Toshiba l300 no power

[shuky]

hello
i have toshiba L300 with no power no led working and no charging ...
all fuse is ok.
can u tell me what to check and how or replace from a photo ?

thank you

[damaniauk]

Re: Toshiba l300 no power

hello

[azry]

Re: Toshiba l300 no power

check for the any short cap first...

[unlockdev]

Re: Toshiba l300 no power

check the ao mosfet

[juus]

Re: Toshiba l300 no power

hi, new here and have same problem. Can you say which caps to check from pics? And where is mosfet located?
I have checked power adapter - works & gets 19v on board at connector. But laptop L300 will not power up or charge. Only battery light will flash 6 times when power button pressed. Any help will be appreciatted.
Thanks

[momaka]

Re: Toshiba l300 no power

Start by posting good quality pictures. Need 1 picture that shows the whole motherboard, and at least 1 of the area near the power jack. Without pictures, it's hard to say what to test exactly.

Use the forum's "Manage Attachments" feature to attach your pictures rather than an off-site host.

[juus]

Re: Toshiba l300 no power

ok i will disassemble & take pics, although it looks same as the first post.

[juus]

Re: Toshiba l300 no power

here are pics of board top and bottom and area where power is at. Any help would be appreciated.

[juus]

Re: Toshiba l300 no power

anyone able to help?

[momaka]

Re: Toshiba l300 no power

anyone able to help?

Using the second picture you posted as a reference...

Check the fuses first - i.e. FUSE500 and FUSE501. They should show continuity/very low resistance with a multimeter.
Also check inductor L500 - again, you should see a very low resistance across.

Other things to check are the MOSFETs - Q500, Q502, Q506, and Q507.
- Measuring resistance between left side and right side of Q500 should NOT show short circuit or low resistance. Additionally, neither the left side nor the right side of Q500 should have low resistance to ground.
- Measuring resistance between top and bottom side of Q502, Q506, and Q507 should NOT show short circuit/low resistance. Among all of these MOSFETs, only Q506 should have zero/low resistance to ground on it's lower 3 pins that are connected together.

Check diodes D500, D502, and D508. None of them should show short circuit/ very low resistance in any direction.

Also check all of the small ceramic capacitors for short circuits across.

R502 looks slightly burned. I can't tell very well, but it looks like it has "100" written on top. If so, that would be a 10 Ohm resistor - make sure it shows 10 Ohms or less resistance (less because it might be in parallel with other components). If it's higher than 5% of it's stated value, it's bad.

Lastly, what are the part numbers on U502?
...
Post you finding here or let me know if you have any other questions.

[juus]

Re: Toshiba l300 no power

Ok so followed instruction:

U502 part #: BQ 24721C TI 83K DTHX G4

FUSE500 & 501 - show no resistance / continuity (LF 15A + LF 8A written on top of fuses)
L500 - shows no resistance / continuity
Q500, 502, 506, 507 - all measure OK
D500 shows no resistance / continuity
R502 measures ok, cannot make out writing looks like 100.

Strange previously fuses showed continuity but i must have done something wrong as i double checked everything again and above are the results.
So from what i see i need to replace the fuses, L500 & D500.
Will await your valued input.

[momaka]

Re: Toshiba l300 no power

FUSE500 & 501 - show no resistance / continuity (LF 15A + LF 8A written on top of fuses)
L500 - shows no resistance / continuity
D500 shows no resistance / continuity

Check you readings on those again. Diodes almost always fail short-circuit, not open circuit. You'll either see a short circuit/very low resistance (usually less than 20 ohms) regardless of which way you orient the multimeter probes (this would indicated a bad diode), or you will a reading one way but not the other (good diode reading out of circuit).

One thing that comes to mind here is leftover flux on the joints. When measuring components, scratch the leads on each component a little bit with your multimeter probes - this will remove any surface flux that may block your probes from touching the metal contacts on the component.
Also, when you turn on your multimeter, first touch both probes together to make sure your multimeter reads 0 resistance/continuity. Then proceed to checking the components.
On most digital multimeters, continuity check is also diode test. If this isn't the case on yours, use the diode test function when checking the diodes.

Q500, 502, 506, 507 - all measure OK
...
R502 measures ok, cannot make out writing looks like 100.

What values did you get?

U502 part #: BQ 24721C TI 83K DTHX G4

Perfect.
I think this is the data sheet for it:
https://cdn.badcaps-static.com/pdfs/...35349d920c.pdf
The first few pages give information about the pins. Also, page 21 to 23 have sample circuits that may be close to what you have on your board. Should be helpful later on after all bad components have been checked/replaced.

At this point, I think you should first (re)-check some of the components I mentioned above as well as all of the ceramic capacitors in that area for short circuits. Any readings under 20 Ohms for a ceramic capacitor should be considered suspicious. Let me know if you find any.

[fabiog]

Re: Toshiba l300 no power

When I try to measure continuity on 330uf tantulum 2.5v capacitors on my laptop ,the multimeter beeps and show 0 on a few but with most it shows a one.
does this mean some are defective?
They are similar to the black ones in this picture:
http://www.diytrade.com/china/4/prod...2R5ATE015.html

[Th3_uN1Qu3]

Re: Toshiba l300 no power

The CPU or chipset can distort those readings. If it's a cap in the CPU area, remove the CPU and test again. If it's near the chipset... it's a matter of luck.

[fabiog]

Re: Toshiba l300 no power

Is continuity supposed to be 0 (beep) or 1?

[momaka]

Re: Toshiba l300 no power

Is continuity supposed to be 0 (beep) or 1?

Depends on where the 1 is located. On some multimeters, an open circuit will appear as "1" on the left side of the screen. On others, it might be 0L.
In any case, if you get a 0 (or close, like less than 1 Ohm) with a beep, then that means you have a short circuit.

[fabiog]

Re: Toshiba l300 no power

Excuse by basic question but is a short circuit a bad thing? ,should I be testing the capacitors with the laptop charger plugged in or not?
If the capacitors show 0 on the meter are those bad?

Thanks for the help so far.

[juus]

Re: Toshiba l300 no power

Hey there momaka, sorry have been away on work project.
Will get you those results & post in the morning.

[momaka]

Re: Toshiba l300 no power

Excuse by basic question but is a short circuit a bad thing?

Depends on the component your measuring.
- If it's a fuse, for example, a short circuit (or zero resistance) across would be a good thing.
- If it's a capacitor and you're measuring it outside of the circuit (i.e. removed from the board), then it's not a good thing. If the capacitor is in circuit, however, a short circuit does not necessarily mean the capacitor is bad. This is because in circuit you can have other components in parallel with the capacitor that may read low resistance.

should I be testing the capacitors with the laptop charger plugged in or not?

No, never measure resistance or continuity with the power plugged in.

If the capacitors show 0 on the meter are those bad?

Not necessarily, as I stated above. Depends on where in the circuit the capacitor is measuring. If you remove the capacitor and it still shows 0 ohms, though, then it is bad.

[juus]

Re: Toshiba l300 no power

Hi momaka

Here are readings i get with components
Fuses 500/501 = 0
Q500 - 830 / Q502 - 540 / Q506 - 420 / Q507 - 165 (strange is 3 legs across will measure same then last 1 across is higher than 1st 3 reading on all 4 chips) hope u understood that
D500 -148 / D502 - 770 / D508 - 1328 & when reverse multimeter cables on D508 get 165 reading, on all others no reading when reverse cables.

Check all other small components all fine. At least according to me.
Hope you can figure out what ive posted

U502 i dont know how to test
Still a noob here learning