Samsung PN50A550S1F SMPS Cycling On/Off

[Ltank]

Tv power supply cyles on/off. I removed the plugs from the Y, Z and X boards and no change. If you remove the plug from the control board the PS does not turn on. I checked the plug to/from PS and mainboard. When the PS_On is active low the PS turns and VA and VS and all voltages come up then it cycles High to about 3.2vdc and it resets the PS. Unplugging the plug at PS and connecting a 100 ohm resistor to chasis ground and the PS_On pin #4 the PS stays powered up. I assume that High pulse is from the main board telling it to shut down???
Is it a SMPS problem or a X,Y,Z problem reporting a problem to control board telling the main board to shut down or the main board?
Any help is greatly appeciated.
Thanks
Ltank

[Ltank]

Re: Samsung PN50A550S1F SMPS Cycling On/Off

Does the Ps_On command or signal come from the main board to SMPS to tell it to turn on or the signal come from the SMPS to the main board? On this set a low makes ps voltages stay on and a high resets ps.
Thanks
Ltank

[capkid]

Re: Samsung PN50A550S1F SMPS Cycling On/Off

You might be able to run this test: https://www.badcaps.net/forum/showthread.php?t=26790

Edit: PS_ON is sent from the main board to the PSU.

[Ltank]

Re: Samsung PN50A550S1F SMPS Cycling On/Off

Hi
I have a Samsung Plasma TV that the SMPS turns on and produces all the correct voltage when a low is applied to the pin and a 3.3 v resets the PS. All the post I find here tell me it should be 3.3 v to 5 v. My set appears to be backwards. I guess I can remove the wire from the plug to main board and supply a 100 ohm path to ground to turn on supply and monitor the voltage from the main board at the same time. Maybe the SMPS has a bad If or transistor the path that is messing with my logic. I am doing this from my cell phone at the moment and don't have access to my partial schematics of the service manual.
Thanks
Ltank

[capkid]

Re: Samsung PN50A550S1F SMPS Cycling On/Off

You may not need this: http://www.youtube.com/watch?v=dVaC2KVVLvs

[Ltank]

Re: Samsung PN50A550S1F SMPS Cycling On/Off

I removed the SMPS and inspected board on foil side then reconnected it. I removed the # 1 PS_On wire from CN801 and measured the voltage. It cycled .24 to 3.3 vdc. from the main board. I did find out that a low turns it on for this set. Then I jumperd #3 and #4 on the control board then jumpered #1 pin low to turn on the set and the set cycled through a series of test patterns. Now I know the PS, Control, Y, X and Z boards are fine. I ordered a a main board. Is Samsung the only sets that allow this?

[capkid]

Re: Samsung PN50A550S1F SMPS Cycling On/Off

I'm unsure of your question. If you're talking about test patterns, some LGs also being allow you to run tests: https://www.badcaps.net/forum/showpo...01&postcount=8

Panasonic test: https://www.badcaps.net/forum/showthread.php?t=26790

[Ltank]

Re: Samsung PN50A550S1F SMPS Cycling On/Off

Go the main board in today and it works Great! No cycling on/off. Has a good picture. Thanks Guys!!