Westinghouse LD-3255VX Right LED issue

[Kg74]

Hello: As the title says I have acquired a Westinghouse LD-3255VX for free with the issue that the right LED (looking at it from the front) will not illuminate. I have narrowed the issue to the Main board. It is not the LED strips. How do I know (I think), I swapped the LED cables for the left and right LED strips and both LED strips will work if I source the output from the left output (CON2,CON19,CON1)). Other than the right LED channel not working, the TV works fine, but dim on the right side.

I have attached four pictures. 1) is of the left half of the board, 2) the right half, 3) a close up of what area I think is having issues and 4) the entire board.

Looking at the third picture "Close up", The cable connector labeled CON2,CON19,CON1 works. If I run either the left or right LED cable to this cable connector the corresponding LED channel will work. But if I try this with CON15,CON14 either of the corresponding LED channel will not work.

From this I deduce CON15,CON14 channel is out. In the picture I have the LED cable removed but showing for the bad channel.

Anyone want to provide some guidance on what and where I should try to get some readings? I can not source this board as they are not available.

Can I move the cable connector attached to CON15,CON14 over and resolder it to CON11 as a work around?

[R_J]

Re: Westinghouse LD-3255VX Right LED issue

If you did move the cable you might end up overloading the good led drive ic, why don't you trace the fault in the bad section, there is a pdf for the MC34844, which gives pinouts etc. You may get lucky and its not the ic thats bad?

[budm]

Re: Westinghouse LD-3255VX Right LED issue

https://www.badcaps.net/forum/attach...2&d=1513719527
1) Turn the TV off and leave everything all connected. Set the meter to 200V scale then keep the black probe of the meter on the chassis, red probe of the meter on D22 Cathode, then turn on the TV while watching the meter to see how high the Voltage goes up to and then wait 5 seconds to see how low it goes down to.

2)Repeat the same procedure as in step but this time put the red probe of the meter on the Cathode of D21.

3) Report the readings to us.

[Kg74]

Re: Westinghouse LD-3255VX Right LED issue

Thanks for the responses and suggestions.

I took the dimple side on the diode and wider white stripe on the board to be the cathode.

For the working side D21 I got 54.1V on Cathode and 18.8 on Anode.
For the nonworking side D22 I got 19.1V on Cathode and 19.12 on Anode.

D21 goes from about 50V to 54.1 where it settles when turned on.
D22 stays at 19.1 or so when turned on.

Thanks

[budm]

Re: Westinghouse LD-3255VX Right LED issue

So the boost converter circuit is not working in that bad section.
Need to get the spec sheet of that IC MC34844

[Kg74]

Re: Westinghouse LD-3255VX Right LED issue

Thanks - I have two questions now. Easy one first. I found the part on DigiKey, and they have an 80ma version.

Q1 -- If the current IC MC34844A chip is bad will this work? Just remove and replace (easier said than done)?

https://www.digikey.com/product-deta...AEP-ND/2508755

Q2 -- I have a working side and a non-working side and a pin layout. Can I use the input readings from the good side and expect the same input readings on the bad side? Continuing can I do the same with all the other outputs.

Basically how can I isolate it is the IC MC34844A that is bad and not something else?

[budm]

Re: Westinghouse LD-3255VX Right LED issue

We know at this point the Boost converter section is not working, so check the RESISTANCE of D22 in both direction to see if it has low leakage resistance or not.
Then also check the EN signal to see if it is getting the command signal or not.
You can also do resistance comparison reading between the good and the bad section.
It is important that you read that spec sheet of the IC since it explains how it works, otherwise you can replace the IC or the whole board instead.

[Kg74]

Re: Westinghouse LD-3255VX Right LED issue

Thanks budm. I ordered two new chips as I blew shorted/out the good one while trying to test pin 7 EN signal. A little too small for my old eyes and not much space to work in.

At this point now nothing works.

I will update when the chips come -hopefully success - although with my lack of skills it may be an exercise in futility.

[Kg74]

Re: Westinghouse LD-3255VX Right LED issue

I am back and the MC34844A replacement was not a success. I managed to mangle the board pretty good in the process and lost a few pads.

I have attached a copy of the MC34844A Pin Diagram and have questions regarding Pin #32. These were some of the pads I managed to mangle on both sides. After looking at the board extremely carefully under my scope and probing all over the place I could not find where Pin #32 was suppose to go. I did not see any signs of a copper trace coming or going - it was like a "dead end" pin pad.

The Pin Diagram says:
"Pin/32 - Pin Name/VOUT - Pin Function/Input - Formal Name/Voltage Output - Definition/Boost output sense pin"

As I couldn't find anyplace the pin could go to as it appeared it was left blank, I left it without a pad.

One additional item - I read the diagram as if the logo and writing on the chips orientated the same way as the diagram. Is this correct?

Any ideas?

[dskall]

Re: Westinghouse LD-3255VX Right LED issue

You cannot rely on the writing for orientation of the chip. They will have some marking or indentation on one corner. Then you read pins counter clock wise

[Kg74]

Re: Westinghouse LD-3255VX Right LED issue

Thanks for the information. I have attached a photo of the chip on the board. The blue spot is the mark on the chip. The red numbers I drew in per your description.

I started Pin #1 on the bottom (of the photo by the blue dot) and went CC as you described so Pin 1-8 on bottom, 9-16 on right side, 17-24 on top and 25-32 on left side.

Is this correct?

In my picture 8-17 go to the LED connector which is consistent with what you say.

[dskall]

Re: Westinghouse LD-3255VX Right LED issue

Blue dot may or may not mark number one pin. Usually there is a physical mark. Usually round indentation or something permanent

[Kg74]

Re: Westinghouse LD-3255VX Right LED issue

dskall: Thanks - I put the blue dot there - it is where the chip had the indent. Looking at the LED outputs I am confident I have it orientated correctly and am counting correctly per your original post. That did help.

I tried replacing the EEPROM and that did not help. I followed all the traces back to the component and measured for continuity and/or shorts. All passed so I think I have the MC34844A chips installed correctly.

So backing up to the BUDM's first suggestions I measured voltage on D21 and D22 per BUDM's original response. Unlike before I only get 19V on both anode and cathode - both sides D21 and D22. Before I had 54V on the working side of D21 so my short circuit mistake blew something else out I think besides the MC34844A chip - which had a nice chunk blown out.

Question 1: the readings of D21 and D22 are "pre" or "post" MC34844A chip. If post, maybe I ruined the MC34844A chips when I installed them??

Question 2: Any other ideas of what I can test - I am no EE, but I have "skills" like Napoleon Dynamite.

[Kg74]

Re: Westinghouse LD-3255VX Right LED issue

Update: The TV is working, but I now have a bright spot on the bottom center right side. It was not there before so I think my LED string is not the issue. As previously posted only the right side was originally working and my mishaps began when I tried to replace U6 which controls the left side per suggestions.

Backing up as the path to working has been long. As I destroyed the first Main Board and couldn't source another I purchased one for a 26" set from ShopJimmy. I have attached a picture also from ShopJimmy. The main boards are 95% the same. All I had to do is take out and/or move some SMD components and add a channel. This included moving over all of the missing components, removing some that were not on the original Main Board, and adding an MC34844A (U6) which was not present on the 26" main board. I also swapped the EEPROM and one or two other items. In the end the new modified Main Board is the same per my visual inspection.

TV works, but as mentioned above I now have a bright spot on the bottom center right. This was not there when I started. Note my theory is this is most likely related to U4 (MC34844A) and not its sister chip U6. U6 which I added is working fine visually.

U4 is the original chip off the 26" board while U6 is a new chip I bought from Digi.

Question #1: Is it likely my issue is the original U4 from the 26" board is programmed for a 26" set? Are these chips programmed or are they run in default mode with certain added components used to manage the circuit?

Attempting to read the MC34844A data sheet I see mention of issues if channels are on that should not be. As the original U4 ran both L and R LED lines off one MC34844A, rather than two MC34844A chips like the 32" board; could this be the cause of my issues?

Question 2: Can I reset U4 without removing the U4 chip so it would be the same as U6, which appears to be working fine? U6 is "stock" while U4 may be programmed???

And to answer questions of future users - no the 26" board did not work plug and play out of the box.

[dskall]

Re: Westinghouse LD-3255VX Right LED issue

Can we get picture of problem?

[Kg74]

Re: Westinghouse LD-3255VX Right LED issue

Thanks for the reply. The Westinghouse Logo on the Bezel is the screen's center. In the picture you can see how the temperature 35 is brighter than 25 and how it also bleeds into the 4 in 40. It goes up to the Sun symbol.

And yes Minnesota is going into a heat wave later in the week.

[dskall]

Re: Westinghouse LD-3255VX Right LED issue

Hard to tell. To me looks more like a dark spot