TECHNIKA LCD26-207 Sound but no (black) picture... advice please.

[Markie76]

Hi Guys,

Firstly I'd like to say this seems like an excellent friendly and helpful forum and I'd like to say Hi to everyone.

I wonder if you can help diagnose the problem with my Technika 26" LCD TV.

The tv is a Technika 26-207 26" HD Digital TV.
The problem is there is sound on all inputs but no picture (screen is black - backlight is on). You plug it in and turn on the power, the blue standby led illuminates and when you power it on the led goes out and the screen remains blank (black) with backlight bleed around the sides. You hear the sound as you cycle through the inputs analogue, digital, scart, hdmi - no picture or OSD on any.
None of the capacitors are bulging, burst or distorted. No components visually look burnt out or damaged.

This tv has generic Vestel boards inside:
PSU: 17pw22-4
MAINBOARD: 17mb12-2
DIGITAL CAM PCB: 16mb1300-1

PICTURES

01 to 14 - pics of tv and pcbs. a)the purple screen pic 02 is the result of night mode - it is actually black with backlight poking through and around the edges. b)pic 07 - the black socket is where the hdmi socket pcb plugs into - took it off for pic.
x1 to x13 - random pics of caps etc...
mainpcbcapmod - a cap soldered and glued to the pcb, have seen a few hits on google suggesting this is vestel factory 'hash' and not a repair.

Have tried to be comprehensive as I'd like to save this tv because I like it

Happy to answer any questions or provide further info.

Thanks,

Mark.

[Rulycat]

Sounds like caps. There's a whole host of dodgy brands in there - HEC, G-Luxon (actually Teapo), Chong, Lindecon (who?) I'll let someone more qualified answer properly, but they're definitely suspect to me.

[Scenic]

could be a t-con issue. (fuse blown? no voltage going to the panel?)
bigger LCD panels used for TVs are usually black when off (opposite to computer LCDs, which are white when off)

you could confirm this via the LCD panel's datasheet

[Markie76]

Originally Posted by Scenic

could be a t-con issue. (fuse blown? no voltage going to the panel?)
bigger LCD panels used for TVs are usually black when off (opposite to computer LCDs, which are white when off)

you could confirm this via the LCD panel's datasheet

Hi,

by t-con - do you mean the LVDS pcb on the back of the LCD panel?

I've tested the smd fuse marked 'P' and its fine - the voltage coming out of it is 5.23v - so assume that pcb is getting power

[momaka]

Originally Posted by Markie76

by t-con - do you mean the LVDS pcb on the back of the LCD panel?

Yes, that should be it. The t-con could still be bad without blowing the main fuse. Therefore, post a picture of it - there are a few voltages that need to be checked.

[Markie76]

Originally Posted by momaka

Yes, that should be it. The t-con could still be bad without blowing the main fuse. Therefore, post a picture of it - there are a few voltages that need to be checked.

Pic below.

Its got 260W2C4LV1.6 on it

[momaka]

Okay, there are two voltages I'd like you to measure.

1) Measure the voltage between test point VDD_2.5 and ground. It should be 2.5v. Using your picture as a reference, test point VDD_2.5 is located close to the lower right corner of that Samsung chip on the right side of the t-con board.

2) Measure the voltage between test point AVDD and ground. AVDD is located all the way on the left side of the t-con, next to those big ceramic capacitors (C378, C379... etc.). I reckon AVDD should be 10V or more. Let me know what voltage you get for it, though.

It seems that the left side of the t-con handles all of the power, so that would be the area of most interest to us. Therefore, it may also be helpful to get the part numbers of IC320 (?), IC13, and that other IC above IC13. If possible, please post another (overhead, not angled) picture of the left side of the t-con. My guess would be that IC320 is the main controller for the t-con's power supply - hopefully one of those "smart" controllers (they have good datasheets ).

[Markie76]

Originally Posted by momaka

Okay, there are two voltages I'd like you to measure.

1) Measure the voltage between test point VDD_2.5 and ground. It should be 2.5v. Using your picture as a reference, test point VDD_2.5 is located close to the lower right corner of that Samsung chip on the right side of the t-con board.

2) Measure the voltage between test point AVDD and ground. AVDD is located all the way on the left side of the t-con, next to those big ceramic capacitors (C378, C379... etc.). I reckon AVDD should be 10V or more. Let me know what voltage you get for it, though.

It seems that the left side of the t-con handles all of the power, so that would be the area of most interest to us. Therefore, it may also be helpful to get the part numbers of IC320 (?), IC13, and that other IC above IC13. If possible, please post another (overhead, not angled) picture of the left side of the t-con. My guess would be that IC320 is the main controller for the t-con's power supply - hopefully one of those "smart" controllers (they have good datasheets ).

Yes, sorry for the angled pic it was a tight squeeze for the large camera without stripping the unit down further. Aerial pic attached below.

1. VDD_2.5 = 2.48v
2. AVDD = 4.79v
3. IC320 = 7585AIL B530KPW - Z
ICT3 = 24C64WP K535B
ICT5 above ICT3 = P 2042AF

[momaka]

Originally Posted by Markie76

Yes, sorry for the angled pic it was a tight squeeze for the large camera without stripping the unit down further.

Oh, no problem. It's actually still quite a decent pic. Believe me, I've seen much much worse. The one you just uploaded, though, is perhaps one of the best-focused pictures I've seen. Makes things much easier to analyze.
On the TV matters:

Originally Posted by Markie76

1. VDD_2.5 = 2.48v
2. AVDD = 4.79v
3. IC320 = 7585AIL B530KPW - Z

1. VDD_2.5 is fine.
2. AVDD is too low, however. Should be 10v or more. 4.79v suggests either something is pulling AVDD low (faulty component) or IC320 is not turning on/detecting a fault.
I think the simplest way to check this is to turn on the TV and see if any components in that area of the t-con get hot (most probable candidates for this are IC320, diodes SD1, D7, D8, and transistors Q3, Q4, and Q5). You can use your finger for this (don't worry, there are no high-voltages on the t-con, but do be careful not to get burned, since a faulty component can get pretty hot) - I know this method is not very scientific, but it's effective. You might need to cycle the TV ON/OFF a few times to do this, since IC320 may shut down if it detects a fault.

Speaking of IC320, I did find a datasheet for it based on the numbers you posted - it's a Intersil EL7585A and can be found here:
http://www.intersil.com/data/fn/fn7523.pdf
It is a "smart" controller, indeed - makes things a lot easier to understand in the circuit. I'm still analyzing it though.

[Dgtech]

Forgive me but I'm simply trying to get through all the clutter of this TV set. Wow. I mean, if you search around other TV's they are mostly a little bit organized. Theres a lot of stuff going on with wires everywhere.

Anyways, I think there is an inverter board underneath the metal cage. This cage is located to the left hand side of pic number 3. I have a feeling that this may be where the problem resides.

[Markie76]

Originally Posted by Dgtech

Forgive me but I'm simply trying to get through all the clutter of this TV set. Wow. I mean, if you search around other TV's they are mostly a little bit organized. Theres a lot of stuff going on with wires everywhere.

Anyways, I think there is an inverter board underneath the metal cage. This cage is located to the left hand side of pic number 3. I have a feeling that this may be where the problem resides.

Correct, the inverter is under the metal cage the electronics are mounted on.

Whats your theory re the inverter?

It seems to be working ok as the backlights come on fine

[Markie76]

Originally Posted by momaka

I think the simplest way to check this is to turn on the TV and see if any components in that area of the t-con get hot (most probable candidates for this are IC320, diodes SD1, D7, D8, and transistors Q3, Q4, and Q5). You can use your finger for this (don't worry, there are no high-voltages on the t-con, but do be careful not to get burned, since a faulty component can get pretty hot) - I know this method is not very scientific, but it's effective. You might need to cycle the TV ON/OFF a few times to do this, since IC320 may shut down if it detects a fault..

Using my test finger I didn't find anything even warm anywhere on the LVDS pcb.
I rechecked the two test points and they were getting voltage as before - I also cycled the power 10 times and still nothing was warm

[Dgtech]

OK sorry, I read the symptoms wrong.

[momaka]

Originally Posted by Markie76

Using my test finger I didn't find anything even warm anywhere on the LVDS pcb.
I rechecked the two test points and they were getting voltage as before - I also cycled the power 10 times and still nothing was warm

Sounds as if the controller IC320 is not turning on or it's detecting a fault. To verify if this is true, measure the voltage on the following pins of IC320:
Pin 18 (EN)
Pin 14 (VREF)
Pin 20 (PG)
Pin 16 (FBB)
Pin 6 (FBP)
Pin 8 (FBL)
Pin 11 (FBN)
Use the Intersil EL7585A datasheet I posted above as a guidance - page 1 has a diagram of the pin outs. For each pin, measure the voltage between ground and that pin. For pin EN, VREF, and PG, also see if the voltage on them changes or varies when you cycle power to the TV. Let me know what voltages you get.

Last but not least, with the TV turned off and unplugged, measure resistance between ground and each of the following test points: AVDD, VON, VOFF, and VDD. If your multimeter is manual ranging, use 2000 Ohm scale. Post what resistances you get.

*EDIT*
Just noticed and forgot to mention... Pin 1 on IC320 is right where that arrow points in the lower left corner. The pin count then increases counter-clockwise, as per the datasheet.

[762mm]

Hello everyone,

I have joined these forums because I'm kind of in the same boat as the OP and wanted to contribute a little of what I can. I recently acquired an unwanted 26" Samsung LCD TV (model LN-R2668W) which doesn't work. The TV turns on and stays on, but there is no picture or sound, just a black screen with the backlight on. Buttons on the side of the TV do not work (none of them) and the remote doesn't either. I know the TV is receiving a signal from the remote, because the red power led flashes rapidly when a button on the remote is pressed - yet nothing happens, the screen remains black with the backlight on (without any source or channel changes, etc).

After doing some research, I found out that the T-con board is usually the culprit in these cases (all my capacitors look perfect, by the way - no bulges, no leaks, no strange relay sounds when the TV powers on).

Now... I'm not very familiar with circuit boards, but have basic soldering skills. To be perfectly honest, I was planning on just waiting to find out what problem the OP reports and how he/she fixes it, then I would just attempt to do the same thing and hope for the best (lol!) - after all, when you're a newbie like me, you gotta start learning somewhere, right? I've already "bridged" the P fuse with solder hoping that was my problem, but nothing has changed. So I guess the fuse was ok all along.

In order to help a little bit with solving this issue, I am including a scanned picture of my actual T-con board (same one as the OP). Hopefully it will allow you pros to take a better look at it and maybe determine where the problem might be. Buying a used t-con is always an option, but the odds of getting another defective one are too great to even venture that way (cheapest I've found them online are 60$). New ones are no longer available, AFAIK... plus might not be worth the $, if you consider the price of newer (and larger) LCD TV's out there today.

[Dgtech]

Please dont post about a different set altogether in a dissimilar thread. Start a thread for Samsung - (model number) - That is, if there isnt one already. I'd do a search for that model number first. If you cant find a thread already started for it, then start a new one then copy and paste the last posting that you did here. It's ok, everyone's new once...... ONCE!!!

[762mm]

Originally Posted by Dgtech

Please dont post about a different set altogether in a dissimilar thread. Start a thread for Samsung - (model number) - That is, if there isnt one already. I'd do a search for that model number first. If you cant find a thread already started for it, then start a new one then copy and paste the last posting that you did here. It's ok, everyone's new once...... ONCE!!!

If you look at the T-Con board I posted, you'll see that it is the same one as the OP's and has the same symptoms. These boards were used in Samsung, Sony, Panasonic and MANY other 26" LCD TV's... and have the exact same problem.

I understand the rules of a forum, as I am not new to them... I am simply new to playing with circuit boards. Cheers!

[momaka]

Hi 762mm, welcome to the forums.

Your t-con does indeed look the same. As Dgtech suggested, though, it would probably be a better idea to start a new thread. There are several reasons for this:
1) It helps keep the forum organized. If someone has the same TV and same problem or has resolved this problem, they are a lot more likely to find your thread.
2) It's easier to answer questions. When there are two or more people who have supposedly the same issues and they all start to ask questions, the thread can get very confusing on who's doing what and what has been tried already. This leads to 3)
3) While your t-con and issues do appear to be the same as the OP's, that does not necessarily mean that the same components may have failed.

With that said, feel free to start a new thread. Make sure to put the brand and model of the TV in the title, as well as a short description of the problem. Then post the same description you have in this thread. A link to this thread may also be useful to other readers.

For starters, I would suggest you go through the same procedures that I posted for Markie76 (posts #7 and #14 above). Post the results in your thread.

[Markie76]

Measurements as requested;

On Voltage on the following pins of IC320:
Pin 18 (EN) - 0v
Pin 14 (VREF) - 1.22v
Pin 20 (PG) - 5.18v
Pin 16 (FBB) - 0.37v
Pin 6 (FBP) - 0v
Pin 8 (FBL) - 1.42v
Pin 11 (FBN) - 1.09v

Cycling the power;
Pin 18 (EN) - 0v
Pin 14 (VREF) - 1.22v
Pin 20 (PG) 5.17/5.19v

Power off & unplugged resistance;
AVDD - .755 (755 ohm)
VON - 25.1k
VOFF - 58.9k
VDD - 54.6k

Thank you for the effort you are putting in to help me with this

[momaka]

Originally Posted by Markie76

Thank you for the effort you are putting in to help me with this

You're welcome. I actually enjoy the challenge these t-cons present.

Originally Posted by Markie76

On Voltage on the following pins of IC320:
Pin 18 (EN) - 0v
Pin 14 (VREF) - 1.22v
Pin 20 (PG) - 5.18v
Pin 16 (FBB) - 0.37v
Pin 6 (FBP) - 0v
Pin 8 (FBL) - 1.42v
Pin 11 (FBN) - 1.09v

Okay, the good:
Pin 18 (EN) is the enable pin of IC320. When this pin has low voltage (less than 0.8v, as per EL7585A datasheet), IC320 is enabled to work, so what you got above is good.
Pin 14 (VREF) is the internal reference voltage of IC320. Datasheet indicates it should be between 1.19v and 1.235v. You have 1.22v, so that's also good.

Now the not-so-good:
Pin 20 (PG) is used by optional protection FET (not sure if there is one on your t-con). When IC320 detects a fault or when IC320 is disabled, this pin will have high voltage (usually 0.6v or more). Since IC320 is enabled as I described above, then there must be a fault on one or more of the voltage rails, AVDD, VON, VOFF, and VDD. Your measurements for FBB, FBP, FBL, and FBN seem to agree with this. When working, this is what they need to be:
Pin 16 (FBB) --------- 1.188 to 1.22v
Pin 6 (FBP) --------- 1.17 to 1.23v
Pin 8 (FBL) --------- 1.174 to 1.226v
Pin 11 (FBN) --------- 0.171 to 0.235v

So what all of this means is that there is likely one or more bad components on voltage rails AVDD, VON, VOFF, and VDD. My guess would be either a bad ceramic capacitor somewhere or a shorted diode or transistor. Not likely to be a resistor, though.
With that said, let's start with the easy things first: Using your multimeter (either diode/continuity test or resistance @ 2000 Ohm scale) to check diode SD1 (next to inductor L1). When negative (-) probe is on cathode pin of SD1 (side marked with a stripe) and (+) probe on the other, you should get lower resistance/voltage drop than when you reverse the probes. Nothing less than 50 Ohms/ 0.05 voltage drop, though. If you do, let me know.

Otherwise, if SD1 checks out fine, the next step would be to check some of the ceramic capacitors in the area (compiled list is at the end of post). The good thing is, you can check them without removing them from the t-con. Just use your multimeter to measure the resistance across each. Start with 2000 Ohm scale. If any of those ceramic capacitors measures under 100 Ohms, write down the resistance and post it here. And if any of them measures less than 50 Ohms, definitely make note of it and post it here. The typical failure mode of a ceramic capacitor is short circuit (2 Ohms or less), but sometimes they can fail with a slightly higher resistance of 50 Ohms or less - just enough to disturb the whole circuit.

Now, you have already done a resistance test on voltage rails AVDD, VON, VOFF, and VDD, and the good news is, none of them appear to be shorted to ground. This means that the following capacitors have also been checked (therefore you do not need to check them again)
C378, C379, C380, and C381 (the big 4 ceramic caps by test point AVDD)
C386 and C387 (near test point VON)
C389 (next to VDD), CP3 and CP4 (above test point VDD2 and VDD3)
C388 (near VOFF)
C376, C383, C375 (the big ones connected to VIN, to the right of inductor L1).

Again, those capacitors I mentioned above have been checked already. That leaves just the other smaller ones. Starting at the top-left corner on the picture you posted and going left-to-right, top-to-bottom, these are the ones I think that need to be checked (I'll try to group them as much as possible):
CP2; CC17; CG18; CD28 and CD29; C403, C385, and CD24 (next to VON); CD30, CD31, and CD33 (above VDD); CT30; CD23 (next to diode SD1); CD27; CD26;
Note: you may need to rub the multimeter's test probes a little bit on each cap lead in order to get an accurate reading.
----
And that's pretty much it for now. Sorry for this big wall of text. Hope it helps somehow, though. Let me know if you have any questions.