Samsung 32" power supply BN44-0351B no backlight

[seve91]

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

maybe ICP801 is dead...i believe that the IC controls the boost of the PFC

[seve91]

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

the OUT of the BD801S is 323V, the DP801 and DP803 diodes are ok.
So how could be PFC_OUT 400V? Where is the spot of the circuit where PFC is boosted up to 400V?

[seve91]

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

yes, same voltages in PFC when TV is on

[seve91]

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

ok so that part is not switched on...i will try to put the board back to the TV and power it on, then i will measure again the voltages

[budm]

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

The PFC boosted Voltage should be close to 380~400VDC range when the TV is turned on, 323V is normal Voltage in standby (230V x 1.414 = 325V).
So if that is what you have when TV is turned on then you need to start checking the PFC section. Check to see if the PFC Diodes are OK or not.

[seve91]

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

the high voltage line seems to stop on the hot side of the TM802 (PFC_OUT is 323V)

[budm]

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

nope, no voltage

Well that is the section of the circuit you need to check and find out why it is not putting out any Voltage to feed the LED Voltage booster power supply section.

[seve91]

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

nope, no voltage

[budm]

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

As explained earlier, that protection circuit monitor the D100VDR Voltage, if it is not present or too low then that transistor will not be turned on as you can see in the schematic.
So do you have Voltage at D100VDR as shown in the diagram?

[seve91]

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

Right now that Transistor QD801 is not turned on, that Base pin 2 should be < 1V or when QD802 is turned on as explain in my earlier thread.

yes i know...so? what's the next step?

[budm]

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

pins are ordered as reported in the datasheet:

1) 13.34V
2) 13.17V
3) 0.4V

dc voltage between pin 2-3 of ICM801 is 1.58V (only PSU connected, with 1kohm resistor between pins 16-18 of CNM801.

Thanks budm for your tip and suggestions...checked the solder around the transformers, and other main devices...they are good.

Right now that Transistor QD801 is not turned on, that Base pin 2 should be < 1V or when QD802 is turned on as explain in my earlier thread.

[seve91]

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

pins are ordered as reported in the datasheet:

1) 13.34V
2) 13.17V
3) 0.4V

dc voltage between pin 2-3 of ICM801 is 1.58V (only PSU connected, with 1kohm resistor between pins 16-18 of CNM801.

Thanks budm for your tip and suggestions...checked the solder around the transformers, and other main devices...they are good.

[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.

[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.

[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.

[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

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

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

[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

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?