Norcent LT-3250 has power but screen is dark

[woaimi]

I initially created thread about this tv set with nothing on when plug in. It was diagnosed, with all the helps from this forum, to have a bad power supply. It has been collecting dusk until I found a PS to replace.
Now I have the set power on with red indicator as it plugs in and turns green as the ON button is pressed, but nothing on the screen at all. I checked the all PS output connectors and they all seem to have the correct voltages, except the Power_On is 4.5V instead of 5V like the board's legends suggested. I can hear the noise from the speakers but that's about it. All smd fuses on the inverter board tested good but I have not check to see if any voltage present at the inverter board, will do that later tonight.
Where do I go from here? any suggestion? thank you all very much. I will post some photos later as well.

[Clydeuk]

Re: Norcent LT-3250 has power but screen is dark

Check for voltage at the inverter, should be 24v supply (at the fuse you mentioned). If that's present check the BL-ON signal to the inverter. If that's there chances are you have an inverter fault. Do you get any light at switch-on from the backlights?

[woaimi]

Re: Norcent LT-3250 has power but screen is dark

thank you for the inputs! I'll be sure to check that when I get home. As for the screen, no light what so ever. I tried the flashlight method too but see nothing.

[Clydeuk]

Re: Norcent LT-3250 has power but screen is dark

You should have 24v supply, 3+ volt at BLON or whatever they call it on this. It's pointing to an inverter fault though not sure why you don't see anything on screen when you light it externally. It can be very hard to see though, I find having a menu on or analogue snow makes it easier, of course assuming the tv doesn't blank the display on no signal.

[woaimi]

Re: Norcent LT-3250 has power but screen is dark

I checked the fuses on the inverter board and they were all registered 24v on both ends of the fuses. The Bl_on is 3.2v when the set is off, and 0v when press ON. Also the standby voltage ON/OFF is 4.5v when off and change to 0v when power on.
Does that mean the inverter board is gone?

[woaimi]

Re: Norcent LT-3250 has power but screen is dark

any suggestion? looks like I have one of those rare brand to work with, couldn't find much information about it.

[woaimi]

Re: Norcent LT-3250 has power but screen is dark

whew!!! I finally able to get some work done for the tv set.
I took the whole thing apart to take some photos, it was probably 1 of the very early LCD, there were so many different board and one mounted on top of the others. Anyhow, after I put it back together decided to power it up for some voltages measurement. The red LED turns blue as power button pressed and I can actually see the screen with flashlight. The PS connectors provide the right voltages as the legend printed on board.

CN902 1-2-3-4-5 = GND
CN902 6-7-8-9-10 = 24V

CN903 1-2 = 12V
CN903 3-4-5-6 = GND

CN904 1 Power ON/OFF = 4.5V
CN904 2-3-4 = GND
CN904 5-6 (5.1V)= 5V
CN904 7 (5VSB)= 5V
CN904 8-9-10 = GND
CN904 11-12 = 12V

I've got 24V at either ends of the inverter fuses and also 3.2V at BL_ON on the inverter board.
does that mean the inverter board is the problem now? I will swap out the caps on the inverter just for the heck of it.
Any suggestion please! thanks

[budm]

Re: Norcent LT-3250 has power but screen is dark

Do you get 24vdc at both end of the small black fuse with '20' marking on top and F 1A/76V next to it by the connector? That is the common failure on CMO inverter board

[tom66]

Re: Norcent LT-3250 has power but screen is dark

I wonder why the bottom 8 FETs have appeared to run much hotter than the top 8 FETs. There's a very distinct change in colour between the two sides. Very odd.

[budm]

Re: Norcent LT-3250 has power but screen is dark

He may have to replace those filter caps on both sections of the board due to high AC ripple.

[woaimi]

Re: Norcent LT-3250 has power but screen is dark

Lol...once again, it's proofed that nothing can be compared with experience. That fuse that you mentioned is probably the problem. I put my meter in 200 range and got a 1 on the display. I guess next task is to find replacement. I supposed digikey should have it available.
Thanks

[budm]

Re: Norcent LT-3250 has power but screen is dark

I use PICOII fuse which has two legs. Higher voltage rating is OK. Make sure to replace those caps at the same time.

[woaimi]

Re: Norcent LT-3250 has power but screen is dark

I use PICOII fuse which has two legs. Higher voltage rating is OK. Make sure to replace those caps at the same time.

Bubm, would this fuse work? It's PICO 1A 125V.
http://www.digikey.com/product-detai...963314?cur=USD

thanks again

[tom66]

Re: Norcent LT-3250 has power but screen is dark

It's an obsolete part, you won't be able to buy it.
This you can actually buy:
http://www.digikey.com/product-detai...3CT-ND/3306914

[woaimi]

Re: Norcent LT-3250 has power but screen is dark

It's an obsolete part, you won't be able to buy it.
This you can actually buy:
http://www.digikey.com/product-detai...3CT-ND/3306914

Woohoo! just placed an order for a dozen. Thanks Tom66

[woaimi]

Re: Norcent LT-3250 has power but screen is dark

updating....
Thanks everyone for all helps! That fuse does the job nicely. I went ahead and replaced the small caps as suggested.

[tom66]

Re: Norcent LT-3250 has power but screen is dark

Thanks for the repair feedback.

[budm]

Re: Norcent LT-3250 has power but screen is dark

Glad to hear about the repair.

[ajmcello78]

Re: Norcent LT-3250 has power but screen is dark

Woohoo! just placed an order for a dozen. Thanks Tom66

Was the problem on the power supply? I just replaced mine with a pull from ebay that I paid $80 for. It worked fine for a month.

The original problem with the bad PS was that it turned on and the light was green for 3 seconds then turned off (back to red).

With new PS, it worked great! Fast forward 2 months.

Now the TV turns on, green light stays on, and a blue screen appears for 3-5 seconds then goes black. Light stays green. Is it my power supply or computer/ECM board?

Did yours have the blue screen problem? If so it might be this same problem that you ordered a dozen off. Have any left?

Thank you in advance.