JVC 49cf890 - Fire TV - no picture but sound

[Dobsuk]

Hi everybod. I've got that kit now JV LT-49CF890. It is been a working and just black screen while they were watching tv. So, it looks the backlight is working as i can see it working when switch the tv on, i can hear and the sound from the menu. I think it is already in factory settings. Any suggestions before to proceed with disassembling guys? Some tricks or ideas what to look for when remove the back cover? Thanks.

[Dobsuk]

Re: JVC 49cf890 - Fire TV - no picture but sound

Tadaaaa... no T-CON board or not in the way i expected to see

Nothing changed if i disconnect the ribbon cable from the main board. Nothing changed if i tap on the ribbon cables connected to the display. So, shall i buy new main board or maybe the fault is in the board attached to the screen?

[vinceroger69]

Re: JVC 49cf890 - Fire TV - no picture but sound

on the power supply is ther a pin that says bl-on or somethink like that as thats the back light on voltage what voltage is on that pin when tv fisrt switched on and when just a black screen.

there is a repair kit for these boards with no backlight issue these are the parts too check
Q17
U9
D27
R78

[Dobsuk]

Re: JVC 49cf890 - Fire TV - no picture but sound

Backlight is working. I can see it when i switch the tv on.

[vinceroger69]

Re: JVC 49cf890 - Fire TV - no picture but sound

Backlight is working. I can see it when i switch the tv on.

sorry missed that bit,
have you checked the led strips incase a led is shorting under load.

[Dobsuk]

Re: JVC 49cf890 - Fire TV - no picture but sound

No, i have not checked the led strips as i thought it will be something about the boards if the backlight is working.

[vinceroger69]

Re: JVC 49cf890 - Fire TV - no picture but sound

No, i have not checked the led strips as i thought it will be something about the boards if the backlight is working.

my thinking was if a led is shorting out could it be putting the backlight circuit into protection mode, hopefully a more experienced member will chime in with suggestions.

[vinceroger69]

Re: JVC 49cf890 - Fire TV - no picture but sound

just read this post a lot of people are having issues with this tv model a lot of it seems firmware related too.
https://uk.amazonforum.com/s/questio...ith-everything

[Dobsuk]

Re: JVC 49cf890 - Fire TV - no picture but sound

Yeah, acording to this post this TV is piece of sh.t

[dskall]

Re: JVC 49cf890 - Fire TV - no picture but sound

Need to check if you have power on your t-con. Fuse good. Check for various voltages at test points.

[vinceroger69]

Re: JVC 49cf890 - Fire TV - no picture but sound

post 2 picture 3 under the ribbon cable connector there is a fuse marked N what votage do you get on each side of that one meter lead on metal tv chassis then test voltage each side.

[Ancient1]

Re: JVC 49cf890 - Fire TV - no picture but sound

Backlight is working. I can see it when i switch the tv on.

Briefly or ? You can see BL seeping through holes in the metal panel base, if you open the back of the TV.

Do you have Video ? if the Screen is black : press Menu button, so you know you (should) have an image, and use Flashlight on the screen to detect the faint image.

No Backlight : it works briefly and shuts down : Most likely dead LED is disconnecting the circuit : Buy new set ( using the Model printed on the Strips) , or , if you have same hue and brightness LED - Replace.

No Video : This is Main - Tcon - Panel line. Involves electronics Troubleshooting usually. Clean the LVDS connectors. Check that Main receives Power ( as printed on the PCB, near PSU-Main connector) by checking pins or detecting onboard. Check the T-con Fuse , Check Panel long boards .
According to results you can decide on electronics or new board path.

[Dobsuk]

Re: JVC 49cf890 - Fire TV - no picture but sound

post 2 picture 3 under the ribbon cable connector there is a fuse marked N what votage do you get on each side of that one meter lead on metal tv chassis then test voltage each side.

Thanks, will check this later. Anyway i ordered new main board as they were about 16GBP But will check and that fuse.

[Dobsuk]

Re: JVC 49cf890 - Fire TV - no picture but sound

Briefly or ? You can see BL seeping through holes in the metal panel base, if you open the back of the TV.

Yes, i can see the light through the holes

Do you have Video ? if the Screen is black : press Menu button, so you know you (should) have an image, and use Flashlight on the screen to detect the faint image.

No video.

[vinceroger69]

Re: JVC 49cf890 - Fire TV - no picture but sound

Thanks, will check this later. Anyway i ordered new main board as they were about 16GBP But will check and that fuse.

please keep us updated once the replacement mainboard comes be nice to see if it fixes the issue

[dskall]

Re: JVC 49cf890 - Fire TV - no picture but sound

My money is on a bad T-con. But there's a reason I don't bet.

[vinceroger69]

Re: JVC 49cf890 - Fire TV - no picture but sound

My money is on a bad T-con. But there's a reason I don't bet.

t con built into mainboard on these?

[dskall]

Re: JVC 49cf890 - Fire TV - no picture but sound

Still a t-con. True there not just board swaps, but can be repaired.

[dskall]

Re: JVC 49cf890 - Fire TV - no picture but sound

I believe the t-con is on panel strips.

[vinceroger69]

Re: JVC 49cf890 - Fire TV - no picture but sound

Still a t-con. True there not just board swaps, but can be repaired.

totally agree with you i would rather reapair a board than swap it out, in the past i have even brought a good board just too fault find mine, then resell the replacement with no money lost.