Testing AC on SMPS

[tech2014]

Hey guys. I don't have much experience with primary side of SMPS circuit. Most faults I get are on the secondary side. When testing AC on the SMPS primary side, do I use the negative leg of the filter cap for ground. I am testing the 120VAC to see where I lose it, since its not getting to the bridge rectifier. I don't have a schematic.

[budm]

Re: Testing AC on SMPS

You need to test the ACV BETWEEN the two ~ pins of the Bridge rectifier with ACV meter to find out if the incoming AC reach the Bridge rectifier ~ pins or not, the Negative legs of the main filter cap is the GND ref of the primary side circuit which is AFTER the bridge rectifier (+/- OUTPUT of the bridge).
Show us the pictures of top and bottom side of the board so we can see the path of the incoming AC.

[tech2014]

Re: Testing AC on SMPS

I got 0V when measuring the two middle pins on the bridge rectifier. I checked the rectifier on diode test and it measured ok. I am also trying to draw a schematic for the AC side just to help.

Here are pics of the top and bottom of the board, the AC side.

[budm]

Re: Testing AC on SMPS

Can we see the straight shot pictures of the whole Top and Bottom side of the board? The AC to the ~ of the bridge may being fed through the relay but I cannot tell until I see the pictures of the whole board.
What is the make and model of this board?
I assume you already test the fuses.

[CapLeaker]

Re: Testing AC on SMPS

did you check that fuse? Everything in front of the bridge rectifier is AC.

We need straight shot, high resolution pictures, front and back of the board.

[tech2014]

Re: Testing AC on SMPS

yup I tested the fuse. The TV model is Samsung PN51D550C1FXZC. I can't take decent pics with my camera so SJ link below.

Board part number is bn44-00444A.---

https://www.shopjimmy.com/samsung-bn...upply-unit.htm

[budm]

Re: Testing AC on SMPS

As you can see from the trace on the bottom side of the board, the AC goes through the power relay contacts to the ~ of the bridge, so if the power relay is not on then you will not get AC at the ~ pins of the bridge.
Pictures provided by shopjimmy.