A synchronous buck regulator. The PS_on pin traces through a couple resistors in series which appear to be working, about 4800ohms through both. From the last resistor in-series I get continuity direct to pins 2 (Vin), 3 (AGND) and 8 LX(sense) pins. There is no voltage present on any of its pins.

I traced this down as far as I think I can for the present, so I'm hoping for some guidance from here.

[budm]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

The power supply board has pull-up resistors for doing the self-test, right no the min board is keeping the PS-ON lo so the rest of the power supply will not come on.
The PS-ON line will usually go to the Collector of the Switched Transistor, the Transistor will be normally on to keep the PS-ON line LO, When TV is turned on then the Transistor will turn off to allow the PS-ON to go HI.
Since you have so many missing control lines (PS-ON, DIM, BLU-ON) so you have more problem than just PS-ON problem.

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

The power supply board has pull-up resistors for doing the self-test, right no the min board is keeping the PS-ON lo so the rest of the power supply will not come on.
The PS-ON line will usually go to the Collector of the Switched Transistor, the Transistor will be normally on to keep the PS-ON line LO, When TV is turned on then the Transistor will turn off to allow the PS-ON to go HI.
Since you have so many missing control lines (PS-ON, DIM, BLU-ON) so you have more problem than just PS-ON problem.

So with it narrowed down to the main board should I start back-tracing all of these missing control lines to see if there's something in-common that has failed? Where would you suggest I proceed from here?

[Unspun01]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

IC201 and IC204 and IC208 all appear to be some type of voltage regulators since they are each connected to an adjacent coil (L201, L202, L203 respectively)

Identify IC201, IC204, IC208 and obtain pinouts from their datasheets. Test for missing voltages, or specifically shorts to ground on any pin that shouldn't be grounded.

Test to make sure none of the coils are shorted to ground.

Test for shorts across many smt capacitors. If you find any smt caps with low ohms or direct shorts, test nearby ICs or transistors.

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

IC201 and IC204 and IC208 all appear to be some type of voltage regulators since they are each connected to an adjacent coil (L201, L202, L203 respectively)

Identify IC201, IC204, IC208 and obtain pinouts from their datasheets. Test for missing voltages, or specifically shorts to ground on any pin that shouldn't be grounded.

Test to make sure none of the coils are shorted to ground.

Test for shorts across many smt capacitors. If you find any smt caps with low ohms or direct shorts, test nearby ICs or transistors.

Thanks for the reply. I tested all of those IC's you listed just now but I didn't pull the datasheets. There is little to no voltage present at any of them. One leg of the main EEPROM had .9V

The only major voltage I seem to be able to find is the 5.28V stand-by voltage on pin 22 of IC1201. I traced the stand-by circuit very carefully and the only place I see the trace going to is directly to IC1201. I don't see any other branches off this line.

From IC1201 on there is no voltage that I can see. I'm not sure of which pins, if any allow power through it for other things in the stand-by circuit? Just guessing IC1201 has to allow current to pass to power other items in the stand-by circuit?

EDIT/ADD: The rest of the board appears dead, I checked several transistors, other items and find little (.2V) to no voltage.

[Unspun01]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

Without pulling the datasheets for some of the regulators and ICs you are shooting in the dark.

Do yourself a favor and find the datasheets to determine which pins are inputs, and which pins are outputs. If you cannot confirm input voltage to any of these regulators, you cannot hope to measure outputs.

I checked several transistors, other items and find little (.2V) to no voltage.

As I stated, don't worry so much about correct voltages. Focus your attention on seeing if there are any shorts to ground.

Every single surface mount capacitor is important to troubleshoot this way.

Set your multimeter to continuity mode. Hopefully it beeps when leads are touching each other.

Securely attach the black probe of your multimeter to any metal part or screw on the TV chassis to provide a good ground.

With the red multimeter probe touch both ends of every single surface mount capacitor on the main board.

If you find any surface mount caps that beep (or measure low ohms) on both sides, then you know that a voltage or trace connected to that cap is suspect.

You can place a dot on the cap with a permanent marker and come back to it later. You may find several on the same supply line that measure shorted. Then concentrate on the regulators and ICs.

I often find bad ICs or components by testing nearby caps.

You may not find any issues if there are no shorts, but it's the first place I always start.

[nomoresonys]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

Without pulling the datasheets for some of the regulators and ICs you are shooting in the dark.

Do yourself a favor and find the datasheets to determine which pins are inputs, and which pins are outputs. If you cannot confirm input voltage to any of these regulators, you cannot hope to measure outputs.



As I stated, don't worry so much about correct voltages. Focus your attention on seeing if there are any shorts to ground.

Every single surface mount capacitor is important to troubleshoot this way.

Set your multimeter to continuity mode. Hopefully it beeps when leads are touching each other.

Securely attach the black probe of your multimeter to any metal part or screw on the TV chassis to provide a good ground.

With the red multimeter probe touch both ends of every single surface mount capacitor on the main board.

If you find any surface mount caps that beep (or measure low ohms) on both sides, then you know that a voltage or trace connected to that cap is suspect.

You can place a dot on the cap with a permanent marker and come back to it later. You may find several on the same supply line that measure shorted. Then concentrate on the regulators and ICs.

I often find bad ICs or components by testing nearby caps.

You may not find any issues if there are no shorts, but it's the first place I always start.

+10 Very good advice.

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

Without pulling the datasheets for some of the regulators and ICs you are shooting in the dark.

Do yourself a favor and find the datasheets to determine which pins are inputs, and which pins are outputs. If you cannot confirm input voltage to any of these regulators, you cannot hope to measure outputs.



As I stated, don't worry so much about correct voltages. Focus your attention on seeing if there are any shorts to ground.

Every single surface mount capacitor is important to troubleshoot this way.

Set your multimeter to continuity mode. Hopefully it beeps when leads are touching each other.

Securely attach the black probe of your multimeter to any metal part or screw on the TV chassis to provide a good ground.

With the red multimeter probe touch both ends of every single surface mount capacitor on the main board.

If you find any surface mount caps that beep (or measure low ohms) on both sides, then you know that a voltage or trace connected to that cap is suspect.

You can place a dot on the cap with a permanent marker and come back to it later. You may find several on the same supply line that measure shorted. Then concentrate on the regulators and ICs.

I often find bad ICs or components by testing nearby caps.

You may not find any issues if there are no shorts, but it's the first place I always start.

Ok, I haven't tried to pull any datasheets yet, but I did measure for short on all the caps on the board. I found a short here and there, but mainly by components that I think would cause them to read short (like an inductor, etc), but when I got to a group directly under the processor and right above the Ethernet port nearly every single one reads short to ground on both sides of the cap, chassis ground is referenced. Pictures are attached, some are not marked with a marker.

+10 Very good advice.

Indeed, now to pull some datasheets...

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

Datasheets pulled. Vin (DC supply voltages) are missing on all of them.

Main EEPROM voltage in is 1.15V.

The 3.3V pin on IC1201 reads zero.

It looks like all of these run to the processor. That in combination with all the caps under it that indicate short is making it look like the processor is shorted out.

It's not looking good for this main board best I can see.

[budm]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

Btw, did you try disconnecting the WIFI module?

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

Btw, did you try disconnecting the WIFI module?

No, sure didn't. Are they problematic on these?

[budm]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

It can cause the MB to hang up.

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

It can cause the MB to hang up.

Gotcha! I believe I'll give that a try. Worth a shot for sure!

[budm]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

BTW, those 3-pin devices (3 of them) with big metal with center pin trimmed off, can you read P/N and Voltages on all 3 pins?

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

It can cause the MB to hang up.

Unfortunately there's no change. Still appeared dead with Wi-Fi module unhooked..

[budm]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

See post 16.

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

See post 16.

Missed that lol, I'll re-check tomorrow.

[Dannyx]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

Almost certain dead CPU, having worked with Sammies for several years now. When they don't have standby, I almost always stop right there and look for a replacement board. I've been fairly unlucky in doing component-level repairs on them. You might get lucky, who knows, that's why I'm dropping by here - curious to see what the verdict is.

Another way to identify where the short is is to use a variable power supply hooked up between GND and the part which reads shorted and SLOWLY increase the voltage and observe the current and feel for any parts heating up - useful for identifying shorted caps. Of course, care must be taken not to exceed the nominal voltage of that rail, so if it's a 3.3v rail, your supply mustn't go higher than that. If it's the CPU for instance, the supply rail is going to be very low 1-2v max, so even if shorted it might not pull enough current to heat up anything, or at least not enough to feel it, making the job harder...hope it's not too confusing. Basically you deliberately apply power to the short to cause it to heat up so you can see which it is....Louis Rossmann does this extensively on his laptops.

[Unspun01]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

DXseekerMO:

I just remembered another repair I did for a 58" Samsung LED TV.

In your first post, you said that the backlights come on when the mainboard is disconnected from the power supply (TV plugged in of course).

I had same issue: my backlights stay on when power cable to mainboard is disconnected. I suspected bad mainboard, or bad 13V regulation on PSU…

Problem WAS mainboard - replaced 3A regulator AOZ3013PI 8-pin SOIC chip. The regulator did not measure any shorts, but was bad. I scavenged a Z3013PI from a 65" Samsung mainboard and it works great.

You have a Z3013 or Z3018 (I can't read from the photos) on your mainboard. You may want to see if swapping one of these regulators from another board will work.

[DXseekerMO]

Re: Samsung UN55F6300AFXZA appears dead, stand-by present, main board suspect

DXseekerMO:

I just remembered another repair I did for a 58" Samsung LED TV.

In your first post, you said that the backlights come on when the mainboard is disconnected from the power supply (TV plugged in of course).

I had same issue: my backlights stay on when power cable to mainboard is disconnected. I suspected bad mainboard, or bad 13V regulation on PSU…

Problem WAS mainboard - replaced 3A regulator AOZ3013PI 8-pin SOIC chip. The regulator did not measure any shorts, but was bad. I scavenged a Z3013PI from a 65" Samsung mainboard and it works great.

You have a Z3013 or Z3018 (I can't read from the photos) on your mainboard. You may want to see if swapping one of these regulators from another board will work.

It is a Z3018.