Samsung 32" power supply BN44-0351B no backlight

[seve91]

Hi everyone,
got this TV with no backlight.
Soldered a 1k resistor between pin 16 and 18 of CNM801 and measured all the voltages.
Seems all ok, but in the drive block output i don't have high voltage for the backlight.
In fact the TV power on correctly, can hear the sound and can see that the panel is working if i put a torch in front of it.

How to troubleshoot the backlight? Thanks

[attainteddragon]

Re: Samsung 32" power supply BN44-0351B no backlight

pictures of the entire back of the tv and a pic of the ps, to start with.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

ok here you are:
http://imgur.com/fVgnZDS
http://imgur.com/fOE2XLH
http://imgur.com/aVTshVM

Model of the PSU is BN44-0351B

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

If you could add your pictures as attachments on the forum it makes it easier for people in the future to follow your repair.

Does pin 4 BLU_On/Off go high when switched out of standby. If it does then what voltages do you have on pins 1 to 16 of ICD801

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

ok i will repost the photos as attachment:





Actually i got a 1k resistor soldered between pins 16 and 18 of CNM801 to force POWER ON, and i get 2.9V on BLU_ON/OFF signal.

I will measure voltages of ICD801 and i will let you know...thanks!

[R_J]

Re: Samsung 32" power supply BN44-0351B no backlight

This is from elektrotanya.com

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

Here the voltages in DC between the PIN and GND:
1 - 0V
2 - 0.8V
3 - 0V
4 - 0V
5 - 0V
6 - 0V
7 - 0V
8 - 0V
9 - 0V
10 - 0V
11 - 0V
12 - 0V
13 - 5V
14 - 0V
15 - 1.02V
16 - 0V

I already have that schematic, but i don't know which voltages and which signals should i get in the circuits

[thoma]

Re: Samsung 32" power supply BN44-0351B no backlight

What is the correct name of your samsung lcd tv?

for example un32eh4003 we need the exact name of the TV!!!

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

You say in post #1

Soldered a 1k resistor between pin 16 and 18 of CNM801 and measured all the voltages. Seems all ok, but in the drive block output i don't have high voltage for the backlight. In fact the TV power on correctly, can hear the sound and can see that the panel is working if i put a torch in front of it.

But in your list above there is only one voltage shown?

There are also 18 pins (not 16) on that connector and the name of the pins 1 to 18 is given alongside the connector in a box with an arrow pointing to the connector. The connect pins are numbered with odd pin numbers on one side and even on the other.

If you could give the voltages along side the pin number and pin name would be more useful.

For example
Pin 1, GND, 0V
Pin 2, PWM, 1.2V

[thoma]

Re: Samsung 32" power supply BN44-0351B no backlight

http://www.teleservice-depannage.com...-UE32C5100.htm

you have to disconnect the cable between main and power if backlight appears
main defekt if not power defect samsung uses pull up resistance!!!!

http://www.toms-service-manuals.com/...typekey=0&p=16

see fast track guide take 40 inch

[CapLeaker]

Re: Samsung 32" power supply BN44-0351B no backlight

Hi everyone,
got this TV with no backlight.
Soldered a 1k resistor between pin 16 and 18 of CNM801 and measured all the voltages.
Seems all ok, but in the drive block output i don't have high voltage for the backlight.
In fact the TV power on correctly, can hear the sound and can see that the panel is working if i put a torch in front of it.

How to troubleshoot the backlight? Thanks

Actually you just need to unplug everything from the PSU, leave the backlights connected, plug in the PSU and the backlights should come on. These Samsungs have a pull up resistor built into the PSU.
However, lets say you have a PSU that doesn't have a pull up resistor built in, you need to put STBY voltage through a 1k resistor to PSon and BLon. If you just put power to PSon alone, it wont fire the backlights.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

What is the correct name of your samsung lcd tv?

for example un32eh4003 we need the exact name of the TV!!!

Correct model of LCD is UE32C5100QWXZT

You say in post #1 But in your list above there is only one voltage shown?

There are also 18 pins (not 16) on that connector and the name of the pins 1 to 18 is given alongside the connector in a box with an arrow pointing to the connector. The connect pins are numbered with odd pin numbers on one side and even on the other.

If you could give the voltages along side the pin number and pin name would be more useful.

For example
Pin 1, GND, 0V
Pin 2, PWM, 1.2V

You ask me to measure the voltages on IC ICD801, that has 16 pins, and these are the voltages:

1 - VCC - 0V
2 - ISET - 0.8V
3 - GATE - 0V
4 - GND - 0V
5 - CS - 0V
6 - AUTO - 0V
7 - RT - 0V
8 - SYNC - 0V
9 - CLIM - 0V
10 - REF - 0V
11 - PWMO - 0V
12 - OVP - 0V
13 - PWMI - 5V
14 - COMP - 0V
15 - FBP - 1.02V
16 - FBN - 0V

These are the voltages of the CNM801...i read on a post that i should put a 1k resistor between 16 and 18 to force power on, so i did it:

1 - D12V - 13V
2 - VDRV - 1.8V
3 - D12V - 13V
4 - BLU_ON_OFF - 2.9V
5 - D12V - 13V
6 - PWM_DIM - 5.126V
7 - GND - 0V
8 - NC - 0V
9 - GND - 0V
10 - GND - 0V
11 - D5.3V - 5.24V
12 - GND - 0V
13 - D5.3V - 5.24V
14 - D5.3V - 5.24V
15 - Vamp - 13V
16 - STBY_5.2V - 5.2V
17 - Vamp - 13V
18 - POWER_ON_OFF - 1.16V

http://www.teleservice-depannage.com...-UE32C5100.htm

you have to disconnect the cable between main and power if backlight appears
main defekt if not power defect samsung uses pull up resistance!!!!

http://www.toms-service-manuals.com/...typekey=0&p=16

see fast track guide take 40 inch

tried to disconnect the cable between motherboard and PSU but backlight doesn't appear...tried also to solder a 1k resistor between pin 16 and 4 to force backlight, without success.
I will look at fast track guide tonight, thanks.

Actually you just need to unplug everything from the PSU, leave the backlights connected, plug in the PSU and the backlights should come on. These Samsungs have a pull up resistor built into the PSU.
However, lets say you have a PSU that doesn't have a pull up resistor built in, you need to put STBY voltage through a 1k resistor to PSon and BLon. If you just put power to PSon alone, it wont fire the backlights.

Tried also to solder a 1k resistor between pin 16 and 4 without success
Thanks

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

You ask me to measure the voltages on IC ICD801, that has 16 pins, and these are the voltages:

1 - VCC - 0V
2 - ISET - 0.8V
3 - GATE - 0V
4 - GND - 0V
5 - CS - 0V
6 - AUTO - 0V
7 - RT - 0V
8 - SYNC - 0V
9 - CLIM - 0V
10 - REF - 0V
11 - PWMO - 0V
12 - OVP - 0V
13 - PWMI - 5V
14 - COMP - 0V
15 - FBP - 1.02V
16 - FBN - 0V

If VCC = 0V then the led driver circuit will not be working. What voltages do you have on pins 1,2 & 3 of QD801 as shown in the diagram.

Is one (or more) of those capacitors leaking since there appears to be some liquid or varnish around the legs?

[thoma]

Re: Samsung 32" power supply BN44-0351B no backlight

http://www.teleservice-depannage.com...-UE32C5100.htm

read let it translate by google!!!!

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

Thanks Thoma,
The link indicated that the fault on that set was DS806/ZDS806 and when replaced brought Multi_VCC back up to 15V.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

If VCC = 0V then the led driver circuit will not be working. What voltages do you have on pins 1,2 & 3 of QD801 as shown in the diagram.

Is one (or more) of those capacitors leaking since there appears to be some liquid or varnish around the legs?

liquid is flux...previous owner tried to replace caps.
Voltages on QD801 are:
1) 13.16V
2) 0.3V
3) 13.32V

http://www.teleservice-depannage.com...-UE32C5100.htm

read let it translate by google!!!!

ok thanks...i will try that solution

Thanks Thoma,
The link indicated that the fault on that set was DS806/ZDS806 and when replaced brought Multi_VCC back up to 15V.

tried to measure voltages...they oscillate:
ZD806:
1) -0.7V
2) -0.6V to -1.6V
3) -0.6V to -1.5V

DS806:
all pins oscillates between -0.6V and -1.4V
So i will have to replace both diodes as indicated in the solution posted by Thoma?

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

Voltages on QD801 are:
1) 13.16V
2) 0.3V
3) 13.32V

For the transistor QD801 pin 2 should be 0.7 volts less than the voltage on Pin 1. So if pin 1 is 13.16V then pin 2 should be (13.16 - 0.7V) = 12.46V

Using you meter set to ohms and with the set powered off, can you measure the resistance between pins 1 and pin 3 and also between pin 2 and DS806.

[seve91]

Re: Samsung 32" power supply BN44-0351B no backlight

sorry i made a mistake on pin number...i suppose that on sot23 the order number of the pins was from left to the right...now i downloaded the datasheet, so i can say:

1) 13.32V
2) 13.16V
3) 0.3V

These measures are taken with only the power supply connected...usually the 13.16V goes down to 12.54V when TV is on.

Resistance measures:
1-3 QD801 = 186kohm
2 QD801 and DS806 = O.L.

[budm]

Re: Samsung 32" power supply BN44-0351B no backlight

BTW, the schematic has the pin NUMBERS assignment wrong for QD801 but the electrical connections are correct as far as E, B, and C are concerned. Some other Transistors can also be wrong too.
KRA104S has the following pin assignment:

Pin 1 is Emitter (the schematic has pin 1 as Base)
Pin 2 is Base (the schematic has pin 2 as Collector)
Pin 3 is Collector (the schematic has pin 3 as Emitter)

It is PNP so if the Emitter has 12V input then the base should have 0.6V less than Emitter for the transistor to conduct, so QD802 has to be turned on for QD801 to be on which is driven by the output of IC802, that IC802 is part of the UVP (Under Voltage Protection), it monitor the D100VDR Voltage (generated by transformer TM802S) which is the feeding Voltage for the LED Boost converter power supply which booste the 100V to much higher Voltage to drive LED's. There are many protection circuits in that board so there are lots of Voltage sensing resistor networks.
You have to watch out on some of these schematics, I found many errors before.
Always check the spec sheet and compare it to the pin number as shown in the schematic.
These power supplies boards are also know for bad solder joints on the board feed through hole, look real close at the transformer legs and legs of the devices attached to the heat sink. I usually re-solder them all for future protection.

[dick_barton]

Re: Samsung 32" power supply BN44-0351B no backlight

sorry i made a mistake on pin number...i suppose that on sot23 the order number of the pins was from left to the right...now i downloaded the datasheet, so i can say:

1) 13.32V
2) 13.16V
3) 0.3V

So are the pin numbers above now referring to the numbers given on the transistor on the power supply schematic or the numbers given in the data sheet for the transistor?


What dc voltage do you have between pins 2 & 3 of ICM801 (MULTI_Vcc) when the set is out of standby. Be careful since this is on the mains side of the power supply.