Toshiba A300-211 completely dead no lights at all

[Andreasbest]

Hello.
I have a A300-211 here that suddenly died, no lights, no power on via battery or charger.
Q802 and Q803 have no output..
Any advices welcomed

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

Switch and U801 miss +V5S and now searching for +V5A that i also miss.
U23 has the below voltages
Pin3 2v
Pin3 3.3v
Pin6 1.5v
Pin8 3.3v
Pin9 4.5v
Pin13 1.2v
Pin14 2v
Pin16 19v
Pin17 5v
Pin22 4.5v
all others 0v.

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

None??

[rievax_60]

Re: Toshiba A300-211 completely dead no lights at all

R809 and R810 supply a small current to the +VBAT rail. +VBAT must rise by a few volts to allow pin 5 ACDET to go high. If there is a short or too much leakage current from +VBAT to GND, U803 will not drive Q801.

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

I don't know if i understand correctly but R809 and R810 have 19v in both pins and also none is shorted to ground.

[rievax_60]

Re: Toshiba A300-211 completely dead no lights at all

I don't know if i understand correctly but R809 and R810 have 19v in both pins and also none is shorted to ground.

My mistake, I misread. Have you tried measuring +5v while turning on the computer to see if the rail it trying to come up briefly?

[rievax_60]

Re: Toshiba A300-211 completely dead no lights at all

I had a look at the data PDF for U23, TPS51125. Pins 1 and 6 are for enabling +V5A and +V3LA. Pulling to ground disables an output.
You measure 1.5v on pin 6, +3VLA should be up. What is pin 1?

[BlueMidnight]

Re: Toshiba A300-211 completely dead no lights at all

Usually, all the outputs of the 3V/5V are turned on at the same time, but this one works a little differently.

Here's what is supposed to happen:
1. ENTRIP2 goes high
2. The 3V switching output turns on
3. The EC/KBC/SIO gets 3V power, turns on, and sets EC_PW_ON high
4. ENTRIP1 goes high
5. The 5V switching output turns on

We know that:
- Your 3V/5V linear outputs are on (VREG3/VREG5).
- Your 3V/5V switching outputs are not on.
- Since ENTRIP2 is high, the 3V switching output should be on, but it isn't.
- The 5V rail won't turn on until the 3V rail is on

At first glance, it seems like we just need to check the 3V output, but U23 will shut off both outputs if there is a problem with either one. So, we need to check both.

From here it is the same troubleshooting procedure you have done before:
1. Check for shorts on the 3V and 5V outputs (easiest places to check are at the inductors L24/L20). You can also remove the solder jumpers PAD11/PAD8 to isolate the outputs and confirm the problem is located in/around U23.
2. If there are no shorts, and removing the solder jumpers doesn't help, then remove and check the MOSFETs.
3. If the MOSFETs are okay, then U23 is likely bad.

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

I had a look at the data PDF for U23, TPS51125. Pins 1 and 6 are for enabling +V5A and +V3LA. Pulling to ground disables an output.
You measure 1.5v on pin 6, +3VLA should be up. What is pin 1?

Pin 1 is 0v and no i haven't found +5v anywhere, not even in the ON/OFF switch.

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

Usually, all the outputs of the 3V/5V are turned on at the same time, but this one works a little differently.

Here's what is supposed to happen:
1. ENTRIP2 goes high
2. The 3V switching output turns on
3. The EC/KBC/SIO gets 3V power, turns on, and sets EC_PW_ON high
4. ENTRIP1 goes high
5. The 5V switching output turns on

We know that:
- Your 3V/5V linear outputs are on (VREG3/VREG5).
- Your 3V/5V switching outputs are not on.
- Since ENTRIP2 is high, the 3V switching output should be on, but it isn't.
- The 5V rail won't turn on until the 3V rail is on

At first glance, it seems like we just need to check the 3V output, but U23 will shut off both outputs if there is a problem with either one. So, we need to check both.

From here it is the same troubleshooting procedure you have done before:
1. Check for shorts on the 3V and 5V outputs (easiest places to check are at the inductors L24/L20). You can also remove the solder jumpers PAD11/PAD8 to isolate the outputs and confirm the problem is located in/around U23.
2. If there are no shorts, and removing the solder jumpers doesn't help, then remove and check the MOSFETs.
3. If the MOSFETs are okay, then U23 is likely bad.

No shorts to the ground on L24/L20 with jumpers removed but i have a intersting clue.
With jumper PAD11 removed i get 3.3v at L24 and power on Q41 and Q39, still nothing on L20.
With jumper PAD11 soldered i get 0v.
Propably a short circuit around there?
With jumper

[BlueMidnight]

Re: Toshiba A300-211 completely dead no lights at all

Okay, that is helpful.

On this particular board, the 5V won't turn on when PAD11 is removed, so that's expected. Now that we know the 3V output is working with PAD11 removed, we need to know if a problem with the 5V output is causing both outputs to shut off.

I'm not clear about what tests you did with PAD8. But if you haven't already, try this: Test the voltages at L20/24 with PAD8 connected. Test them again with PAD8 not connected. Leave PAD11 connected for both tests.

If the 3V output doesn't work no matter if PAD8 is present or not, then there is probably a short on the 3V rail. Some parts of the 3V rail are disconnected until it detects the 3V, so it's possible to have a short that you can't read at L24. The first place I would look for such a short is at pin 1 of Q36 (or wherever is most convenient to test "+V3A").

If, however, the 3V and 5V outputs work when PAD11 is connected and PAD8 is disconnected, then the short may be on the 5V rail instead.

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

My fault, with PAD8 soldered or not i get 0v on L20/L24, PAD11 always soldered.
Got a little confused with the part writings on the board, 99% sure this is the Q36 that i marked to the picture, has nothing written on it.
So in this i measure Pin1-2 0v , Pin3 5v, Pin4 0.8v (with PAD11 removed) / Pin 4 0v (with PAD11 soldered) and Pin5-6 0v.
The readings are the same with PAD8 soldered or not.

[BlueMidnight]

Re: Toshiba A300-211 completely dead no lights at all

Yes, that does sound correct for Q36. The problem must be on the 3V rail.

With power disconnected, check for a short from pin 1 to ground (diode mode, black probe on pin 1 and red probe on ground). For this test it doesn't matter if PAD8/PAD11 are connected or not.

If you find a short there, then the problem must be on that rail. If you don't find a short, then you can still do one more test to make absolutely sure...

Q36 acts as a load switch and lets the 3V pass from "+3VLA" to "+3VA". You can actually remove Q36 and test with PAD11 connected and PAD8 disconnected. This prevents the 3V from getting to "+3VA". So, if the 3V and 5V outputs both work, then you know the problem must be somewhere on "+3VA". If the outputs do not work, then the problem must be on "+3VLA"

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

No shortcircuit on Pin1 with ground.
Removed Q36, PAD11 connected, PAD8 removed, 5v are still there (pin3) but 3v still aren't (pin4 0v not 0.8v like before) both L24 and L20 have no voltage at all.

[BlueMidnight]

Re: Toshiba A300-211 completely dead no lights at all

I found a couple more load switches in the schematic. Check pin 1 on both Q40 and Q40 for shorts to ground.

We can also try to force the 5V to stay off just to make sure it's not causing a problem that is shutting off both outputs. It's easy to do this by removing Q34. Leave PAD11 connected and see if the 3V rail works. If the 3V rail works like that, then there may be something wrong with the 5V MOSFETs or even possibly U23.

If you don't find anything useful doing those steps, then the easiest thing might be to use a bench power supply (I forget if you have one or not) to inject 3V, slowly raising the current up to 1A max, on the "+V3LA" rail and see if it gets hot somewhere. "+V3LA" goes to a looooot of places.

[rievax_60]

Re: Toshiba A300-211 completely dead no lights at all

It would be good to confirm that +V3LA is trying to come up. I have seen rails come up for just a few milliseconds before shutting down due to overload, voltage overshoot or excessive ripple. This can only be checked properly with a DSO. A DMM with Peak Hold function might give some indication.
I have also seen this sort buck regulator refuse to turn on because it sensed a residual voltage already applied to the output from elsewhere.

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

I found a couple more load switches in the schematic. Check pin 1 on both Q40 and Q40 for shorts to ground.

We can also try to force the 5V to stay off just to make sure it's not causing a problem that is shutting off both outputs. It's easy to do this by removing Q34. Leave PAD11 connected and see if the 3V rail works. If the 3V rail works like that, then there may be something wrong with the 5V MOSFETs or even possibly U23.

If you don't find anything useful doing those steps, then the easiest thing might be to use a bench power supply (I forget if you have one or not) to inject 3V, slowly raising the current up to 1A max, on the "+V3LA" rail and see if it gets hot somewhere. "+V3LA" goes to a looooot of places.

Q40 and Q42 (propably this is what you meant) have no shorts to the ground.
I remove the Q34 and 3v appeared as they should to L24. That's a useful clue.

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

It would be good to confirm that +V3LA is trying to come up. I have seen rails come up for just a few milliseconds before shutting down due to overload, voltage overshoot or excessive ripple. This can only be checked properly with a DSO. A DMM with Peak Hold function might give some indication.
I have also seen this sort buck regulator refuse to turn on because it sensed a residual voltage already applied to the output from elsewhere.

Correct, when i connect the adapter on mains i get 3V at Pin4 on Q36 for about 1 second, then drops to 0v.

[BlueMidnight]

Re: Toshiba A300-211 completely dead no lights at all

Oh yes, Q42 is what I meant to type.

Well that is a very interesting result. There may be something wrong with the 5V rail after all. And because you have tried it with PAD8 disconnected, we know the problem must be close to U23.

It couldn't hurt to check the resistance of the feedback resistors R276 and R277. But the most likely cause is a problem one of the MOSFETs Q29/Q32. For example, it might be that Q32 isn't turning on. That would trip the low voltage protection and turn off both the 3V and 5V outputs.

Hopefully you remember the steps to test them. They are both N-Channel MOSFETs.

[Andreasbest]

Re: Toshiba A300-211 completely dead no lights at all

Ok i followed exactly these steps in this order and i got :
1) Red on Drain, Black on Gate (No connection. This also turns the MOSFET OFF)
2) Red on Drain, Black on Source (No connection)
3) Swap the probe positions. Red on Source, Black on Drain (One diode drop, approximately 0.5V) (Q29 0.133v, Q32 0.5v)

4) Red on Gate, Black on Drain (No connection. This also turns the MOSFET ON)
5) Red on Source, Black on Drain (Less than 0.2V) (both Q29 & Q32 gives 0000v like shortcircuit)
6) Swap the probe positions. Red on Drain, Black on Source (Less than 0.2V) (both Q29 & Q32 gives 0000v like shortcitcuit))
Haven't found the resistors yet to measure them.