Toshiba A665-14c

[Stevedb]

Hi everybody

I am new in this forum and repairing laptops on component level.

My laptop toshiba a665-14c with motherboard LA6062p v4.0 is total dead , no lights

I changed 2 mosfet already PQ7 and PQ8. I changed 4407A tot mosfet 4407 .On Test point 2 i have 19v but ont test point p3 i have 0,2 v. Also i measure test pooint p3 to ground(massa) abouth 78 ohms.

I remove resistor Pr45 to see it came from the battery but no result.

So i mesure all components around but i found nothing shorted.

Can somebody help me? I have no scope only multimeter. I have schedule v2.0 from motherboard but it look me the same.

Please help me to fix my laptop.
Best regards

Steve

[mielta]

Re: Toshiba A665-14c

Hi
remove Battery and than inject 19v on P3 with an lab-Powersupply
and see what happend.

[Stevedb]

Re: Toshiba A665-14c

Thanks for the reply

I can not test it, i do not have a lab -powersupply.

Best regards.

Steve

[mielta]

Re: Toshiba A665-14c

then mesure on PQ8 pin4 how is the voltage

[BlueMidnight]

Re: Toshiba A665-14c

In the future, you should measure all voltages, and narrow down what the problem could be, before replacing anything. You don't want to accidentally cause a second problem that will confuse your attempts to fix the first problem.

Most of the time, it's perfectly okay to have only a multimeter. Measuring voltages tells you a lot. You should measure everything you can, especially while you are learning. Use a PDF reader that allows you to write voltages as text on the PDF. Or print out the important page(s) and write on them with pencil/pen. Make sure you understand the different kinds of transistors and how they turn on and off. If any voltages don't make sense, try to figure out if that's a problem with the circuit or with your understanding of it.

The purpose of PQ8 is to not let AC adapter power into the board until it's the right voltage. The purpose of PQ7 is to keep current from flowing backwards out the power jack. That's because, when running on battery power, current will flow through PQ8's body diode, even though PQ8 is off.

You are measuring 19V at P2 because the body diode inside PQ7 is letting voltage through (perfectly normal). If we assume that PQ7/8 are good (since you replaced them), then they must have a high voltage on their gates (pin 4) that is keeping them turned off. We need to know why they are being told to say off.

Measure the voltage on all pins of all transistors that are part of the control circuit for PQ7/8. In other words, measure every pin of PQ10, PQ13, PQ14, PQ18, and PQ20. That's the first step. Depending on what those voltages are, you might need to measure some other things later.

[Stevedb]

Re: Toshiba A665-14c

Yes ons pin4 on pQ8 I have 19v the other components I will measure Saturday. Thanks a lot for the reply already. I ordered smaller test leads it will be easier with those.

[Stevedb]

Re: Toshiba A665-14c

Hi everybody

This are the values I measured
(PQ10 D=19V , G=0,00V , S=19V) , ( PQ13 D= 0,00V , G=13,08V , S= 0,00V) , (PQ14 D=13,08V , G=0,24V , S=0,00V) , (PQ18 D=18,73V , G=0,24V , S=0,00V) , (PQ20 D=0,24V , G=0,00V , S=0,00V)

If I must measure more, let me know then.

Thanks a lot for the help

Best regards
Steve

[BlueMidnight]

Re: Toshiba A665-14c

I'm going out now. I can be more detailed later. But you have a problem with either PACIN or ACON. They are almost at 0V, and that is what is keeping the system off.

Measure voltages all around PU1 (drawn separately in the schematic as PU1A and PU1B, but it's just different pins of the same 8-pin component).

[BlueMidnight]

Re: Toshiba A665-14c

The longer explanation...

The attached picture shows the state of all the transistors. All the voltages make sense, so none of those transistors appear to be bad right now.

- PQ7/8 are off because they have 19V on their gates
- The 19V is because PQ10 is on and PQ18 is off. Normally PQ10 should be off and PQ18 should be on, which will place ~8V on the gates of PQ7/8.
- PQ10 is on because PQ13 is on.
- PQ13 is on because PQ14 is off
- PQ14 and PQ18 are (almost completely) off because of the 0.24V on their gates.
- PQ20 is off as it should be.

That 0.24V is the cause of that whole chain of events. And it is currently unexplained.

And, just a small clarification... PQ10, PQ13, and PQ20 are BJT transistors. So, instead of Drain/Gate/Source, their pins are refereed to as Collector/Base/Emitter. Or referring to them by their pin numbers is good too.

[Stevedb]

Re: Toshiba A665-14c

Hi Bluemidnight

This are the values I measured

From PU1 (1=3,4V , 2=3,3V , 3=3,7V , 4= 0,0V , 5= 0,0V , 6=3,3V , 7=0,0V , 8=0,05V)

I would check them again and I think I made a shortcut because pQ8 = defect now. He is shorted I will replace the IC again and let you know after diner. I didn't get the small measure leads. I hope they come soon.

Are the values right?

Best regards
Steve

[Stevedb]

Re: Toshiba A665-14c

Hi Bluemidnight

This are the values I measured

From PU1 (1=3,4V , 2=3,3V , 3=3,7V , 4= 0,0V , 5= 0,0V , 6=3,3V , 7=0,0V , 8=0,05V)

I would check them again and I think I made a shortcut because pQ8 = defect now. He is shorted I will replace the IC again and let you know after diner. I didn't get the small measure leads. I hope they come soon.

Are the values right?

Best regards
Steve

[Stevedb]

Re: Toshiba A665-14c

I just replaced pq8 I got just the same problem now. The original was not defect. I also measure PQ3 1=0,00V , 2= 3,39V , 3=0,00V en PQ2. D=0,00V , G=3,39V , S=0,00V

Regards
Steve

[BlueMidnight]

Re: Toshiba A665-14c

PU1A/B are comparators. If the "+" input is higher than the "-" input, then the output is left floating (i.e. it will be equal to whatever it would have been if the comparator wasn't there). But if the "-" input is less than the "+" input, the output is pulled to ground (or whatever pin 4 equals).

Right now, it looks like ACON is low because pin 7 of PU1B is low. Please confirm that there is only 0.05V on pin 8. That would mean PU1 isn't even receiving power. If so, then measure around PQ1.

Also, I think there was a typo with PQ2 and PQ3. You wrote 3.39V for the gate of PQ2, but 0V for pin 1 of PQ3. Those are directly connected together, so I really hope they aren't at different voltages :P

[BlueMidnight]

Re: Toshiba A665-14c

I'd also like to know why pin 5 of PU1B is 0V. Maybe start at PD4 and measure voltages along that path until to get to pin 5 of PU1B.

[mielta]

Re: Toshiba A665-14c

Hi
Try an biosreset

[Stevedb]

Re: Toshiba A665-14c

Hi midnight i am back

I mesure all what you ask me

So this are values

Pu1 1=3,41V , 2=3,28V, 3=3,70V , 4=0V , 5 =0,05V , 6=3,28V, 7=0,02V, 8=18,08V
PQ2 D=0,0V , G=3,38V , S=0,0V and PQ3 1(c)=3,38V , 2(b)=0,0V, 3(e)=0,0V

I. Also measure also 18,70 V testpoint N3 after 0,05V
The resistor i measure 330 0hm so there are good the other resistor i do not find.
Do you have schedule where the componets are situated. Print layout

Best regards and hoping on you answer.

Sorry the reply was late but ver busy at work and with family. I got child with disabled child.

[Stevedb]

Re: Toshiba A665-14c

See picture of the board

[Techtiger]

Re: Toshiba A665-14c

In the future, you should measure all voltages, and narrow down what the problem could be, before replacing anything. You don't want to accidentally cause a second problem that will confuse your attempts to fix the first problem.

Most of the time, it's perfectly okay to have only a multimeter. Measuring voltages tells you a lot. You should measure everything you can, especially while you are learning. Use a PDF reader that allows you to write voltages as text on the PDF. Or print out the important page(s) and write on them with pencil/pen. Make sure you understand the different kinds of transistors and how they turn on and off. If any voltages don't make sense, try to figure out if that's a problem with the circuit or with your understanding of it.

The purpose of PQ8 is to not let AC adapter power into the board until it's the right voltage. The purpose of PQ7 is to keep current from flowing backwards out the power jack. That's because, when running on battery power, current will flow through PQ8's body diode, even though PQ8 is off.

You are measuring 19V at P2 because the body diode inside PQ7 is letting voltage through (perfectly normal). If we assume that PQ7/8 are good (since you replaced them), then they must have a high voltage on their gates (pin 4) that is keeping them turned off. We need to know why they are being told to say off.

Measure the voltage on all pins of all transistors that are part of the control circuit for PQ7/8. In other words, measure every pin of PQ10, PQ13, PQ14, PQ18, and PQ20. That's the first step. Depending on what those voltages are, you might need to measure some other things later.

BlueMidnight thanks for your Advise some important points

[BlueMidnight]

Re: Toshiba A665-14c

Alright, those voltages make much more sense. The attached picture shows the voltages as I understand them. Please do let me know if I have any typos.

So if this is right, then it looks like PU1 is operating correctly, and there is a short to ground on B+.

You should be able to confirm this by setting your multimeter to diode mode and measuring from ground to B+ (red lead on ground and black on B+). See if it measures as near zero. I would also do the same thing to check pins 8, 11, 17, and 20 of PU6 (just because shorts on the 3V/5V rails are so common).

If there is a short, you can handle it a couple different ways. You can use a bench power supply to inject a small amount of power onto B+ and then feel which component is getting warm. Or, you can make use of all the solder jumpers on the B+ rail. For example, if you remove the solder on PJ19, it will isolate that part of the board. Then check to see if the short on B+ is gone. That way you can easily narrow down where the short is.

[Stevedb]

Re: Toshiba A665-14c

Hi Midnight i measure the things you said but no short.

Black on B+ and red on massa
From testpoint N3 i got 120R
PU6 pin 8=95K , 11=740R , 17= 29,9K and 20=748R

Best regards PJ19 i do not find.