Westinghouse SK-26H735S Power Supply Problem

[kevinm34232]

The TV is dead, main fuse is good. Have 120VAC voltage at connector CN1 but no voltage at center pins of bridge rectifier. Center pins show short. Removed bridge rectifier and tests good. Center pads show short. Not much experience in what can go wrong before this point but this seems like a very simple design.

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

In the pic you can see where the bridge rectifier center pins are, is it supposed to be low ohms between these pins?? Without the bridge rectifier installed I still do not get the 120VAC there I just cannot figure out why and there's not much there so I feel kinda dumb!

Also, with the bridge rectifier removed can anything else on the DC side cause this?

[budm]

Re: Westinghouse SK-26H735S Power Supply Problem

If the bridge at the top left of the board is shorted (or shorted load), then I would expect the main fuse to blow.
I look at the traces, the two pins are connected both ~ pins together. I will have to trace out the connection to see how it is designed.

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

The thing is Bud that it tests fine out of circuit, but in circuit ~ pins show short and removed, the ~ pads show short, is that normal? I edited the post above if you can looks at it and see if something could be blown or shorted..??

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

As I said not too familiar with components over in this area but RV001 (varistor?) is open. Should it be?

[budm]

Re: Westinghouse SK-26H735S Power Supply Problem

I am tracing out the circuits right now, that in-rush current limiter RT001 should have low resistance around 3~5 Ohms. What are the numbers printed on the body? RV001 is the MOV for surge protection, it should show open circuit.

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

RT001 is around 5 ohms, SCK 055.

In post 2 picture 2, there is a blue component with EL109, is that a coil? It tests open with meter and with a ring tester no lights.

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

Nevermind
http://www.alldatasheet.com/datashee...AYA/LE474.html

Im lost..

[budm]

Re: Westinghouse SK-26H735S Power Supply Problem

OK the bridge rectifier is connectED as the voltage doubler circuit, you should see about 160VDC on the each one of the main filter caps. The total out put is 320VDC.

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

First though I have no VAC to the center pins. I don't know why, and don't understand why the bridge rectifier center pin pads have 0 ohms between them.

[budm]

Re: Westinghouse SK-26H735S Power Supply Problem

They are tied together so it can be used for the voltage doubler circuits. Is there any voltages on any pins of the connectors on the right side of the board, the small transformer is more likey to be for the 5V power supply.

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

I get 160vdc on the caps! I don't get it but it's there, sorry. When I didn't see the AC voltage I stopped, never seen this before... Let me check other voltages now..

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

Im thinking maybe a main board problem, voltages are erratic. The only one that is consisent is the 5v Stdby when not plugged into main board.

[kevinm34232]

Re: Westinghouse SK-26H735S Power Supply Problem

Well Im not sure now, if I jump the 5v Stdby with 3.3k resistor to PS_ON with main board connector unplugged, I get no backlight and the 24v comes up and slowly drops off.. Would this indicate a backlight problem?

[budm]

Re: Westinghouse SK-26H735S Power Supply Problem

For the backlights to come on it needs these signals: 24V (PS_ON to turn on the 24V power supply), BL_ON to turn on the inverter circuits, PWM signal (about 200 Hz) for dimming if it uses the PWM signal for dimming control instead of the analog Dimming signal.
If the main board is not sending out the PS_ON, BL_ON then you need to start looking at the main board.

[bmolke]

Re: Westinghouse SK-26H735S Power Supply Problem

I have this exact tv which does not turn on. I have found that the 12v output is only reading 5v and the 24v output is only reading 17v. what can cause the low outputs on the power supply. Can it be bad caps(although none are bulging). Not sure why the power supply is reading so low. I am a complete newbie so any help would be appreciated

[budm]

Re: Westinghouse SK-26H735S Power Supply Problem

Are the output voltages steady or they are jumping up and down? If it is steady, then it can be bad regulation feedback circuit. Caps looks OK? Any pictures of the board?

[bmolke]

Re: Westinghouse SK-26H735S Power Supply Problem

voltages are steady, caps look ok. I can upload picture later but don't have camera right now.

[bmolke]

Re: Westinghouse SK-26H735S Power Supply Problem

not sure this is a good enough picture but voltages are steady. what can I check. I am new at this and any help would be appreciated

[budm]

Re: Westinghouse SK-26H735S Power Supply Problem

"I have this exact tv which does not turn on. I have found that the 12v output is only reading 5v and the 24v output is only reading 17v." OK, since you do get some voltage on the 12V and the 24V outputs, that means the mainboard is sort of working because it does send out the PS_ON signal to turn on the 12v and 24V power supply (by the way, the 12v and the 24v are generated from that large transformer). You must have some kind of LED indicator of some sort to tell you the TV is on or off. The 5V stby is 5V, right?