Celcus DLED32167HD Dim Backlights - Sound but no Picture

[sickboy]

I have the TV in the title which uses common Vestel chassis with 17IPS11 PSU and 17MB55 main board.

When the TV switches on it gives a blank screen with normal backlight brightness (but no picture content) for maybe 2 seconds, then the backlight goes quite dim, but definitely still on. Sound works as normal.
There's nothing on the screen at all when you shine a bright light onto it.

The strange thing is that voltage on the backlight positive pin stays constant at around 85v whether bright or dim, the negative pin is around 30v - is this normal?

Can anyone give me any pointers on how best to tackle this?

[sickboy]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Tried freezing the eprom but it made no difference

[nomoresonys]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Check tcon fuse, see if you have voltage on each side, negative probe on chassis ground positive on each side of fuse.

[sickboy]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Check tcon fuse, see if you have voltage on each side, negative probe on chassis ground positive on each side of fuse.

Appreciate your help. I've got -12v DC either side of the fuse, that's minus 12v. Is that normal?

[budm]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Appreciate your help. I've got -12v DC either side of the fuse, that's minus 12v. Is that normal?

What did you use for GND? It cannot be minus reading, you probably has the Test probes connected wrong on the meter or on the tested end, etc... but at this point it is more likely that you do have +12V feeding the T-CON board.

[sickboy]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

What did you use for GND? It cannot be minus reading, you probably has the Test probes connected wrong on the meter or on the tested end, etc... but at this point it is more likely that you do have +12V feeding the T-CON board.

I'm an idiot lol
You're correct, I had the test probes in the wrong way round at the meter end..
12v DC on the TCON board

[budm]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Can we see the pictures of the T-Con board?
Does it have two ribbon cables between T-CON and the LCD panel? If it does then try having one ribbon cable connected one at a time to see what you see on the screen.

[sickboy]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Big wide tcon board Budm, looks like it's directly bonded to the screen via one wide ribbon... so it's safe to say if the tcon board is at fault the set's a scrapper

[budm]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Oh, it has integrated T-CON board, you can check the resistance of the MLCC (Muti Layer Ceramic Cap) to see if any one of them shows low resistance readings.

[sickboy]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

I can get the main board for this model (and screen number) on eBay for £14, is it worth a try? Or do you think it's most likely a tcon problem?

Edit: oops never saw your previous reply there, I'll try and find these MLCC devices and report back.

[sickboy]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Ok, I wasn't quite sure which of the SMD caps you meant, but I tested all of the larger smd caps on the tcon but none had low resistance.

Here's some close-ups of the tcon if they help.?

[budm]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Check them all.
I also see some Voltage test points that you should check, I.E. VCC, VSS, VCOM, etc....

[sickboy]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Ok, test points as follows:

VDD1 = 0.58V
VDD1L = 0.58V
VSS = 0.8V
V0FFE = 0.2V
VCC = 0.58V
F_VCOM = 0.1V
V0NE = 0.0V
VCOM = 0.58V
F_VCOMR = 0.58V

I have to go out for the rest of the morning but when I get back I'll check some more components with power off. There a few diodes and plenty of resistors with a zero on them to test.

[sickboy]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Well, nothing out of the ordinary found after some cold testing.
Could it be firmware causing this? I still have the option of buying a used mainboard - to rule it out if nothing else.
Other than that I think I have to assume the tcon board is faulty, and as it's bonded to the screen I'll probably just save the power board and main board then bin the rest.

[nomoresonys]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Your call, you could try the mainboard, suppose you could resell it if it isn't the issue.

[budm]

Re: Celcus DLED32167HD Dim Backlights - Sound but no Picture

Ok, test points as follows:

VDD1 = 0.58V
VDD1L = 0.58V
VSS = 0.8V
V0FFE = 0.2V
VCC = 0.58V
F_VCOM = 0.1V
V0NE = 0.0V
VCOM = 0.58V
F_VCOMR = 0.58V

I have to go out for the rest of the morning but when I get back I'll check some more components with power off. There a few diodes and plenty of resistors with a zero on them to test.

You sure do have problem on that integrated T-CON board based on those Voltage readings. You may want to trace out the VCC line to see why it is so low, typical VCC will be 1.8V, or 3.3V.