EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: Miles Teg on January 05, 2023, 10:18:29 pm
-
Hello,
Got another subject today. An emergency for a family tv.
I get so few times before buying a new mother board for it ( 150€) and try to make good learnings.
So this Samsung TV is no more starting at all.
After some measures, the Power board seems ok.
And when unplugging the mother board, backlight switch ON correctly and 13V output for motherboard is ok.
I take back the mother board at home (65" frame remains in sister's house ::) )
I did my homeworks and check all power rails impedance to ground then plugged a 13V power bench on it.
Here is the result : KantM low.JPG
Hi-res here to download: https://drive.google.com/file/d/1bOXTxlMwqRuyY5Ntaos-3RGNDh5NTcru/view?usp=sharing (https://drive.google.com/file/d/1bOXTxlMwqRuyY5Ntaos-3RGNDh5NTcru/view?usp=sharing)
Current remains not measurable, so no obvious short circuit.
13V seems not reaching the main PMIC (Main PMICr.jpg) (Q209, Q211 Mosfet blocking)
MainPMIC (VPM1RT 4GQ41CN)
only one output capacitor impedance is concerning, but maybe that's on a negative rail. don't know.
13V reach top right regulator and provide correctly 5V and 3.3V.
5V goes on another regulator and provides 1.8V
These 3 rails reach the T296 chip aside the the eMMC, but nothing pass through
2 other regulators are on the left of processor. Supplied with the left entry mosfet on the supply connector
One of the cap bank as only 10 Ohm to the ground.
VCC input of EEPROM (3.3v) has 1.5K to ground.
1.8V reach correctly the power button. And drop to 0V when power button is activated. But no reaction on board, no led. And no change on power supply current output.
1: Fail Count 2: ANA-DIM
3: A13V 4: OD ON/OFF
5: A13V 6: BLU_PWM
7: A13V 8 : Power ON/OFF
9: A13V 10: GND
11: GND 12 : GND
An interesting video of a similar boad diagnosis on power supply (here a short on processor)
https://www.youtube.com/watch?v=ewJ1Li0Al9k (https://www.youtube.com/watch?v=ewJ1Li0Al9k)
Have you any advice of something to check?
Thank you.
-
I would try to determine where the enables for each of the LDOs and switchmode converters are coming from, and then construct some sort of power sequence block diagram.
The PMIC appears to have been manufactured by Silergy. Silergy's marking codes are either ABCxyx or ABxyz, where AB/ABC = alpha part ID, x = numeric year, y = week, z = lot number.
For example, IC201 = SY8286A.
SY8286A, Silergy, 6A, 23V Input Synchronous Step Down Regulator, 600kHz, 4V - 23Vin, marking AWRxyz, QFN3×3-20:
https://www.silergy.com/cn/download/downloadFile?id=3866&type=product&ftype=note (https://www.silergy.com/cn/download/downloadFile?id=3866&type=product&ftype=note)
The code for the PMIC would be VPMxyz.
Did you check the two crystals? Can you locate the reset pin for the SoC?
"T296" appears to be a dual load switch. The corner pins would be the inputs and outputs.
I suspect T296 is something like this:
http://www.aosmd.com/res/data_sheets/aoz1331di.pdf (http://www.aosmd.com/res/data_sheets/aoz1331di.pdf)
-
ISTM that the 0 ohm output of the PMIC warrants closer examination. As you say, it could be a negative supply, in which case the anode of the adjacent diode would be the -Vout.
It's difficult to recognise the topology of the "MR" output, but I'm wondering if it could be a boost converter. If so, then the cathode of the adjacent diode would be the +Vout.
Would these supplies be VGH and VGL?
The heaviest supply with the largest inductor (plus MOSFET and SSM54R diode) appears to be another boost converter. It appears to provide 17V for AVDD. The cathode of the diode would be the output.
I'm wondering which of the supplies is the SoC's Vcore. The resistance of the core would be less than 100 ohms. Could that explain the 10R and 33R readings? Could the SoC have two cores?
-
Here is a service manual for a different Samsung TV, but the connector pinouts on page 100 may turn out to be useful.
https://www.manualslib.com/download/2172781/Samsung-Ue49nu7172u.html (https://www.manualslib.com/download/2172781/Samsung-Ue49nu7172u.html)
One could use the 96-pin panel connector pinouts to discover the functions of each of the DC-DC converters. For example, to locate the AVDD_17V_PW converter, perform a continuity check between panel pin CN1300-94 and the AVDD test point which we previously identified.
There are several other supplies going to the panel, and these are probably generated by the PMIC. VOFF_-11V_PW and VGHD_30V_PW could be the VGH and "VGL" suspects discussed earlier.
The "T296" part is actually a "2897" (the second line).
This parts list (for a different model) identifies it as "IC-SWITCH; G2897KD1U, TDFN2X3-14, 14P, 2x3mm":
https://f01.justanswer.com/Electrotech2017/f0498489-136c-4693-a454-6cb8afded404_ANNEX_EV-UN58MU6100FXZA-DA01.pdf (https://f01.justanswer.com/Electrotech2017/f0498489-136c-4693-a454-6cb8afded404_ANNEX_EV-UN58MU6100FXZA-DA01.pdf)
I suspect it is made by Global Mixed-mode Technology, but I can't find a datasheet.
http://www.gmt.com.tw/product/SearchPN.php (http://www.gmt.com.tw/product/SearchPN.php)
-
Thank you @fzabkar !
All are good informations.
Yesterday I was investigating more the connections between chips, but still not a clear view. And no view to any problem.
I've identified 3 lines of main mosfet and the SW_Power_Delay, but all are going to the SoC.
I will post later today more details of my progress.
About your last post and documents, they can be really usefull as they seems related to the kant-M board which we can found on several samsung models but we some different options cabled on.
See you
-
I don't have much experience with flat panel TVs (my experience is with CRT TVs), but I've examined a few cheaper TVs with SoCs. In those cases the SoC had a small keep-alive section of silicon which was dedicated to monitoring the IR sensor and pushbuttons. I don't think there is much you can do other than to confirm the standby supply, reset and oscillator.