need help -samsung 32LE5500 power supply not working

[microicri]

Hi to all,
power supply received without few elements,FET, transistor and SMD resistor ( someone try to repair it before).
looking for documentation or possible someone can give me a values of mising elements.

I imediately change viper 27 just to start with something. all capacitors are changed by me too. all diodes tested by meter. all fuses tested too, all ok

at the begining problem was stop working because of night lighting and tv stby stop work. the guy open it before me was just a 15 years old school boy, and he lost elements he remove, but also during soldering something he remove SMD resistor on pin 4 of Viper 27. that pin is FB. loking for value?

thanks for any help. will send picture of board if it can help. ( on request)

[budm]

Re: need help -samsung 32LE5500 power supply not working

We need pictures so we can see what we are dealing with? Any traces on the board get damaged by previous attempted repair?

[microicri]

Re: need help -samsung 32LE5500 power supply not working

Hi there,
here are 3 different pictures of missing elements positions on board.
Thanks for any help.

[R_J]

Re: need help -samsung 32LE5500 power supply not working

The missing resistor from picture #1 is likely a 10Ω (100) resistor, as it goes between the optocoupler and pin #4 of the ic
D201 and D203 are the same, likely MBRF2050CTL
I would think the transistor is just a KTN2222a NPN transistor, it is used to switch the main vcc for main/pfc ic's

[microicri]

Re: need help -samsung 32LE5500 power supply not working

Thanks, will reply to you tomorrow.

[R_J]

Re: need help -samsung 32LE5500 power supply not working

Here is a picture of the resistor and diodes

[microicri]

Re: need help -samsung 32LE5500 power supply not working

Thanks for help,

I search little bit deeper and found one of ZD short(10 OHM). It is ZD503, not sure in value? near IC503

I test circuit with scope, and STBY voltage fluctuate from 3.0 to 3.3VDC and there is no any voltage on ZD503, so VIPER27 go from start to stop and again to start in cycle, but without feed back signal can not continue to work. Also I notice that voltage on pin2 of viper 27 going up and down, so I'm not sure what value of ZD507 should be? According to viper27 data sheet looks like that chip start to work at minimum of 14VDC, so I assume that ZD507 should be at least 14V. Am I right?

I put new NPN transistor for Q511, and try with 10 OHM instead of missing one on position R510 but without FB no operational. Will change optocuplers tomorrow and test again.
If someone have values for ZD's will be nice if I can have it, if not will try to put 15V for pin 2 and 5V for IC503.

Thanks for all help,
Damir

[microicri]

Re: need help -samsung 32LE5500 power supply not working

Here is a picture of the resistor and diodes

Thanks R_J, picture of bottom side is little bit dimly, so I can not see properly, but I will appreciate if you can check for ZD503,ZD507,ZD501 types.

[microicri]

Re: need help -samsung 32LE5500 power supply not working

I see that I miss value some of diodes on drawing, and ZD 503 is wrongly positioned on drawing. Will change it tomorrow and send again, maybe it will help to someone else with same power supply as there is no schematic available online, or I can not find!

[R_J]

Re: need help -samsung 32LE5500 power supply not working

If ZD503 cathode is connected to Q511 base, it is there to set the voltage of Q511 which acts like a regulator, The input is the collector and the output is the emitter, the zener is usually aroud 12~15 volts. This circuit is not needed for standby operation. It supplies the VCC for ic101 (main voltage controller) and ic601 (pfc controller)

[microicri]

Re: need help -samsung 32LE5500 power supply not working

ZD507 on board is 6.8V, and it is changed before I got board. is that proper value? Viper27 start but not continue to work after first wakeing up.

[microicri]

Re: need help -samsung 32LE5500 power supply not working

transformer drive on pin 7,8, after I put 22V zener on pin 2

[microicri]

Re: need help -samsung 32LE5500 power supply not working

Hi to all, I'm sorry but was unable to join group in mean time, so here I am again.
I still have problem to fix this board. I change PC817 in feed back line from secondary coil but still there is 3.0 - 3.3 VDC fluctuate, VDD on viper 27 going from 10-18VDC with pause of about 2 second. transformer driving signal looks ok.
Any suggestions?
Thanks