Double check my diagnostic logic on this LE55FHDF3300Z

[Pioneerx01]

I got my hands on LE55FHDF3300Z. It power on, back lights come on and stay on, but the display is blank (black). I get no splash sound, but I am not sure if there even was one. I pressed volume up, and blindly surfed the channels to see if I get static, but nothing.

Power supply board checks-out. I checked tab-bonds on panel, and they seem OK. T-Con however is registering only 0.33V on the fuse (fuse is OK). This leads me to believe that the main board is defective, since T-Con gets its power form main, and power supply checks out.

Thoughts?
Could I be over looking something? Should I try something?


Secondary Question:
The main board number is 40-RSC803-MAD2HG and Part Number is 08-SS55DFN-OC401AA. Only one selling it is ShopJimmy for $125. I have found one on eBay (under $50) same board number, but part number is 08-SS48DFN-OC400AA from LE48FHDF3300Z. They look identical, with same board numbers, but different part numbers because of the screen size? How likely is it that they are interchangeable?

Thanks
-Peter

[Pioneerx01]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

Anyone?

[budm]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

You are corrected that the T-CON is not getting the power, there should be a switched MOSFET for supplying the power to the T-CON, it is turned on by the processor of the main board, you just have to locate it, it should be near the LVDS power pins. BUT, the power can also comes from the power supply board from the pin named PANEL_PWR IF that is the setup on this TV, but we not know since we do not see any pictures of the boards.
So, any good clear pictures of you boards and the whole back sides of the TV?
As always, good clear pictures are always needed for us to help any one that wants to troubleshoot the problems.

[Pioneerx01]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

Pretty pictures I can do. See attached or more in dropbox gallery.

The power supply consists of two ribbon outputs. Top one (black) goes to secondary PSU that controls LED back lighting, that works just fine. Voltages are nominal as well. Gray/red one (dual row) goes directly to main board and the voltages check out as well. This PSU does not seem to generate +12V directly, odd.

I believe that the two left most cables (red cables) on the T-Con cable, should read +12V, but they register ~0.33V (green dots in pictures). These two cables lead directly to pins 1 and 2 on main board and they too read ~0.33V. Main board also has pin 39 which has no cable connected to in, but it reads +12V, so that leads me to believe that +12V voltage regulator is OK.

Thoughts?

[budm]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

OK, you need to trace the copper traces that are connected to the 2 pin of the LVDS red wires to see if it goes to the Q404 or U501.
It looks like it goes to the Collector (Drain) of Q404 (middle leg), that Q404 looks like it got hot, the top leg (Emitter/Source) should have 12V.

[Pioneerx01]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

The pins are connected the the top leg of Q404, but I found no connection (via continuity testing) to U501. And yes Q404 does look slightly toasted, I am not sure why I missed that.

As I was testing the voltages and touched the output on Q404 the TV came back to life. However it is all in nice shade of red and pink (or maybe light purple, what do I know, I am a guy). I hooked up my laptop to it via HDMI, but all I got was "no signal" message floating in sea of pink. And yes I did check the color settings. I can't get any image besides TCL splash screen and menu.

Looks like there is more damage to the main board that faulty voltage regulator (or is that a transistor?). Is it something I would be able to do myself, or it is easier to get a new board? I know how to solder, but replacing that Q404 would be somewhat challenging for me just due to size and proximity to other components.

Thanks for your help.

[budm]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

The transistor may have been damaged due to over load due to problem in the T-CON or the panel, or the transistor is under rated. But if you have Voltage on the fuse now and the pictures are bad then you have more problems.

[Pioneerx01]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

The transistor is now gone for good I can no longer get it to power up. While it was temporarily working I was getting "image" on the panel in terms of splash screen logo, menus, volume,... Even though I did not measure voltage in T-Con fuse it had to be getting +12V for something to show up.

The screen itself was showing only red, pink, purple and white. When laptop was connected to HDMI (1 or 2) laptop did not even recognize it was plugged in. When I forced video output through laptop's HDMI, the only thing I got was the "no signal" floating on the screen of the TV.

This leads me to believe that at least the main board is defective, which is a $130 replacement. T-Con is relatively cheap (~$25), but if it is the panel that went south, none are worth the investment to see if they fix the problem, as I will not be able to re-sale them back any time soon.

I think I am just going to scrap the TV for PSU and stand and call it a day. Investing in new main and T-Con is $160 which may or may not work if the panel is defective.

Any last thoughts?

[budm]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

That is a lot of money for the main board, you can bypass the transistor by connecting the Collector (Drain) to the Emitter (Source) to test what else is bad on the board.

[Pioneerx01]

Re: Double check my diagnostic logic on this LE55FHDF3300Z

That is what I actually did to continue further. Honestly I am not sure I am electronically qualified/experienced to do an "exploratory" surgery on the main board to find more bad components. Just jumping the emitter and collector was a nerve wracking task for me.

Problem one is that I am still having issues getting picture from HDMI ports, nor does the laptop see the TV as connected.

I technically have the RGB working on the panel, as the phrase "no signal" is white, so RGB has to be on to get white. TV is just interpreting black by turning on red and red/blue (purple) parts of the pixels, which is problem two.