JVC lt-47x579 backlight comes on but nothing else

[JC1979]

Hey everyone. Hopefully someone out there can help with my tv.

It is a JVC lt-47x579 LCD television, about 3 years old. Yesterday I got home from vacation pushed the power button on the remote. The little blue light on the bottom left comes on and stays on constantly. And the screen lights up with a bluish glow, which I assume is the backlight(correct me if i am wrong) I tried unplugging. left it unplugged over night, same thing this morning. I tried the vol + menu + power button thing, and no luck.

Next I took the back off the tv to check for any fuses, could only find one and it was fine. I can't smell any burning, and the capacitors look fine in appearance.

I took a few pictures and will post the links to them in my photobucket account. If anyone could give me any advice on what to check next that would be great.

Thanks in advance.

Pic's

http://i73.photobucket.com/albums/i2...9/100_0128.jpg

http://i73.photobucket.com/albums/i2...9/100_0129.jpg

http://i73.photobucket.com/albums/i2...9/100_0130.jpg

http://i73.photobucket.com/albums/i2...9/100_0132.jpg

http://i73.photobucket.com/albums/i2...9/100_0133.jpg

http://i73.photobucket.com/albums/i2...9/100_0136.jpg

[tom66]

Re: JVC lt-47x579 backlight comes on but nothing else

The blueish glow is good, indicating the backlight is okay.

Please be careful with JVC TVs. A nasty trick some of their LCDs have is to include a photocell on the board which detects light. If the board is powered up with light (i.e. case off) it will erase encryption keys required for HDMI!! Not all JVCs do this but some do.

There is one more board in your TV on the top side of the screen. A cable probably connected to it. This is your T-con board. Can you remove it and take a picture of it? The T-con is responsible for the image displayed, and it usually has a fuse on it.

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

Thanks for the quick reply tom66,

Here is the board at the top of the panel. I couldn't see any fuses on it.

http://i73.photobucket.com/albums/i2...9/100_0141.jpg

http://i73.photobucket.com/albums/i2...9/100_0138.jpg

And thanks for the heads up about the possibility of that photocell, i will try and be careful from now on.

[tom66]

Re: JVC lt-47x579 backlight comes on but nothing else

Can you get a closer shot near the video connector (which goes to the main board.) I think I can see a fuse there...

Also disappointing to see a cheapie CMO LCD in a JVC... would have expected a Samsung or Sharp LCD at the price they charge...

The T-con says "42" on it; strange for them to use that in a 47" set...

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

Here is two pictures close up next to the main connector.

http://i73.photobucket.com/albums/i2...9/100_0150.jpg

http://i73.photobucket.com/albums/i2...9/100_0151.jpg

[tom66]

Re: JVC lt-47x579 backlight comes on but nothing else

FP1 is your fuse.

Make sure set is off (and unplugged.)

Set your meter to 200 ohms range.

Touch red probe to one end, black to the other. If fuse is good, you will see from 0.0 to 2.0 ohms. Don't confuse the "infinite" reading you get when the probes are not touching with 1 ohm... If the meter stays on the infinite reading, the fuse is probably dead.

If the fuse is blown, there could be a short, or the fuse could have just failed on its own (this sometimes happens.)

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

o.k. Well the meter I have is one of the digital clamp auto-ranging kind. I set it to ohms, put the leads on either side of FP1. The reading I got immediately said 13.1 then went right down to 2.0 then slowly crept down till it said 0.4 where it fluctuated between 0.4 and 0.3. Now im not sure if this is a normal reading or if it is a problem with my meter. I could try and see if |I can get a hold of a different one.

also my meter does have the beeping sound for continuity and it was beeping while on the fuse.

[ben7]

Re: JVC lt-47x579 backlight comes on but nothing else

o.k. Well the meter I have is one of the digital clamp auto-ranging kind. I set it to ohms, put the leads on either side of FP1. The reading I got immediately said 13.1 then went right down to 2.0 then slowly crept down till it said 0.4 where it fluctuated between 0.4 and 0.3. Now im not sure if this is a normal reading or if it is a problem with my meter. I could try and see if |I can get a hold of a different one.

also my meter does have the beeping sound for continuity and it was beeping while on the fuse.

Yeah, your fuse is good. The high reading at the beginning might have been from a bad/oxidized spot on your probes.

[tom66]

Re: JVC lt-47x579 backlight comes on but nothing else

Okay, now plug everything in and screw the boards down, and check the voltage on both ends of the fuse. It should be either around 5V or around 12V, probably the former.

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

screwed it all down, plugged all the plugs in, turned it on. I checked both sides of that fuse and got 11.58 both sides. I grounded to a screw in the frame.

[tom66]

Re: JVC lt-47x579 backlight comes on but nothing else

11.58V is quite low but probably high enough.

There is a voltage regulator on the T-con. If this fails it could cause issues. I've highlighted it in the picture attached.

To test it:
- Set meter to volts DC
- Place black probe in a spare screw hole in the metal frame of the TV
- Place red probe on each pin: pin 1, the tab pin at the top of the regulator, and pin 3. Note the voltage on each of the pins. Be careful not to short any pins together.
- Also note down the part number on the regulator for example LM1117-33.

When TV is on, can you turn it off using the remote control, or do you have to unplug it?

And, if you connect a source to, say, the composite video input and audio input, and flick through the inputs using the INPUT or SOURCE button, do you eventually hear any sound?

[tom66]

Re: JVC lt-47x579 backlight comes on but nothing else

Darn it I always forget the attachment! Gmail and Thunderbird remind me, vBulletin doesn't...

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

I don't see the attached picture, however I did just hook the tv up to my cable box with a hdmi cable. tried it in input 1,2, and 3. no sound. I verified that the box was on a channel with sound by hooking it up to another 32" lcd. And I can turn the tv on and off with the remote and the button on the side of the tv.

, ah, theres the picture. Will go test now.

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

the readings i get are.

the tab pin o.oo4v
the top pin 2.478v
the bottom pin 3.276v

I wasn't sure which was pin 1 or 3 so top is the upper most one in the picture you posted and bottom the lower pin. and the tab on the left.

this is with all the plugs connected and the set powered on..

the number on the reg is

AME8815
AECS250
0747

[RON_CET]

Re: JVC lt-47x579 backlight comes on but nothing else

Symptom:
After the TV is powered ON, no video appears and the blue power LED remains lit. If the
Signal PWB of the TV is heated prior to AC application to TV Power Supply, the TV set
powers ON and operation is restored upon AC application and TV Power ON.
Cause:
The Reset IC (IC2502) on the Signal PWB does not reset. There is not enough margin
between the Setting Voltage (3.1V) of IC2502 and the VCC (3.3V) of IC2502.
Solution:
Replace IC2502 (3.1V) on the Signal PWB with a (2.8V Reset IC type)

new part number for IC2502 is IC-PST8228U-W or S-80828CNNB-G-W

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

Hi RON_CET?

Thanks for the reply. However, if im being honest i really didn't understand all of what you said. I did understand that i should repace IC2502. first question, what and where is this? (i am aware that it was actually 2 questions.) next question, is there a way to test this or are you pretty sure thats the problem?

Im pretty handy with most tools, can read a meter pretty well. But i honestly dont have the experience with flat panel televisions to know what im doing without a little help.

Thanks.

[RON_CET]

Re: JVC lt-47x579 backlight comes on but nothing else

the ic2502 will be on your main cba which would be board with tuner / and your av inputs,this is actually a confirmed fix via JVC service bullentin
see attached ic2502 circled in red

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

Thanks for the info. I did a google search to try and find that part, but everywhere i have looked it comes up out of stock. Do you perhaps have any idea of a source for this part where it would be stocked?

[tom66]

Re: JVC lt-47x579 backlight comes on but nothing else

For testing you may remove the RESET IC. It is only to make sure the TV powers down nicely if power is suddenly interrupted (so it does not corrupt things like user settings.) It should be fine going to standby..

This issue has been seen on a few other TVs too.

[JC1979]

Re: JVC lt-47x579 backlight comes on but nothing else

Hi tom66,

So, if i remove ic 2502, what steps should i take to test it? Is it just a case of removing it then powering on the set? And do you by chance happen to know somewhere i can order a replacement if this is the problem.