Troubleshooting a Toshiba LCD TV. Model 40AV700E

[Wodger]

Hi everyone,

Short story, I was asked to look at this TV by a close friend. Originally, the TV screen would go off after a random amount of time, unplugging it from the wall for a while and then powering on again usually would bring it back to life. Here in the Philippines, power interruptions are regular. Having experienced a similar state with my LCD monitor for PC (blown caps), I had a look at the power board - 2 caps were bulged and I replaced all.

The TV apparently worked for a while (few days) then it started acting up again. On another inspection, everything looked normal.

I was called away for work for a while and on my return my friend said the TV screen finally went off and never gave a picture again (even when power cycling), so he had bought a new one and offered this broken one to me (never one to turn down a challenge).

I have no idea if the speakers were working without the screen being on.

So, situation: I have power light that changes from red to green with power button or remote, but no picture, no white screen and no obvious moving pictures with a flashlight. No signs of burn damage on the boards or loose cables.

Connecting a source to HDMI 1 doesn't show anything connected (connecting an output from a PC GPU doesn't show the TV on the OS).

I've had a read with budm's LCD TV troubleshooting guide, I don't have car lamps handy at the moment but is there anything I can do in the meantime while I get some holders and lamps?

The powerboard is a "PSIV231I01T" (picture attached).

Appreciate comments,

Regards,

Pete

[Diah]

Front LED change from red to green.with no sign of life.. this behavior Toshiba known issue... its Glitch at Firmware... flash the firmware complete.

[Wodger]

Front LED change from red to green.with no sign of life.. this behavior Toshiba known issue... its Glitch at Firmware... flash the firmware complete.

I have had a look for the firmware online - Dr-Bios offers a firmware locked behind a paywall, the toshiba sites (both) do not list this model. Google doesn't seem to have the firmware listed anywhere either.

Anyone who has a firmware dump that could provide would be appreciated.

Thanks,

Pete

[Diah]

check yours main boards... it could be vestel boards begin with 17mb

[Diah]

also this old one they used SPI/NOR Flash for firmware... easy can dump it and write it on new chips... usually by Toshiba the SPI will get no IC101 while the main cpu will be IC100
you can check the SPI if it had 3,3V ... or use the UART service port to capture the start log of the firmware.

[Wodger]

check yours main boards... it could be vestel boards begin with 17mb

Attached picture of mainboard

also this old one they used SPI/NOR Flash for firmware... easy can dump it and write it on new chips... usually by Toshiba the SPI will get no IC101 while the main cpu will be IC100
you can check the SPI if it had 3,3V ... or use the UART service port to capture the start log of the firmware.

What would be required to make an interface for capturing the log? Assuming the interface port is the 5 pin top right corner? (the 3.5mm jack by 15pin VGA connection is audio out for that PC connection)

Pete

[Diah]

this is the service manual.... check first the SPI

[Wodger]

this is the service manual.... check first the SPI

Thanks for this, it's late here (+12am), I will have a closer look tomorrow.

My background is marine engineering, so not in depth with deep electronics - but I will hunt for the SPI chip and its supply of 3.3v once other jobs are out the way tomorrow.

Pete

[Wodger]

this is the service manual.... check first the SPI

Good Day,

Using your advice about toshiba naming IC101 as SPI and the service manual you provided, I confirm 3.3v present on VCC pin 8 for SPI "IC101" in standby and on state

(I went for IC103 originally and had 3.3v on there also but then checked your manual and realized I had wrong one 😅 ).

Now for the other jobs for the day,

Pete

[Diah]

you need to check
1- T-CON fuse from both side if it had 12V
2- check with torch light if the screen have dark picture... could be the BL Lamp defect or need resoldering on power boards side .... same to check if there are sound when you feed it with HDMI signal

[Wodger]

you need to check
1- T-CON fuse from both side if it had 12V
2- check with torch light if the screen have dark picture... could be the BL Lamp defect or need resoldering on power boards side .... same to check if there are sound when you feed it with HDMI signal

1. Searched drawing and board for fuse on TCON board, couldn't spot. Attached picture showed where I tested on T-Con board input from power board - marked values - readings the same both sides of SMD's
2. Used HDMI input from Rpi playing video (started with another screen then swapped HDMI cable to TV), no sound or picture observed with flashlight.

Going by results of 1. 12V side supply to TCON from powerboard appears an issue?

Pete

[Wodger]

1. Searched drawing and board for fuse on TCON board, couldn't spot. Attached picture showed where I tested on T-Con board input from power board - marked values - readings the same both sides of SMD's
2. Used HDMI input from Rpi playing video (started with another screen then swapped HDMI cable to TV), no sound or picture observed with flashlight.

Going by results of 1. 12V side supply to TCON from powerboard appears an issue?

Pete

Following back to transformer from hot to cold - "TM802S" on power board appears no 12V output on secondary side pins

[lotas]

1. Searched drawing and board for fuse on TCON board, couldn't spot. Attached picture showed where I tested on T-Con board input from power board - marked values - readings the same both sides of SMD's
2. Used HDMI input from Rpi playing video (started with another screen then swapped HDMI cable to TV), no sound or picture observed with flashlight.

Going by results of 1. 12V side supply to TCON from powerboard appears an issue?

Pete

What are you measuring and where, you don't even know what T-CON is?
And 12V power is supplied to the t-con from the motherboard, and not from the power supply.

[nomoresonys]

That isn't his tcon, Wodger post a good clear picture of your whole tcon not just a portion of it.

[Wodger]

Gentleman,

I have 3 boards visible on this TV, 1 main powerboard (top post), what I assumed to be the TCON board but is actually the mainboard (post 6) - thats what happens when its nearly midnight and your tired. The TCON board is hidden behind a backplate at the top of the screen and I will get a picture once I get back to it later.

According to the manual supplied by Diah (post 7), 12V appears to be supplied to the mainboard from the powerboard and again due to misunderstanding, I measured on the mainboard incoming supply from power board and cut down picture is of mainboard NOT TCON (post 11).

Thanks everyone for your assistance, and I will revert later with the picture for nomoresonys

Pete

[nomoresonys]

Lol, right, I wasn't paying much attention either.

[Diah]

Lol, right, I wasn't paying much attention either.

all t-CONs design share the same principle of VCC 12V on boards... just the different whom fed this 12V. PSU or MB

[nomoresonys]

all t-CONs design share the same principle of VCC 12V on boards... just the different whom fed this 12V. PSU or MB

Indeed, good point Diah.

[Wodger]

That isn't his tcon, Wodger post a good clear picture of your whole tcon not just a portion of it.

Apologies for the delay (too many things broke over new year so got busy).

Attached is a picture of the TCON board.

Regards,

Pete

[nomoresonys]

Ok, so the fuse is white, labeled F1, what is the voltage of each side, neg probe on chassis ground.