Sceptre X460BV-F120 2 seconds to power off.

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

Measure the voltage across the suspect capacitor. We expect from 11.5V~25V. It would be a good idea to solder, or wrap around leads on the components, and measure using the flying leads.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

Measured across the cap pointed to in post #38, I get a steady 8.1V until the "click", as I've been calling it, and the voltage briefly jumps to ~9.6V. With the + probe on the + leg of the that cap, and the - probe on the - leg of the big cap, the voltage holds steady at 8.1V but sometimes jumps to ~9.5V and sometimes drops to ~7.5V at the "click".

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

So it's not reaching the right voltage, as that's right near the under-voltage cut-off for that IC.

It is possible the controller IC is faulty (it has become leaky on the Vcc pin.)

Can you measure the resistance that appears across that capacitor?

If it's not that it could be something to do with the network which charges that cap once it is running. There should be two diodes and a small ceramic capacitor for this circuit.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

Should I measure the resistance with the cap in circuit or out?

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

In circuit, we want to measure the Vcc resistance.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

With the DMM on 2000k and the + on the + leg and the - on the - leg, the resistance slowly rises until overload. With the probes swapped the resistance rises to ~1650k and stops.

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

So it's not leaky.

I see the chip is under $5 on eBay. I'd suggest you swap it, if it's not that, we need to look elsewhere -- I'm not sure how to rule it out, other than swapping it. But first, check those other components I mentioned.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

I think I'm just going to replace the whole PSU. There's one online for $45 shipped. Ideally, I'd like to fix this one but I'm beginning to think I could chase it forever and I'll never figure the problem out. I'm not quite ready to throw in the towel but until I know for sure what is causing this issue, I don't want to spend a dime on this psu.

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

Hmm, for a 46", a $45 investment isn't too bad. This is a 120Hz display, too, though I've never liked that feature.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

New PSU came in today and acts exactly like the old PSU. With inverters connected, backlight strobes like a dance party when the PSU is forced on. With the inverters disconnected, the voltage across the big cap is all over the place. I'm not sure where to go from here.

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

Well that makes no sense at all. The problem is almost certainly with the PSU. Was the part guaranteed functional?

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

Yes. My suspicions are starting to point elsewhere, I just don't know where.

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

The only way you're going to see a dip in PFC voltage is a problem with the power supply or perhaps a signal from the main board to PSU is not correct.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

I have the set plugged into a surge protector. With the probes of my DMM on the leads of the primary cap, when I turn the surge protector on, the voltage jumps to 394V immediately and slowly drops to 169V. The whine from the transformer gets higher at the same rate as the voltage drops on the primary cap. When the set is powered on, the voltage on the cap jumps to 394V and stays there until the set is powered off.

This is from post #4, the new PSU acts the same way. It seems like the PFC circuit is working correctly with everything connected.

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

You should check the ripple on the scope outputs and see if it is the same as before.

Also, just checking... you definitely installed the new PSU? Didn't accidentally install the old one? I've done that before!

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

No, it's the new one for sure.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

I'm probably not going to have the time to get back to this one tonight.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

https://www.youtube.com/watch?v=3NKOBHoTocA

The seller of the PSU just responded that this PSU was confirmed to be working when pulled. So, I guess the video is a moot point now. I am going to send this back and get the main from the same guy. I'm not real keen on buying boards on a whim so if it does turn out to be the main that is bad, at the least the seller gets something outta me.

[tom66]

Re: Sceptre X460BV-F120 2 seconds to power off.

I do not trust sellers who say that, they rarely ever test the boards they pull.

Who knows perhaps someone's TV was doing this and in frustration they hit it and broke the screen. Seller picks it up strips it for parts & lists them.

You have ripple on PSU outputs. Is this present with load such as car brake light bulb and no main board/inverter etc.? There is only one way the ripple can happen. The PSU causes it or excessive load causes it.

[johnboy1313]

Re: Sceptre X460BV-F120 2 seconds to power off.

With 12V disconnected from the main but 16V still connected, this happens.

https://www.youtube.com/watch?v=gEnabqLCWys