Sceptre X20WG-Naga inverter problems

[HawkPidgeon]

So I have a Sceptre X20WG-Naga LCD monitor, and it won't turn on. The power light on the front works, but nothing else does. I suspected the inverter and decided to test it. Sure enough, it wasn't outputting on the 12v rail and I noticed two of the smaller caps on the board were leaking yellowish fluid.

I replaced all of the 470uF @ 25v caps on the board with new ones from other monitors (which had various problems like shattered LCDs). After that, the Sceptre power supply still didn't work. Just to make sure, I tested the large capacitor on the board (68uF @ 450v) and it seemed to be working fine. I soldered the big cap back into place and retested the inverter, and about twenty seconds in, I heard a loud pop and saw a bright flash coming from the same cap. I guess I left two solder points touching accidentally or something.

I checked everything to make sure nothing was touching, and now the power supply doesn't output on its 5v rail either. Where before I could hear the large capacitor charging and discharging much like the cap in a disposable camera, now the inverter is completely silent.

I've looked for replacement inverters online, but can't find any. If anyone has a particular parts store that they like, I'd really like to try looking there.

I'm assuming I'm out of luck, but is there anything I can do?

Sorry for my noobishness; this is my first time trying to fix a monitor.

[HawkPidgeon]

Re: Sceptre X20WG-Naga inverter problems

Woot! I got the 5v rail again. I realized that I blew the fuse when the capacitor discharged (apparently it accidentally touched a pair of pliers I had laying nearby), so I've bypassed the fuse and I'm... right where I started. Could it be something other than the capacitors?

[PlainBill]

Re: Sceptre X20WG-Naga inverter problems

Woot! I got the 5v rail again. I realized that I blew the fuse when the capacitor discharged (apparently it accidentally touched a pair of pliers I had laying nearby), so I've bypassed the fuse and I'm... right where I started. Could it be something other than the capacitors?

Probably. The usual design of the SMPS found in monitors has 5V and 12V generated by separate windings on one transformer. It is EXTREMELY unlikely that bad caps would explain the lack of 12V while 5V is present.

"One picture is worth a thousand words." The more information you give us, the more we can give you.

Bypassing a fuse is right up there with lighting a match to find a gas leak and looking into the muzzle of a gun to see if there is a round in the chamber.

Information on inserting pictures.

PlainBill

[HawkPidgeon]

Re: Sceptre X20WG-Naga inverter problems

Probably. The usual design of the SMPS found in monitors has 5V and 12V generated by separate windings on one transformer. It is EXTREMELY unlikely that bad caps would explain the lack of 12V while 5V is present.

So should I check to see if the transformer is somehow not working?

"One picture is worth a thousand words." The more information you give us, the more we can give you.

I'll see if I can get my dad to bring home his work camera tomorrow.

Bypassing a fuse is right up there with lighting a match to find a gas leak and looking into the muzzle of a gun to see if there is a round in the chamber.

Yeah, I know, but I don't have a fuse to replace it. I'm not sure it's quite as dangerous as lighting a match to find a gas leak, though. xD

Thanks for your help.

[HawkPidgeon]

Re: Sceptre X20WG-Naga inverter problems

Alright, so I manually added some electricity to the twelve volt rail and found out that didn't help. I've also discovered that when the monitor is off, the front LED should be red, and when it's on the LED should be blue. Currently, both the red and blue LEDs are lit, which makes me think it might be a controller issue.

I've also noticed that when I plug the monitor into my computer, my computer can detect the monitor and its supported resolutions, and can try to use the monitor. If I shine a bright light over the monitor, I can see that there are bars of grey and black going up and down the LCD. I'm beginning to doubt that this is a power supply issue.

As far as the "broken" 12v rail goes, I see that there's a pin on one of the inverter connectors that says "BL", which I assume means that's the pin that can be used to trigger the backlights to turn on. Maybe the power supply also turns on the 12v rail when the backlights are triggered.

[FreshPancakes]

Re: Sceptre X20WG-Naga inverter problems

Has anyone figured out a solution? My monitor indicator light is currently Purple. On is usually Blue, off is usually Red. One day it just stopped working and that's all I get. I am lost for any solution. I've searched for days for people with this similar problem but it is rare. Can anyone help? Thank you.

[retiredcaps]

Re: Sceptre X20WG-Naga inverter problems

Can anyone help?

The standard procedure here is to post clear focused pictures of all your boards (2000x2000 resolution) using the manage attachments functions so the pictures are attached to this forum. Please do not post inline because it slows down the loading of pages.

After you have posted the pictures using manage attachments, we can suggest test points, but you must have a multimeter.

[FreshPancakes]

Re: Sceptre X20WG-Naga inverter problems

Thank you for responding so quickly. I've uploaded pictures from my monitors motherboard. Nothing looks fried or altered. I'm puzzled.

[PlainBill]

Re: Sceptre X20WG-Naga inverter problems

Thank you for responding so quickly. I've uploaded pictures from my monitors motherboard. Nothing looks fried or altered. I'm puzzled.

Multiple problems, any of which make me want to scream in frustration.

1. I see a power supply / inverter. There is a connector at the upper left corner that MAY have a legend identifying the pins. That legend is unreadable.

2. I see a board on the right that appears to be an input board, with cables running everywhere. I don't see where those cables go.

3. The is no sign of a signal processor board.

Identify the pins on the connector in the upper left. With the power cord plugged in, measure the voltage from ground (the mounting screw near that connector) to each pin on the connector.

Provide a clear picture of the signal processor card.

PlainBill

[retiredcaps]

Re: Sceptre X20WG-Naga inverter problems

I'm not saying this will solve your problem, especially without seeing the voltage measurements as suggested by PlainBill above, but the Samxon GF caps are a problematic series.

Samxon makes good caps, but the GF series fail often without signs of bloating.

So do the voltage measurements first. If they look okay and we have exhausted all other alternatives (checking the voltage regulators, etc), then I would suggest replacing all the Samxon GF caps.