Samsung 32" power supply BN44-0351B no backlight

[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.

[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

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

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

nope, no voltage

[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

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

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

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

[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

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

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

[dick_barton]

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

In your first post #1, you said you had sound and picture but no backlight so that would indicate that either the led voltage is missing, led driver is faulty or there is an led fault.

ICP801 drives the circuits that give you the secondary voltages A, D12V, Vamp, D5.3 and STBY5.2V and since you said everything but the backlights are working then its not likely that ICP801 is faulty.

You also said earlier that pin 2 (as shown on the schematic) of QD801 was at 0.3V and this supplies the voltage to pin 1 of ICD801. If this is the case then without a supply voltage to that IC, there can be no led boost voltage.

ICM801 pin 3 (VCC) = ??
ICP801 pin 8 (VCC) = ??

[seve91]

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

Ok....

ICP801 pin 8 (VCC) = 1.60V
ICP801 pin 1 (FB) = 1.84V
ICM801 pin 3 (VCC) = 1.62V

[dick_barton]

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

Did you put your black meter lead on power ground to take the readings and not on the chassis?

[seve91]

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

black probe put in the GND pin of each IC measured

[dick_barton]

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

I think the problem is around QS801 and the diodes as indicated by Thoma in an earlier post.
There is 13V at pin 3 of QS801 and when Power On/Off is taken high and the opto-isolator PCS802S/B acting as a switch then shorts the 13V to RS809/RS810 taking the base to 13V. The emitter voltage should then be at the base voltage minus 0.7V.

As a quick test, but at your own risk, I would quickly short QS801 emitter and collector to enable Multi_Vcc and see if the backlights come on.

[seve91]

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

short done, and TV is working!!! THANKS A LOT!! so maybe is the opto isolator that doesn't switch on the QS801?

[budm]

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

So what is the PFC Voltage now?
ICS802 is part of the PFC Over Voltage protection that will not allow QS801 from coming on by bypassing the bias current for QS801 to GND.

[dick_barton]

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

As Budm has requested, what is the PFC voltage when the set is forced on by shorting emitter/collector?

You need to check QS801. Youtube have plenty of video's that show you how to test it with your meter. The opto-isolator is fine and does not need to be replaced. It shorts the collector voltage to the base of QS801 when the Power ON/OFF input is taken high as it should.

I would also replace the zener diode ZDS806 and diode DS806 connected to the base of QS801 as suggested by Thoma then your tv will be repaired properly.