Samsung PS50C450B1W ,PSU clicking no power

[sigmeyer]

I got this tv for close to nothing , i thought i would have a quick work of it and i was so wrong. The issue is the psu is clicking and i get no power , i have 5 volt stby , the light on tv is coming on then off continuously.
I have taken the board off powered it on alone , and still the same issue. I initially bridged the ps-on pin on the 804-2 connector with 700ohm resistor and nothing happened. Then when i bridge with a screwdriver i hear a double click (2 relays) and then quickly the relays go open and stops untill i release
and bridge it again. I have checked every single transistor on the primary side and the secondary side aswell , checked most of the capacitors with esr meter , and i couldnt find any faults.
When the ps-on is not pulled down i have 2.8volts on it. And other then the 5volt, thats all she wrote.
I probed other points to see if the voltages come up briefly when i close the relays but no. I think there is no oscilation happening of any sort on primary side. The Main filter capacitors have basically 0 volts on them , when the relays click on there is about 300volts. And now i am stuck , i really dont know where to go from this point on , im suspecting some IC is the issue since i cant find any faulty components on board. Mainly im looking at L6598 PWM controller since i cannot hear any oscilation happening for that brief period of time, and the other circuitry is detecting it somehow and just turning it off.
IF anyone has any more experience on this boards maybe you can point me in the right direction.I have some schematics here , but i will post pictures of the board tomorrow since its quite late right now. The schematic is not completely identical but its there 98% same as mine .

[sigmeyer]

Re: Samsung PS50C450B1W ,PSU clicking no power

So heres the pictures and update on what i've tried so far.

back side


So i have removed the resistors and just bridged the ps_on to ground , i can hear a very light click of relay , obviously it does not close, and i found something interesting , one of the transistors is not conducting the 20 volts vcc.
Its the PNP transistor , on the base it has 20volts , on colector (the one going to the im assuming 15volt reg) has 4 volts on it , and 20 volts on emitter . Now it being pnp transistor thats obviously not a faulty transistor , because the base its high ,therefor will not conduct ( i think), so im thinking its something to do with the Quad op AMP thats responsible for not pulling it down , or the other input is not right . Any thoughts would be helpful , heres the picture of what i mean. The transistor is qb803 on the 3rd page of the schematic . you can see how its connected. Im not gonna do anything before i take a look at the datasheet of the op amp see how it works , and maybe It is faulty. the LM324 , i do believe i have a similar quad op amp i can replace it with and see what it does , also its pretty cheap

[sigmeyer]

Re: Samsung PS50C450B1W ,PSU clicking no power

Btw vcc voltage i mentioned is only being created after the regulator, i am not sure if that 20 volts i have read is right , or if its supposed to be higher , if its supposed to be higher then i have found my problem , the ICB802 (the pfc pwm chip) is the only responsible culprit in this case. Please if anyone has this board to tell me if this is right. You can see the board number is PSPF501A01A not sure if i had mentioned before.

[Electrotech68]

Re: Samsung PS50C450B1W ,PSU clicking no power

Worth checking optocoupler ic in feedback circuit and associated components connected to it .. pwm circuits shut down fast if feedback is wrong

[sigmeyer]

Re: Samsung PS50C450B1W ,PSU clicking no power

You are right , i guess it could be on the secondary side aswell with the feedback circuit, also i just noticed on the vcc output out of the VIPER22a (ICB802) there is a 30volt zener diode , so im assuming it should be 30 volts instead of 20 volts i am getting. i have checked the opto couplers with multimeter they seem to test fine. Maybe if i hook up a osciloscope to see what frequency i am getting out of it in regards to what the chip should be getting.

[Electrotech68]

Re: Samsung PS50C450B1W ,PSU clicking no power

Correct .. ZDB804 should clamp 30v across the supply .. worth changing it may be leaky also CB813 I've had this capacitor cause issues in similar psu circuit .. even if capacitance and ESR readings are correct worth changing ..RB830 gone high ?.of course ICB 802 may be at fault dragging this supply down.. one other thing to check is rectifier diodes on the secondary side of transformer not shorted or leakiy .. also check resistance from cathodes to ground are not low shutting psu down .. hope this helps

[Diah]

Re: Samsung PS50C450B1W ,PSU clicking no power

from the photo i do remember this PCB .. don't trust the caps shape and the black mark if they explode or not.. just replace them all at secondary.

[R_J]

Re: Samsung PS50C450B1W ,PSU clicking no power

Replace CB813 and CB815, The vcc for icb802 does not need to be 30v, the zener is for protection not regulation, the ic operates at 15 volts so 20v is fine.

I would check to be sure the Y-sus or the Z-sus boards are not shorted, check the resistance on the VS to ground.

I believe on this board, PS_ON needs to be grounded to turn ON the power supply

[R_J]

Re: Samsung PS50C450B1W ,PSU clicking no power

If testing just the power supply board on the bench you also need about a 1k resistor between VS-ON and stby5v to turn on the VS voltage

[sigmeyer]

Re: Samsung PS50C450B1W ,PSU clicking no power

The capacitors are fine , i have checked them a couple times . The black marks on the capacitors was me marking them as good.Last night i left it plugged in i forgot to flip the switch on my mains supply. Now i checked and there was no ps_on voltage. Before it was 2.8v or something now it was zero.
I suspected the Quad op amp KA324 and i replaced it with what i had lying around the LM224 just to test. Now i get 4volts on ps_on and same clicking as before just a bit less loud. It was probably me who damaged the op amp , even tho i am not sure how , or maybe because it was left on to work overnight.
I do believe both op amps on primary and secondary side are not working properly. I will order some parts tomorrow and see if i get anywhere with this.

I may have damaged the op amp on the primary side when i was trying to check if the relays are working with the Power supply because i did short 2 flyback diodes that i replaced.

[nomoresonys]

Re: Samsung PS50C450B1W ,PSU clicking no power

Look your solder joints over closely, make sure none are bad.

[sigmeyer]

Re: Samsung PS50C450B1W ,PSU clicking no power

I did look over solder joints , they are fine , the ones i can see well anyway. I replaced both op amps and it does the same thing. Today i have however found out that the KIA7815 regulator is bad... its outputting 8v instead of 15 . Maybe this was my problem all along or maybe i damaged it somehow , but like i said it was working fine one night , then after i left it plugged in over night i get this. i will order a new one and see where that gets me. Also it did have a small heatsink on it so maybe it was inadequate ... also this regulator would be turned on all the time for the tv to work

[dskall]

Re: Samsung PS50C450B1W ,PSU clicking no power

Need to check for shorts after you remove regulator.

[sigmeyer]

Re: Samsung PS50C450B1W ,PSU clicking no power

Ye im right on it , i hooked it up so that output of the regulator is floating . Its outputing 8volts so its definitely bad. I will replace it , along with some transistors surrounding the "start up" circuit on the primary side. I can also see some voltage is supposed to be getting to the op amp on the primary side , from all 3 other ICs. So im assuming thats how it checks if everything is okay and it can continue working.
Anyways i ordered some regulators they are arriving tomorrow so i will see if that solves the issue. I do seem to remember the regulator outputting like 12 volts instead of 15 before i even started to mess with things.

[sigmeyer]

Re: Samsung PS50C450B1W ,PSU clicking no power

After replacing the 7815 reg , the issue was solved , and now the psu turns on and stays on. I suspect that was the problem all along. But ofcourse now that i have replaced both quad opamps maybe they were the issue too but i doubt it. Anyways that was my repair of this psu... not a very hard one but became really hard when you cant measure things in about 1 second at a time. If anyone has the same problem i suggest first checking the regulator IC on primary side and see if you get 15 volts.

[sigmeyer]

Re: Samsung PS50C450B1W ,PSU clicking no power

You can check it by shorting the base and collector of that driving transistor