Toshiba L55-B5276 turns on, but screen is dead

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

I'm a beginner in laptop repair, usually I repair home theater receivers, TVs in the past.
The BIOS has 3.3V at pin #1.
I will have to check the EC as well, but I believe that I have there as well.
Also I have a scope as well.
Which pin should I scope, at the BIOS IC?

[emestee]

Re: Toshiba L55-B5276 turns on, but screen is dead

Find the datasheet of the IC and it will tell you. Typically pins 2 and 5 are the data pins. 20ms/div is an useful setting for the scope.

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

Bulgaria, hmm? Originally I'm from Romania.
I know that I have a Novatech EC.
I will check these, most likely tomorrow.

[emestee]

Re: Toshiba L55-B5276 turns on, but screen is dead

I'm actually from Israel, I live in Bulgaria these days.

The EC youre talking about is probably Nuvoton. I don't think Novatech is a thing. And it'll be much easier to check the data exchange on the BIOS side.

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

Most likely you are right, I don't have the board in front of me.

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

I can't find a datasheet, for Nuvoton NPCE985LA0DX.
This EC has a software in it, or it can be just purchased and replaced?
BIOS IC is a 25B64BSIG. I have to check the signal, at SI pin(Data input) pin #5?

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

I don't have a POST card(don't even know what that is), but I have a scope(Rigol).
BIOS IC at pin #1 has 3.3V.
Since I don't have a schematic for the EC, I don't know which pin should have the 3.3V.
I could start measuring around it, if there is any 3.3V present.

[emestee]

Re: Toshiba L55-B5276 turns on, but screen is dead

I don't have a POST card(don't even know what that is), but I have a scope(Rigol).
BIOS IC at pin #1 has 3.3V.
Since I don't have a schematic for the EC, I don't know which pin should have the 3.3V.
I could start measuring around it, if there is any 3.3V present.

According to russian forums, VCC is on pins 4 and 88. There is no internal firmware flash. Find a similar board schematic that has the same EC and the pre-boot signals and at least some of the GPIOs will be the same. A power on sequence/flow diagram would be excellent too.

Put the scope on one of the data pins of the BIOS chip and start the machine. If the pre-boot EC initialization is okay, it will read out the firmware from the BIOS chip and proceed to boot. You would see this on the scope.

A POST card is a device that hooks into the LPC bus and reads diagnostic codes from it as the machine initializes. You may want to get one.

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

I know now what is a post card, I have one for desktop PCs, but that most likely won't work here.
It matters at which pin I check the signal, pin #2 or #5, at the BIOS chip?

[emestee]

Re: Toshiba L55-B5276 turns on, but screen is dead

I know now what is a post card, I have one for desktop PCs, but that most likely won't work here.
It matters at which pin I check the signal, pin #2 or #5, at the BIOS chip?

You can solder the LPC pins, and it'll work.

You can check either pin, the requests on one pin should cause responses on the other.

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

Where is this LPC bus port, on a laptop board?

[emestee]

Re: Toshiba L55-B5276 turns on, but screen is dead

Where is this LPC bus port, on a laptop board?

Really depends on the board, but all ECs have them. Some boards route them to keyboard connector or mini-pcie, some have an unsoldered debug connector, Asus in particular likes to feed it to the unused RAM slot pins. If you have schematics, it's easily traceable, they're always called AD0..4 and similar.

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

Unfortunately, there are no schematics for this board.
I will look at it and, if I can't find it, I will make some pictures.

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

Ok, something got messed up, around the 1.35V and 1.05V coils just came out a smoke. It had a very bad smell.The memory stick got warm. I can't explain it what happened.
I did not see signal with the scope at the Bios chip. At pin #4 at the EC there it was 3.3V.
Two FETs, one at each 1.35V and 1.05V are shorted to ground.
For now I will take a break, unit I will have new FETs.
Thank you very much for your help, it is much appreciated.

[Papapitbull]

Re: Toshiba L55-B5276 turns on, but screen is dead

any updates on this?

[tibimakai]

Re: Toshiba L55-B5276 turns on, but screen is dead

I gave up, and got rid of it.

[Papapitbull]

Re: Toshiba L55-B5276 turns on, but screen is dead

sad