Toshiba laptop C855 no power dead

[shelby5041]

hi

seems this is very common issue with this laptop model

100% dead.. when plugged in no lights come one front at all and wont power on

i do get 19v input and fuses check good near the power cable

motherboard part # 1310A2541801 6050A2541801

it seems it is a common part failure but i need help locating which part?

mosfet?

laptops are dime a dozen nowadays and have little to no value but if i can repair this cheap ill do it...i can buy a good used board for about $50 but thats way too much to spend on a used laptop....

tried to post some pics ..im working outside since its nice out and the sun shade creating issue

[shelby5041]

Re: Toshiba laptop C855 no power dead

any help would be greatly appreciated

[raajkumar]

Re: Toshiba laptop C855 no power dead

Start your diagnosing from mosfet.

[shelby5041]

Re: Toshiba laptop C855 no power dead

hi

can you point out in photos which mosfets?

[mcplslg123]

Re: Toshiba laptop C855 no power dead

Dear shelby. look for some shorted cap or mosfet in vcc area-just near heatsink pipe. thats the area where fault occurs in this mb most of the times. I came across fault in that area atleast 3 times in this mb in last six months. Your pic#3 to look for.

[shelby5041]

Re: Toshiba laptop C855 no power dead

Thank you

From what ive seen on youtube it seems the common issue is with mosfet near the power cable to motherboard but my board is intel chip not amd so mine doesnt have same components

How do i check for shorted mosfet in circuit and do i do it with power plugged in or no?

[shelby5041]

Re: Toshiba laptop C855 no power dead

On ebay there are many of these boards for parts repair..non working so it should be fixable since its a common issue im sure and you even backed that up

[mcplslg123]

Re: Toshiba laptop C855 no power dead

Thank you

From what ive seen on youtube it seems the common issue is with mosfet near the power cable to motherboard but my board is intel chip not amd so mine doesnt have same components

How do i check for shorted mosfet in circuit and do i do it with power plugged in or no?

You need to measure mosfet without power connected to the mb. You can measure them with multieter in diode mode. Put black probe on pin1 nad red on pin4 and measure the ratings. It should not be in continuity or too low readings. Similarly, you can measure by putting black probe on pin1 and red on pin5 and observe the ratings. If you find the ratings too low or suspicious, you should check the mosfet out of circuit by removing it from mb.

[shelby5041]

Re: Toshiba laptop C855 no power dead

Thanks ill try when i get time

One note

Other day i was probing board and with plugged in i get 19v at input and then there are two mosfets near input area and near 2 fuses....u can see in pic...

When i probed these mosfets...the one closest input power tested 19v at all 4 pins on one side...other 4 pins were 0v

The mosfet next to it tested 0v on all 8 pins

Not sure if this means anything at all

[mcplslg123]

Re: Toshiba laptop C855 no power dead

probably 19v rail shorted. Mosfet or caps is bad.

[shelby5041]

Re: Toshiba laptop C855 no power dead

thanks

so shouls i test the mosfet that has 0v on all pins or the mosfet that has 19v only on 4 pins and 0v on other pins

are both suspect ?

[shelby5041]

Re: Toshiba laptop C855 no power dead

here is a data sheet for the 2 mosfets near power input

apparently you asked me to test pins source to drain and pins source to gate..correct?

[shelby5041]

Re: Toshiba laptop C855 no power dead

should source pin be 19V power plugged in?

if not, when plugged in what if any voltage values should i see at S G and D pins?

[shelby5041]

Re: Toshiba laptop C855 no power dead

hi i did some testing..

with no power plugged in

i tested both mosfets near power input

D-S ..no continuity= ok
i then charged up drain and then D-S now has continuity= ok

so it seems those two mosfets are functioning ok

[shelby5041]

Re: Toshiba laptop C855 no power dead

if i cant find a solution soon ill prob just toss board in trash as like i said laptops are dime a dozen and doesnt make sense spening much time or effort repairing if not a quick cheap repair....

[shelby5041]

Re: Toshiba laptop C855 no power dead

hi

i may have found a suspect part..there is a mosfet alone north of the 2 mosfets and north of the power input that is near a fuse.and just southeast of the battery charging port .i just tested it and with power unplugged when i test S-D i get a 500 reading using diode....this should be no reading correct / no continuity correct??

mosfet part is TPCA 8065-H

[shelby5041]

Re: Toshiba laptop C855 no power dead

see photo

maybe im getting somewhere?

[BlueMidnight]

Re: Toshiba laptop C855 no power dead

Let's take a step back. You need to follow the power sequence in a systematic manner to determine at which point it is having trouble.

First, measure the voltage at R6000. This will tell us if power is being allowed through the input MOSFETs. If you get 19V there, then measure the voltages on L6100 and L6150 (these are for the 3.3V and 5V rails). However, if you do not get 19V at R6000, then instead measure all 5 MOSFETs in that area (indicated on the attached picture). You only need 3 measurements per FET because some pins are tied together (pins 1-3, pin 4, and pins 5-8). And also measure all pins of U6000 (located in the same area, but on the back side of the board).

The schematic is attached. U6000 and the surrounding circuitry is located on page 5.

[shelby5041]

Re: Toshiba laptop C855 no power dead

thanks bluemidnight.....ill review when i get a chance

reason i am targeting mosfets is that this is an extremely common issue with this model laptop....there are many main boards on ebay for sale that are non working due to no power

many youtube videos show bad mosfet but my version board is not exact same as videos i saw...

i appreciate your input....it should help a lot in order for me to find root cause of dead laptop......

[shelby5041]

Re: Toshiba laptop C855 no power dead

q6012 is the mosfet that i think is supect during testing in circuit via diode ....testing S-D in which i was told should be open circuit but its not testing open....but maybe since its in circuit it could be giving inaccurate results

i get a reading of 550 in diode mode when testing S-D on Q6012 and switch probes i get same reading