Good backlight and "Toshiba" displayed on power up, then unresponsive

@jayeff my apologies about the model number, I thought I had the TV linked to the post. The TV is model number 65L5400U, its a 65in Toshiba.

I have tried both HDMI ports on start up, but I will test the other inputs today and get back to you.

On the ifixit page for the TV (model 65L5400U) I uploaded some images of all the boards and the TV manual. There are 4 buttons on the Main Board that correspond to Power, Volume up, Volume down, and Channel/Input (from top to bottom. Basically, none of those buttons do anything when pressed. After being plugged in, the TV boots itself up, displays "TOSHIBA" in red with a black background, then sits at a totally black screen with no display at all (backlight still on) I am unable to access menus, and no indication of volume level, channel number, or anything else is displayed.

I also purchased the exact components that were in the TV originally

I searched for the firmware, but was unable to find any.

Thanks for the input, and I'll get back to you ASAP!

@grant_mlack

My apologies to you.

I saw the device information and made a wrong assumption as a lot of posts here just pick the nearest device to what they have. I didn't notice that it was created by you, not even though you said it in your post. Again my apologies

No images or audio but with backlight makes it seems as though the mainboard has problems and has shutdown i.e no power or has not fully completed the power on boot process but you have changed both the power board and the mainboard

Did you change all the boards that you changed all at once or one at a time?

Have you tried swapping back original individual boards one at a time and checked? Not sure if this is good advice if there is a fault which is damaging a good board when it is inserted so that the fault is still there regardless.

As I said I don't know Toshiba so just trying to get a handle on how it works so that things can be tried to narrow it down.

Screen seems to work because logo seen OK, backlights work so LED driver board OK so presumably power board works OK for that, mainboard starts up displays logo then nothing not even audio so just not a video problem. Do you know the history of the TV?

@jayeff

Unfortunately i do not know the history of the TV. I picked it up for next to nothing and figured it would be a fun project to fix. Now I'm way too invested. It was in a storage unit for some time apparently. (I know I was asking for trouble haha)

Just tried all the inputs and no luck

I swapped out each board one board at a time and it was when I replaced the main board that the screen actually turned on, i.e. Toshiba logo and backlight.

Leads me to believe everything downstream of the mainboard is fine.

I have not gone back and tried the originals though. I'm going to do that right now. Might try the old psu with the new main board?

I just wish I knew more about what to look for on the main board. I trust my abilities with soldering and such, but when it comes to diagnosing the issue I'm just lost.

I feel like you might be right about the boot of the main board not completing properly, I just don't know how to test that.

-Grant

@jayeff

Just swapped boards around. Psu and all other boards (except the mainboard) seem to yield the same results between old and new.

Feeling more and more strongly about the Mainboard being the issue

I tested the test pins on the main board coming from the PSU and they all seem to have stable voltages at the correct values. I can add more photos if needed as well.

-Grant

Hi @grant_mlack

The board shown in the 2nd last image seems to be the board that all the testing is done on if you have the right test equipment and you know what you're testing for. It shows points such as TMS, TDCK, DEBUG, TCE and TCK but I have no idea what they mean or what they relate to, but the term "debug" is common when testing devices.

The LED driver board (assume that it the 4th image down) is the only one besides the power board that seems to have fuses on it so again no joy in testing the other boards for known voltages at specific points (although I note that you tested voltage to the mainboard OK.)

Can only think that you could try checking the cables between the boards for continuity of each wire in case of fracture or even corrosion in the ends that connect.

That's about all that I can think of at this stage, that you haven't also tried.

Sorry I don't think that I know what to try next that may help you.