Toshiba 43L3753DB Screen Issue

[Russ17]

Hi

I have a Toshiba 43L3753DB.

When turned on, the Toshiba Logo is distorted and unreadable, but once the TV is booted, pressing the "Menu" button gives a visible menu, but if you try to select any menu, the screen becomes unreadable. The No signal message is readable and so is the info bar at the bottom of the screen, it just seems that as soon as there is a requirement to provide an image across the entire screen, it becomes unusable.

When the screen is unreadable, the PSU noise increases.

The 12V is good (12.14V) and is present on the T-Con fuse.

On the 17IPS62 PSU, Diodes D23/24/25 have about 37.8V, but this reduces when the fault is present. Diodes D7/8/9 have 12.14V on the cathode. I have not performed a diode test on any of them as yet.

The LED back light voltage is 85V. but the back lighting does vary in brightness during boot up.

Does this sound like a PSU, Main board or Firmware issue?

Mainboard is 17MB110P.

I have PSU and Main board from A Toshiba 32L3753DB. The PSU has a smaller transistor in the HOT section, so probably cannot be used even as a test. The Main board is set up for a 32" screen, so can this be set to work for a 43" screen by flashing the firmware?

Any help and advice gratefully received.

Regards

Russell

[budm]

Re: Toshiba 43L3753DB Screen Issue

Show us the screen shots of what the picture looks like on the screen, then good clear pictures of the whole backside of the TV showing all the boards so we can see what we are dealing with.

[Russ17]

Re: Toshiba 43L3753DB Screen Issue

Dear Budm

Here are the requested pictures:

Splash Screen (Bad) This is what should be the TOSHIBA Splash screen at boot up

Menu (good) this is the initial display of the menu, which is correct, but when you select a menu item, the display goes (bad) with just lines.

The info bar displays "correctly", as does the "No signal" box.

When selecting "source", the display does not show the sources list, you just get lines.

The PSU is squealing quietly, at all times (but I have a similar Polaroid TV that does the same, with no ill effects) but when the screen fault shows, the PSU starts ticking.

Should the voltage at the Cathode of D23,24 & 25 be 37V? The schematics I have seen show it as 24V DC.

Regards

Russell

[Diah]

Re: Toshiba 43L3753DB Screen Issue

you can use the main boards from 32 screen... dont use the PSU its not fit with yours

[Russ17]

Re: Toshiba 43L3753DB Screen Issue

Hi Diah,

Thanks for the reply.

Does the Main board need to be setup with different firmware in order to be used with the 43" screen, as it is from a 32" screen version?

Any thoughts on the voltage on D23/24/25, on the PSU, as it seems to be too high, according to the schematic, which shows 24V?

Regards

Russ

[Diah]

Re: Toshiba 43L3753DB Screen Issue

Hi Diah,

Thanks for the reply.

Does the Main board need to be setup with different firmware in order to be used with the 43" screen, as it is from a 32" screen version?

Any thoughts on the voltage on D23/24/25, on the PSU, as it seems to be too high, according to the schematic, which shows 24V?

Regards

Russ

about main boards they share same firmware.. it will work just later need to write serial and size in service menu.

37V instate 24V ? are much high... i think you may have defect sound on the set ??? BTW i cant see the diode on yours photo... try upload high resolution photo of yours power boards.

[Russ17]

Re: Toshiba 43L3753DB Screen Issue

Hi Diah,

I will try the Mainboard. Would it work if the serial number and screen size did not get modified in Service menu>

I have attached a picture showing where I measured 37V, which according to the schematics, should be 24V.

Thanks for the information.

Regards

Russ

[Diah]

Re: Toshiba 43L3753DB Screen Issue

dont use your main boards now until you are sure the voltage you mentioned correct

[Diah]

Re: Toshiba 43L3753DB Screen Issue

Hi Diah,

I will try the Mainboard. Would it work if the serial number and screen size did not get modified in Service menu>

I have attached a picture showing where I measured 37V, which according to the schematics, should be 24V.

Thanks for the information.

Regards

Russ

you need to measure DC + & - direct on the 470uf 50V cap. this is for back light.. so the 12V feed the main boards are correct you can try yours main boards..

[Russ17]

Re: Toshiba 43L3753DB Screen Issue

I measured the voltages with respect to the metal chassis of the TV, which is effectively connected to 0V on the PCB (and - of C55), via the screws which secure the PSU to the chassis (I always measure voltage on the isolated side of the PSU like this).

Using this method, the 12V is correct, so I will need to establish why the 24V is so high.

I guess if one of the three diodes (D23/24/25) is faulty, it could cause an increased voltage.

A bit more testing is required.

[Diah]

Re: Toshiba 43L3753DB Screen Issue

if you think so why you still didnt test them with diode mode, but should one by one after solder out one legs.

the things i know this is Transformer ac output. only under load will read the dc voltage correct.

[budm]

Re: Toshiba 43L3753DB Screen Issue

Please provide Hi-res pictures of the whole top and bottom side of the power supply board, right now I cannot read any prints on the board.
BTW, what the P/N of the power supply PCB? 17IP???
Also upload the schematic you are using, one thing about VESTEL schematic for the power supply board, the Voltages and the component value will not match your PCBA, the schematic is the Master schematic for making Blank PCB, then the PCB will be stuffed to make many PCBA's for the needed TV model that may require difference Voltages than what being shown on the schematic, you can see that not all components are installed on your PCBA. Look at the filter cap connected to the Cathode of the D23/24/25, is that cap rated at 560uF 35VDC?

Also: https://www.badcaps.net/forum/attach...9&d=1605896639
You have bad screen if those lines stay like that and not change. Do they?

[budm]

Re: Toshiba 43L3753DB Screen Issue

OK, I now see the PCB is 17IPS62 and the PCBA is 27878395.

[Russ17]

Re: Toshiba 43L3753DB Screen Issue

Dear Budm

I am struggling to find a schematic that matches my exact PCB type. However, from what I see on the schematic, the output from D23/D24/D25 is only used to provide the LED backlight supply, so in a larger 43"screen, it is conceivable that the output on the cathode of these theee diodes would be 37V, especially as the smoothing capacitor C55 has been rated at a higher voltage (50V instead of the 35V, and a lower capacitance 470uF vs 560uF on the schematic for a 24V output).

The screen is able to give a good image under certain conditions, as stated before. All areas of the screen can give good images, but only when small areas of the screen have data sent to them. If data is sent to the entire screen (e.g. at startup when the splash screen is shown) the data is unreadable, so you get lines instead of the required image.
I will also try connecting an input to HDMI2 (this is all I can select), but I would be amazed if I get a picture.
I guess it could be an issue with the mainboard, where the video overlays are generated, which causes corruption of the data that provides those overlays.

Thanks for you support

[budm]

Re: Toshiba 43L3753DB Screen Issue

At this point I will not worry about the 37V power supply, the 37V is the feeding Voltage to the Boost converter circuit to drive the LED strings which are working at this point. That is strange white vertical block shown in your picture. Lines like that usually due to bad panel (https://www.badcaps.net/forum/attach...9&d=1605896639).
What is the history of the TV?

[Diah]

Re: Toshiba 43L3753DB Screen Issue

if bad panel . the displaying picture will remain bad over any kind of signal. its Main boards / Firmware (MFC issue)

[Russ17]

Re: Toshiba 43L3753DB Screen Issue

Hi Both

@ Diah: If I need firmware, is there a source for this on here?

I have a main board from a 32"version of the same TV, which had a smashed screen. Is it possible, without de-soldering the EEPROM, to copy the file out on to a memory stick, and then load it on to the target set?

Sorry, I am really new to Firmware issues, so need to learn quickly.

@ Budm: The TV was given to me as faulty, so I know nothing about it, and cannot find out anything from the previous owner. I would be amazed if it were a bad panel, as it can display images (generated by the mainboard) correctly sometimes.

I need to try a source on the HDMI.


Regards

Russell

[Diah]

Re: Toshiba 43L3753DB Screen Issue

at brand Vestel can all FW profiles dumped via usb and write back at same way... search after vestel service menu USB Option to dump yours original FM. and also you can reset the firmware at same menu.. who knows yours ORG. MB could be fixed too if firmware issue.

[Russ17]

Re: Toshiba 43L3753DB Screen Issue

at brand Vestel can all FW profiles dumped via usb and write back at same way... search after vestel service menu USB Option to dump yours original FM. and also you can reset the firmware at same menu.. who knows yours ORG. MB could be fixed too if firmware issue.

Diah,

Sorry if I am misunderstanding you.

Do you mean:

• Fit the other Mainboard I have to the TV
  Enter Vestel Service Menu
  Find the "Dump Firmware to "USB option in Service Menu
  Dump the FW to the USB Stick
  Fit the orginal Mainboard
  Enter Service Menu
  Load FW from USB stick
  Hope This fixes the issue

You also say it may be possible to reset the Firmware of the original Mainboard, in the Service menu.

Please correct me if I have misunderstood you instructions

Thanks for your help

[Diah]

Re: Toshiba 43L3753DB Screen Issue

Diah,

Sorry if I am misunderstanding you.

Do you mean:

• Fit the other Mainboard I have to the TV
  Enter Vestel Service Menu
  Find the "Dump Firmware to "USB option in Service Menu
  Dump the FW to the USB Stick
  Fit the orginal Mainboard
  Enter Service Menu
  Load FW from USB stick
  Hope This fixes the issue

You also say it may be possible to reset the Firmware of the original Mainboard, in the Service menu.

Please correct me if I have misunderstood you instructions

Thanks for your help

it make no sense to do any further steps if you fit the main boards you have because it will work with out any modify. !!!

on original MB you can do reset and dump

BTW: can you write yours Main boards label over here 17MB...?

Okay yours 17MB110P