SCEPTRE x425bv-fhd NO video Powers Up

[Neonpeon]

I need some help on this one please.
SYMPTOMS: Black Screen
I WAS able to get the SCEPTRE screen to come up after it had been off for a couple of hours. Have replaced the Main board. Same Symptoms.
Plug it in, I get RED light, Hit the power button light goes blue.
I can not power off without unplugging it.
I have checked voltages on power supply, they all seem fine.
If I unplug the cable from the video board to the inverter, I get backlights.
Also I don't seem to be getting much power to the Tcon, not sure where to look here.

[freakaftr8]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Get a can of freeze spray and hit the power supply caps. Look into the screen with a flashlight to see if there is video

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

I'm out of compressed air. Sent the wife to town.

I was able to get it to come up once after being plugged in for about 5 minutes, it just popped on. It went back out after about another 5 minutes, and I was unable to get it to come back up.

Voltages on the power supply seemed to be close to the same with it
running or not. The high voltage cap is normally at 326v and when running jumped up to 333v.

I have voltages on the tcon when when it is running as well, didn't measure them though.

The 2 pin connection to the inverter board voltages changed.
Not running
0.0v
5.1v

Running
5.1
2.1

As soon as the wife gets back, I'll try freezing the caps.
It's almost like it is in standby mode, not turning on completely.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Almost forgot. There is no video on the screen when shining into it with a light.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Freezing the caps may have helped it to power up once, but I couldn't associate any particular cap as being bad.

Just ordered an ESR meter. Should be here Wednesday. I've been working on enough of these lately, it should save a lot of time. I'll post back after I check the caps.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Checked all the caps on the power supply, and inverter board. (Except the surface mounts).

Loving the ESR70 by the way.

I have 5v and 12v and 24v on the power supply.
I have 3.3 1.2 1.8 5.1 on the main board. Regulators appear to be ok.

Shouldn't the main board be supplying the turn on voltage for the inverter?
Can someone explain how this works?

I'm wondering if I just got a bad main board.
Can anyone recommend what to look at next?
I'm not giving up on this one.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Anyone?

[budm]

Re: SCEPTRE x425bv-fhd NO video Powers Up

There is BL_ON (backlights on) or sometime called INV_ON to turn on the backlights, it comes from the main board. You should look at the inverter board pin out. Post good clear pictures if the inverter board and the area around the connector. Main board also sends out Dimming control signal for backlights dimming. Both of these signals are routed through the power supply board (this is done on most TV).
Read my basic LCD TV troubleshooting guide.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Heres a pic of the Inverter connection.
I am not sure what DET IPWM and EPWM are. I assume BLON is Back Light on.

[budm]

Re: SCEPTRE x425bv-fhd NO video Powers Up

So when the TV is powered up, the BL_ON should be around 2~5vdc range for the ON signal.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Yes, 2.1 is what I get when I did get it to come up.
BLON is 2.1 when running.
EPWM is 5.1 when running.

In the current state:
BLON is 5.1
EPWN is 0.0

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

I might also add that the only connections other than the 24 v and ground are the BLON and EPWM.
Both these connections run to the main board.
If I unplug the connector on the main board I get backlights, but nothing else.

[budm]

Re: SCEPTRE x425bv-fhd NO video Powers Up

EPWN (External Pulse Width Modulation) is 0.0 that is not right, this is the Pulse-width-modulation dimming backlights brightness control, it is an AC signal around 200Hz with variable pulse width. What you can do is to disconnect this wire and see if the backlights will stay on.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Nope, Disconnected pin 14. No backlights. If I also disconnect pin 12, I get backlights.

[budm]

Re: SCEPTRE x425bv-fhd NO video Powers Up

That works in reverse then for the BL_ON, normally HI = on, LO = Off. But the bottom line is that if you do get the light source to stay on then you should see the pictures on the screen OK, no? Right now it points to bad main board.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

No, Here is what I have when I plug in the tv.
I get a RED light, Standby mode.

When I hit the power button the light changes to Blue and stays there.
If I hit the power button again it still stays Blue.
I have to unplug the power cord to reset it.
I do not have any power going to the tcon at all, the backlights don't come up, however all the voltages on the power supply are correct.

However, once in a great while, it will start up and I get video on the screen and power on the tcon board and everything works correctly, I can press the power button, and the tv will power off, but it only lasts a couple of minutes, then it goes back to what I have now.

[Neonpeon]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Ok, Thats what I thought on the main board. I have already replaced the main board, but I could have got a bad one I suppose.

[whatusername]

Re: SCEPTRE x425bv-fhd NO video Powers Up

I am have the exct same issue with my mothers tv.. same model as yours... did getting a new main board fix the problem? any updates?

[whatusername]

Re: SCEPTRE x425bv-fhd NO video Powers Up

The weird thing about it and what is confusing me is if it is the main board why does it turn on still and stay on all day long with no problem?

[johnboy1313]

Re: SCEPTRE x425bv-fhd NO video Powers Up

Just for a test, unplug the T-Con board and power the set on. Will it power off with the button then? I had a Sceptre X460BV with similar symptoms that turned out to have a faulty T-con board.