Toshiba C660 PWWAA_LA6841 hot mosfet

[sparker1]

Hello, I have this board and it won't post. I noted that PL401 was burnt away altogether. I replaced it and then noticed mosfet PQ401 got very hot. I removed it and tested it off the board and it was shorted drain/source/gate. The pads on the board were not shorted so I replaced the mosfet with another one. The board came to life briefly but then died and the same mosfet got hot and is shorted again. I now note that the 2 capacitors adjacent to PL401 also seem to be shorted. One of them is really tiny. The screen printing on the toshiba board is not comprehensive and the capacitors are not stamped with a number but I think they are PC416 and 418.
Any ideas as to what is causing so much trauma to PQ401 and PL401?

[xxxvirus1987xxx]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

are u already replace the 4466?bettert to replace that caps then touch the mosfet for a few seconds.....if the mosfet run col fixed it...or trace the ouptut of the mosfet where is goes maybe their are heavy load causing the mosfet burn again..

[c_hegge]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

PL401 is a coil, which appears to be on the output of PQ401, which is a transistor. I can't tell what the shorted capacitor is marked from the picture (it is too blurry), but if it is on PQ4's output after the coil, it will be shorting the output, which would be why the two parts are overheating and failing.

[highpulse]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

attention that a not correct coil could make this to happen as well .

[polytek]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

remove pl401, touch the mosfet if steel hot, replace all b+ 1,05 cap

[sparker1]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

OK. Thanks for all inputs. I'll do it today and get post the results.

[sparker1]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

I replaced mosfet PQ401 and capacitor PC416. Tested all pads for shorts and found none. Tried to power it and PQ401 shorted again. I removed inductor PL401 and tested pads for shorts and there was none and PQ401 does not get hot with the inductor removed. However, The voltage at one pad of PL401 and one end of capacitor PC416 is over 18 volts. I thought it was supposed to be 1.05 volts. I can't find 18.5 volts anywhere else in the vicinity of PC416 including the other caps in the area. The original inductor had been burnt away and maybe this is the reason. Is 18.5V correct? Where would this high voltage come from? I would really like some help as to where I should look now. Not all the components are labelled on the MB and I'm a bit lost with schematics, to put it mildly. Some more photo's as there was some flash glare in the first lot.

[ktmmotocross]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

its ok. b+ have 18-20V

check signal from ic to pq401. with osciloscope or with multimeter

[sparker1]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

Hi ktmmotocross, do you mean the voltages on pins 12, 13 and 14 on PU400? It will have to be with a multimeter.

[atsio]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

Replace again pq401 and also replace PQ402 and PU400

[sparker1]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

Replace again pq401 and also replace PQ402 and PU400

Ok. Post the results tomorrow.

[sparker1]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

Some progress! I replaced PQ401, PQ402 and U400 as recommended by Atsio. Now when the button is pressed the fans spin, the led lights come on and there is a brief white flash on the screen as if the bios is about to load but that is it. There is no output to an external monitor. If I switch off and then try and start it will not repeat the process. The led lights will initially come on but then the start LED will switch off. The power/battery LED remains on. However, if I disconnect the adapter and reconnect and press the start it will go through the longer loop with both LED's and fan spinning etc. Could this be a bios problem?

[atsio]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

Probably problem and on other fets. I suspect the 3v because of the led light. PQ331 and PQ332. Remove them from the circuitry and check them.

[sparker1]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

Ok. Thanks Atsio. Will post results tomorrow. I should also add that the laptop will stay on but no video output so it could be a southbridge problem? Maybe I should try a reflow if PQ331/2 are OK.

[sparker1]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

Removed PQ331/2 and tested AO4466 which was OK. I replaced PQ332 (AO4712) because I couldn't test it with my knowledge and the schotky diode it has. Anyway, I must have stuffed something else up because now no lights come on and PQ331 gets very hot. Might replace PU330. I'll have another look at what it could be tomorrow but a friend says he might have a spare MB for one of these and if he comes through I'll bin this one.

[sparker1]

Re: Toshiba C660 PWWAA_LA6841 hot mosfet

Saga continues. Mates board worse than mine but a good source for parts. Anyway, now I have no power light at all. PQ204 (AO4407A) keeps blowing and on removal all drain pads on MB are shorted. Where would I look next? I have replaced PQ203, PR215, and PC211 and there was no change.