NS-50L440Na14 LCD Power supply issue

[Nick's Tvs]

Power supply AY158P-4HF03

I checked AC coming in from power cable, and got proper 120V, but I couldn't get any voltage through out the board. After further inspection, I found out that the inductor at location LF3 was burnt. I have never had to replace an inductor before, and was not sure what would be an acceptable replacement. I am assuming any inductor from a salvaged board wouldn't work correct?
I also don't see any rating what so ever on this inductor.

[Nick's Tvs]

Re: NS-50L440Na14 LCD Power supply issue

Additional picture of the inductor taken out.

[R_J]

Re: NS-50L440Na14 LCD Power supply issue

Thats just the ac input line choke, I doubt its bad. did you check the fuse?

[budm]

Re: NS-50L440Na14 LCD Power supply issue

You have 3 Line Filters connected in series, that first one can be bypassed and you probably will not notice any difference in the performance of the TV.
See what this brand did to that filter: It is bypassed.
https://www.badcaps.net/forum/attach...4&d=1454004176
Do you have any scrapped old TV power supply boards? they are just a common mode chokes.

[Nick's Tvs]

Re: NS-50L440Na14 LCD Power supply issue

Thanks budm
I did the bypass and the tv works fine. I ended up doing some more searching and finding a replacement for it and got a compatible part from a scepter tv.
Ran it for 3-4 hours before having my customer pick up.
Very odd, never seen one of those go out before.

[budm]

Re: NS-50L440Na14 LCD Power supply issue

Thanks for the follow-up.

[paul726]

Re: NS-50L440Na14 LCD Power supply issue

I'm trying to troubleshoot this same board from a TV I got at work that, if I can repair it, will become a wall-mounted fourth monitor for my computer.
Is there a list of test points available somewhere so I can probe through it to see whether it's bad or not?
The TV doesn't power on when button is pressed, and I verified the button is functioning.
The power supply has no DC outputs when plugged in, but I don't know if it receives a control signal to turn them on (though it appears not). Any information would be much appreciated.

[budm]

Re: NS-50L440Na14 LCD Power supply issue

I'm trying to troubleshoot this same board from a TV I got at work that, if I can repair it, will become a wall-mounted fourth monitor for my computer.
Is there a list of test points available somewhere so I can probe through it to see whether it's bad or not?
The TV doesn't power on when button is pressed, and I verified the button is functioning.
The power supply has no DC outputs when plugged in, but I don't know if it receives a control signal to turn them on (though it appears not). Any information would be much appreciated.

Please upload straight shot and very clear pictures of your board top and bottom side so I can give you the test points to test.

[paul726]

Re: NS-50L440Na14 LCD Power supply issue

I misspoke (mistyped?) earlier. I do have the 5vsb present. I can't locate the equivalent of pson to check other outputs.
I have 120vac through all where I expected it, and 50vac on the jumpers to the right of the heatsink in the hot side.
Thanks for your tutorial, that's moved me along a bit thus far.

[budm]

Re: NS-50L440Na14 LCD Power supply issue

Connector CN2 'SB' pin is the PS-ON pin.

BTW: 'and 50vac on the jumpers to the right of the heatsink in the hot side.'
You were using Black probe of the meter on the chassis GND as the GND ref for your meter?

[paul726]

Re: NS-50L440Na14 LCD Power supply issue

I suspected the SB, as the PSON shown in your linked tutorial shows it with the rest of the dc outputs.
I used the neutral on the AC input - the line side of the cap, as the reference for the AC readings, including the 50vac I found.

[budm]

Re: NS-50L440Na14 LCD Power supply issue

So what do you have on the SB pin? If the SB is present then the DCV between the two legs of the main filter cap should be close to 400VDC.
Any measurement after the bridge you will use the Negative leg of the main filter cap as the GND ref for the measurement.

[paul726]

Re: NS-50L440Na14 LCD Power supply issue

A'ight. The board's out of the TV right now. I get nearly 6vdc on 5vsb (non-regulated?). Anyway, when I jumper 5vsb to the sb pin, I get 386v on the filter cap, but nothing on the 5, 12, or 24v pins when referenced to either the negative cap leg or the gnd pins. Well actually, I get about .7v on the 12v pins.

[budm]

Re: NS-50L440Na14 LCD Power supply issue

A'ight. The board's out of the TV right now. I get nearly 6vdc on 5vsb (non-regulated?). Anyway, when I jumper 5vsb to the sb pin, I get 386v on the filter cap, but nothing on the 5, 12, or 24v pins when referenced to either the negative cap leg or the gnd pins. Well actually, I get about .7v on the 12v pins.

OK, the PFC Voltage booster is working.
When checking the DCV (I.E. 5V, 12V, 24V) on the COLD side, will use GND pin on the connectors or if the board is mounted the metal chassis then you can use the chassis as the GND ref.
You use Negative leg of the main filter cap when you are making the Voltage measurement in the Primary DC side of the circuit.
You should check the batteries on your meter to make sure it is not low.

[budm]

Re: NS-50L440Na14 LCD Power supply issue

BTW, I need to see the whole backside of your TV so I can see how all the connectors are connected together between boards.

[paul726]

Re: NS-50L440Na14 LCD Power supply issue

Meter battery was just changed out. Won't be able to put board back in TV before tomorrow. VDC output measurements were being taken referenced to gnd pins. Does the lack of dc outputs now (with 5vsb jumpered to sb) indicate the board is bad?

[budm]

Re: NS-50L440Na14 LCD Power supply issue

Meter battery was just changed out. Won't be able to put board back in TV before tomorrow. VDC output measurements were being taken referenced to gnd pins. Does the lack of dc outputs now (with 5vsb jumpered to sb) indicate the board is bad?

It indicated that the switched POWER MOSFETS (Q9, Q10, Q14) are not being turned on to supply the switched 5V, switched 12V, switched 24V, for all 3 the be dead due to all bad MOSFETs are not likely.
That is why I want to see how the boards are being controlled by looking at the pictures of how all the boards are connected together.

[paul726]

Re: NS-50L440Na14 LCD Power supply issue

Here're the boards connected up. TV's standiing on its head, if that matters. I'm reading about 5.9 on 5vsb and 5.1 on sb, about a diode's difference. Pushing power on doesn't not light anything and no readings changed after doing so. I didn't attempt reading holding the button in, but verified prior an input change on the yellow/black/blue wires running to the control board from the button panel while pressing the power-on button.
By the way, lest I forget to say it, I greatly appreciate your help with this.
Thanks!

[pjpa]

Re: NS-50L440Na14 LCD Power supply issue

I also have a similar problem. I had no 120V past LF3 and found one side of it open. I also found that the component right next to it in shrink tubing was open. it is marked 105681K but I don't know what it is or its purpose in the circuit, Can anyone help? Is it possible to get a schematic?

[budm]

Re: NS-50L440Na14 LCD Power supply issue

I also have a similar problem. I had no 120V past LF3 and found one side of it open. I also found that the component right next to it in shrink tubing was open. it is marked 105681K but I don't know what it is or its purpose in the circuit, Can anyone help? Is it possible to get a schematic?

Show us the pictures of YOUR board and the component in question. The part in question should have designator printed on the board for that part.
So do have DCV between the two legs of the main filter cap?
When you say 'similar problem' what is the exact problem?