Toshiba L300 - no boot - not NEC Tokin

[spleenharvester]

Hey all. Acquired an L300D-146 with the hope it just needed the standard NEC Tokin fix. It doesn't have the capacitor yet exhibits similar symptoms. Boots, all LEDs, fan powers, no display and has to be disconnected at the power supply.

It seems a very similar circumstance to the HP 6735s 5 caps error, especially given it's an Inventec board of very similar design. There is a strong burnt smell in the U16-U17 region - which supply the 3.3v rail - but all voltages tested at pads are very much present. Interesting thing - a similar part failed on one of the 6735s, which someone I sold the faulty board to replaced and got working again.

Any ideas? It's this one:

Nothing seems to be getting boiling hot, and all CPU/GPU/SB are getting warm so evidently receiving power.

[Francisco.s]

Re: Toshiba L300 - no boot - not NEC Tokin

U16-U17 region - which supply the 3.3v rail

Can't find U16-U17 in the supply circuit of the 3.3v rail. Do you have the right schematic?

[spleenharvester]

Re: Toshiba L300 - no boot - not NEC Tokin

It's parts U16 and U17 mate, they're in the same area. Sorry for the wording :p

I think I'll check the V3A, V3S etc rails. Is it best to check at every single point at which they come up in the schematic?

I have 3 6735s boards with the 5 caps issue, and now this one Toshiba board which is startlingly similar in design. It would be great if I could get to the bottom of this.

Someone in a 6735s thread had a theory that there was a power problem with the KBC-1091 chip. It's frustrating as hell because all voltages are there at the test points, all components heat up etc, but nothing

EDIT: The U16 and U17 are close to the small BQ qfn IC (I'll get the model number later) - the same one near to which the faulty component was found on the 6735s. I think I may be on to something.

I'll get pics up soon too.

[spleenharvester]

Re: Toshiba L300 - no boot - not NEC Tokin

I think I may have found it. C191, 0.1uF 16v ceramic cap, visibly a bit blackened. Appears to be working on the DMM - 3.3v on one side and 0v on the ground side. Resistance test in either direction is fine too.

Very strong smell coming from this area (a bit like really, really bad BO?) so going to replace it and report back.



I'll try get a photo when I can access a decent camera, the ones we have in the house at the moment are tragic.

Reckon C191 being faulty could cause this? Another area with the BO smell is U6.

[spleenharvester]

Re: Toshiba L300 - no boot - not NEC Tokin

Starting to suspect the Winbond WPCE775 chip may be at fault, or something powering it. It warms up though.

Is it worth replacing it since I have a spare anyway? Do these kinds of things fail?

Some odd voltages around the BIOS chip, I have yet to confirm.

[spleenharvester]

Re: Toshiba L300 - no boot - not NEC Tokin

Just found this video http://www.youtube.com/watch?v=66s-SVqcstI a very similar controller, WPCE773, was faulty. Very similar indeed. Gonna replace and report back - might help somebody else.

[spidey]

Re: Toshiba L300 - no boot - not NEC Tokin

i dont believe that video. that is the power ic (aka keyboard controller ic) and if it is burnt, system doesnt power up. At least i didnt see such an issue.

[spleenharvester]

Re: Toshiba L300 - no boot - not NEC Tokin

Took a few more readings and it pointed towards the WPC775 chip being dead even more. Tried to replace it and it lifted some pads with it. :/

I really need to buy a decent soldering station, I've wasted one too many repairable motherboards this way.

[spidey]

Re: Toshiba L300 - no boot - not NEC Tokin

use some green wires and check from the schematic.

[spleenharvester]

Re: Toshiba L300 - no boot - not NEC Tokin

Nah this one's a gonner matey, there's about 12 pads lifted out.

I'd like to get hold of another identical board at some point (or a 6735s board that I haven't damaged while taking readings) and try again though. I think I'm on to something here with the KBC controller.

[jfnzihou]

Re: Toshiba L300 - no boot - not NEC Tokin

I have two Toshiba L300 motherboards. These starded to freeze windows and nod could no loguer boot (these still power, but no video output).
I have removed the NecTokin capacitors and replaced with tantalum (3 x 330uF), but still no video.
Any idea?

[spleenharvester]

Re: Toshiba L300 - no boot - not NEC Tokin

You need 4x330uF I think matey, I may be wrong though. Which caps did you use? What voltage/ESR? Did you put them in the right way, outside positive?

Did you remove the Tokin with a heatgun or pull it off in pieces?

If it was a Tokin board chances are it's just the wrong caps, they almost never seem to fail in any other way.

Get your Multimeter and set it to the 200ohm setting, and check the resistance across each of the capacitors. You'll see pretty easily if there's a short - that would cause the problem you are experiencing. (It's pretty easy to bridge across the two sides without realising)