Toshiba a300-20w strange voltage

[rippergr]

Hello,
I have a strange problem with a toshiba a300-20w. When I check voltage in dc jack the reading is 2.5V
I changed the dc adaptor and still the same reading. If I remove the jack from the motherboard and check the reading in the dc jack pins the voltage is 19,5V.
I suppose I have short circuit in acomponent but I can't find it.
I found a short capacitor(picture 1) but when I remove it and measure the to ends where the capacitor was on board it still shows short.
I cant find a decent schematics.
If someone can help me.

[atsio]

Re: Toshiba a300-20w strange voltage

For schematic look at this post
https://www.badcaps.net/forum/showthread.php?t=42747

[fddizon]

Re: Toshiba a300-20w strange voltage

if you can and have the skill, remove U803 and retest capacitor on board. more likely BQ chip is shorted

[rippergr]

Re: Toshiba a300-20w strange voltage

I removed U803 the capacitor seems still shorted and the voltage is still 2.5V even in dc adaptor

[atsio]

Re: Toshiba a300-20w strange voltage

You are looking at the wrong place. Just check what is getting hot when you plug in the dc adaptor.

[rippergr]

Re: Toshiba a300-20w strange voltage

I already check that but nothiung seems to get hot and I am pretty sure that the problem is very close to dc jack becuase without U803 the problem persists.

[atsio]

Re: Toshiba a300-20w strange voltage

I already check that but nothiung seems to get hot and I am pretty sure that the problem is very close to dc jack becuase without U803 the problem persists.

That is what I am saying. If the problem is a capacitor probably you will not find it by hand. You need to use a thermocouple. Check resistance relative to ground on pins of Q801 to determine which side of rail is shorted.

[rippergr]

Re: Toshiba a300-20w strange voltage

on mosfet Q801 5,6,7,8 pins are short to ground. Is that normal?

[atsio]

Re: Toshiba a300-20w strange voltage

No. You need to remove Q801, check again those pins, and if they are still shorted, then you need to connect a wire to those pins and apply voltage with a lab power supply. Start at 1v 0,2amp and increase amps-voltage until you find what is getting hot.

[rippergr]

Re: Toshiba a300-20w strange voltage

I removed Q801 but I still have 2,5 V

[atsio]

Re: Toshiba a300-20w strange voltage

What is the resistance on all the pins after removing Q801

[rippergr]

Re: Toshiba a300-20w strange voltage

I set multimeter to 2K resistance
red pin 1,2,3&4 - black 5 = no reading(1.)
red pin 1,2,3&4 - black 6 = no reading(1.)
red pin 1,2,3&4 - black 7 = no reading(1.)
red pin 1,2,3&4 - black 8 = no reading(1.)

black pin 1 - red 5,6,7 & 8 =0.500
black pin 2 - red 5,6,7 & 8 =0.500
black pin 3 - red 5,6,7 & 8 =0.500
black pin 4 - red 5,6,7 & 8 = no reading (1.)

[atsio]

Re: Toshiba a300-20w strange voltage

Resistance relative to ground

[rippergr]

Re: Toshiba a300-20w strange voltage

none of the pins is short to ground

[atsio]

Re: Toshiba a300-20w strange voltage

And with Q801 removed, do you still have 2.5v on CN801?

[rippergr]

Re: Toshiba a300-20w strange voltage

yes, exactly. I have 2,5V even in fuse801 and in dc jack

[rippergr]

Re: Toshiba a300-20w strange voltage

If I remove d801 then I have 19V in dc jack, so I am sure its not the dc adaptor.
Also if I remove the d3 I also have 19V in some points but if I measure the diodes are ok.
I assume that I have normal power because it's crucial components and near the dc jack

[dj_ricoh]

Re: Toshiba a300-20w strange voltage

lift the diode d801 up and inject voltage with a lab PSU.
normal adapter drops voltage to protect it self.

with lab psu you increase the voltage (cheap psu) until the amps go up to.

at one point you will feels something hot or smell something or if your lucky burn

i never test it but i wanna try with a table battery 3.7v with 3000(over)mAh

[rippergr]

Re: Toshiba a300-20w strange voltage

I don't have lab psu yet. I bought one from ebay but never came.
Can I test it with some other way?

[atsio]

Re: Toshiba a300-20w strange voltage

none of the pins is short to ground

What is the ohm reading?