Toshiba A665 blown MOSFET

[Rolin]

Re: Toshiba A665 blown MOSFET

Q29 Power ON

PIN1-3 (3.3V), PIN4 (16V), PIN5-8 (3.36V)

I can't find R410. Any ideas how to find it?

I think I understand what you're going for here. I noticed PIN4 on each Q29, Q31, and Q30 are all off the VSB. And when powered on Q29 and Q31 are both over 14V, but Q30 is only 3.13V. So our problem is somewhere along the VSB going to PIN4 on Q30? Am I catching on, or still a lot to learn!

[Rolin]

Re: Toshiba A665 blown MOSFET

"So you need to lift Q11A PIN6 to see if Q30 will be fully on just like Q31, Q30 PIN 4 should also has about 14vdc on it."

You edited your post - I'll remove the Q11 chip completely if that's OK. Let me know before I do it - seems easier to remove with my hot air station than trying to lift one leg. Let me know if it's OK...

[Duncanbest]

Re: Toshiba A665 blown MOSFET

check the resistor values of PR12 PR14 PR16 on page 34.
Maybe one of them is NG

[budm]

Re: Toshiba A665 blown MOSFET

Post 41, yes you are correct, I believe Q11A is bad, when it is supposed to be off, it still has low leakage resistance between Source and Drain (pin6, Q11A) which loads down the PIN4 Gate voltage of Q30 not allowing Q30 to be fully on, so if we can disconnect pin6 of Q11A from the circuit, Q30 then will be fully on and puts out 5V instead of 3V.
Do not remove Q11 completely since Q11B is used to put 470 Ohms load on the +5VS as you can see on page 34.

[Rolin]

Re: Toshiba A665 blown MOSFET

Lifting the pin6 on a small chip like this is very difficult (it's really very very small!) - I bent the pin to the side trying, so I had to remove the chip. I'll straighten the PIN6 out of the way and replace the chip. I'll report back when the chip is back on the board and tested with PIN 6 lifted...

[budm]

Re: Toshiba A665 blown MOSFET

I use EXACTO knife to slide under the pin while applying the heat to the pin if you have room to do it.
I have a feeling that Q11 will have to be replaced.

[Rolin]

Re: Toshiba A665 blown MOSFET

Your feelings are correct! I now have 19V on Pin4. and the fan spun up properly. I don't have everything connected so i don't know if it would POST or not, but it sounded correct.

So it's Q11. It was dragging down the VSB from PIN 6 to PIN4 of Q30. This is pretty much the last point to PIN4 Q30, so there isn't anything else that could cause this, correct?

I guess I need to find one. Is this a common chip I could find on a scrap board? There aren't many markings on the chip - i think is says K27 or something like that.

[budm]

Re: Toshiba A665 blown MOSFET

That is it, you found the problem, thanks to b700029 for pointing that out in the earlier post. Now just need to find this Dual MOSFET. Have to look at the service manual, it may be listed in the BOM.
It is getting late for me now, time for bed, cheers!
OK it is 2N7000 series, P/N 2N7002DW with CASE STYLE SOT363-6 (6-PIN package) as shown on page 34. Try Digikey or MOUSER.

[Rolin]

Re: Toshiba A665 blown MOSFET

Yes, a real team effort! b700029 did mention this earlier as well. Thanks to both of you! Now I just need to find the part.

Yes, it is getting late, and a good time to call it a night with success.

[budm]

Re: Toshiba A665 blown MOSFET

"Checking Q31 when ON. PIN1-3 (1.5V), PIN4 (14.85V), PIN5-8 (1.5V)"

"I now have 19V on Pin4. on Q30" Can you please verify that again? It looks kind of high, I expect about the same (around 15~16V if VSB is about 19V) as Q31.
Need to check the value of the voltage divider R410 (47K), and R423 (200K)

[Rolin]

Re: Toshiba A665 blown MOSFET

Thanks Budm, I'll recheck the Pin4 voltage again tonight. How do I find the R410 component? I looked all over the board last night and couldn't find it. Any ideas on how to locate it?

[budm]

Re: Toshiba A665 blown MOSFET

It should be closed by Q11 PIN 6 or Q30 PIN 1, 2, 3.

[Rolin]

Re: Toshiba A665 blown MOSFET

Quick update: I just verified the board POST's with Q11 PIN6 lifted. The voltage on Q30 PIN4 is indeed 19.3V. So I understand that is higher than Q29 and Q31.

You asked me to check R410. I guess I'm lost on this. I don't see any labeling for anything like R410. I uploaded a picture of the board and a closer image of the Q30 area in posting 11. Can you see anything that might be R410, but just not labeled? I see what appears to be a resister labeled 471 - I measured it (but didn't write it down) and it's around 5.2V. Other than that, I might need some help locating it.

BTW: There is a very small component, black color, right below Q11 Pin3 and next to Q30 PIN4. That measures 19V on both sides when the computer is plugged in but OFF. Any significance?

[Rolin]

Re: Toshiba A665 blown MOSFET

I looked at the schmatics and noticed that each Q29, Q30, and Q31 all have a resister like R410 in their circuits as well. Q29 has R409. Q31 has R411. Q30 has R410. I looked around each of these chips on the board and noticed they all had a resister labeled "471" next to them. Could this "471" be R409, R410 and R411? If so, it measures around 5.2V when ON

Nevermind... I just looked at the schematics again, "471" is most likely R406, R407, R408 if I'm reading correctly. R409, R410, R411 are different values.

[budm]

Re: Toshiba A665 blown MOSFET

I do not see any picture. Please do this, measure resistance between pin 4 of Q30 and Ground, it should be about 200K Ohms (this is the 200K Ohms resistor from pin4 to ground which is part of the voltage divider). measure the resistance (set METER to 200 Ohm scale) of that small component, one probe on pin 4 of Q30, another probe to one end of this small component, if it is R410, then one end will show 0 Ohm between its end and pin4 of Q30.
Those resistors for other Q has difference values for each Q.
471 = 470 Ohms, does not sound right.
The reason I worry about this high voltage reading is that I want to make sure it will not damage new Q11.
We can measure the sinking current by setting your meter to read DC current, set it to 200mA scale, black probe to ground, red probe to pin 4 of Q30, BECREFUL NOT TO SLIP THE PROBE, see what DC current you will read.

[Rolin]

Re: Toshiba A665 blown MOSFET

"BTW: There is a very small component, black color, right below Q11 Pin3 and next to Q30 PIN4. That measures 19V on both sides when the computer is plugged in but OFF."

I just measured resistance of the small black component and it measures 47 K ohms, this must be R410?

I'll look at your last post and comment in a sec. But you don't see the 2 pictures in my posting #11?

[budm]

Re: Toshiba A665 blown MOSFET

No I do not see any picture on the post at all. Did you use the attachment function?
If that is the resistor, then one end should be connected to pin 4 of Q30.
OH sorry, post 11, was looking some where else.

[budm]

Re: Toshiba A665 blown MOSFET

That resistor with 471 is real big, a lot bigger size than I thought, does not look like 47K resistor, more like a power resistor. The board does not have any designator for resistors printed on it at all!.
I thing the 47K and the 200k resistors at the bottom right of Q30 by pin 4 are the two resistors we are looking for.

[Rolin]

Re: Toshiba A665 blown MOSFET

265.3K Ohm between Q30 PIN4 and Ground. My meter is Digital with no scales. I already checked that little component and it is directly linked to PIN4 of Q30. It must be R410.

Still need to do this: "We can measure the sinking current by setting your meter to read DC current, set it to 200mA scale, black probe to ground, red probe to pin 4 of Q30, BECREFUL NOT TO SLIP THE PROBE, see what DC current you will read."

[budm]

Re: Toshiba A665 blown MOSFET

OK, we do have correct resistors in the circuits. the 265K reading is higher that what the diagram show, the main one I worry about is the 47K, that is the one that will limit the current flowing through Q11A, so we are OK now.