PSLF201501B BN96-03057A Blown Capacitor

[LugNut]

My TV uses the board BN96-03057A, model PSLF201501B.

The original issue was the standby light would go on then immediately turn off - TV would not turn on. Pulled the board to found 3 caps bulging so I replaced them.

After replacing the caps and confirming the fuse was good, I plugged the board into the wall. At that point the board was not generating power. Checked the fuse and it was blown.

I replaced the fuse a second time, plugged it in, and poof - cap NT811S made quite a pop! In hindsight, I had read somewhere that you can use a 40 watt bulb in place of the fuse. If it lights you have a short.

Here is my thought process for trouble shooting:

1. Pull the bridge rectifier to isolate the AC from DC
2. Test the bridge rectifier
3. Replace the popped cap. Not sure I can read a number off it
4. Apply AC power and check for 120v potential where the rectifier was
5. Check for a short on the DC side by injecting low power into the rail
6. If no sort found, install the rectifier and the light and give it a go.

Is my thought process close? I do not have the schematic, but I can kind of make out the paths.

Thank you.

[petehall347]

Re: BN96-03057A Blown Capacitor

one of the caps you changed was installed backwards or wasn't suitable .

[LugNut]

Re: BN96-03057A Blown Capacitor

if you changed NT811S it was installed backwards or wasn't suitable .

Thank you, but I did not change NT811S. Pretty sure it is a nonpolarized cap.

[petehall347]

Re: BN96-03057A Blown Capacitor

i looked at pic after then edited my post .

[R_J]

Re: BN96-03057A Blown Capacitor

NT8115 is NOT a capacitor, it is a NTC thermistor 5Ω cold. Check that QP801s is not shorted, if it is, RP819 is also likely open. Check if FS802s fuse is ok, if it is ok then that eliminates most of the power supply circuit.

[R_J]

Re: BN96-03057A Blown Capacitor

The thermistor is likely a 5D-13

[Robinsosa]

Re: BN96-03057A Blown Capacitor

I hope this is the schematic diagram for the power supply.

[LugNut]

Re: BN96-03057A Blown Capacitor

NT8115 is NOT a capacitor, it is a NTC thermistor 5Ω cold. Check that QP801s is not shorted, if it is, RP819 is also likely open. Check if FS802s fuse is ok, if it is ok then that eliminates most of the power supply circuit.

Thanks RJ. FS802S is ok. I pulled QP801S out of the circuit and tested it with my component tester, which shows it is good. I did the multimeter test and it checked out good. I also pulled out RP819 - it is not open but has 0.3 ohms resistance. Is that good?

I looked at the datasheet for QP801S to learn more about it. I found some test circuits I am going to breadboard up to learn a little more before I stick it back in the board.

One thing I could not find information on is that the drain(2) is shorted to the back plane of the TO-247 package. Is that correct? Unless I missed it, it does not show in the datasheet. It was late when I checking it.

Thank you for helping me get this fixed.

[R_J]

Re: PSLF201501B BN96-03057A Blown Capacitor

Yes the mosfet drain is connected to the tab, if the mosfet is not shorted drain to source it is likely ok. it sounds like the thermistor could be all that is wrong.

[LugNut]

Re: PSLF201501B BN96-03057A Blown Capacitor

You were spot on with the 5D-13. Ordered a couple from mouser. Should be here in a couple of days.

[LugNut]

Re: PSLF201501B BN96-03057A Blown Capacitor

UPDATE: Replaced the thermistor and fuse. There was 6V on the standby. Installed the board in the TV. When I turned it on, the MOSFET shorted and caused a bit of smoke and blew the fuse. I have replaced the MOSFET and fuse. Confirmed there is 6V on the standby. Installed the board back in the TV.

Now the standby light comes on but immediately goes off. Pushing the power button does nothing.

On the bench, the 6V is constant. I am concerned that it may be something in the main board now.

If I jump the ST_BY6.0V pin to the PWR-ON/OFF will that start the board and provide the 5.4VLINE and 24VLINE voltage to confirm they are working?