Ideapad 100 NM-A841, P channel mosfet on laptop in.

[tmaster21]

Hello guys. i'm having problems here with this lenovo 110 with board NM-A841 laptop. There is an P channel(pq302) and after it i start ,i have 19v but with time, it decreases or if i press "power on" switch or jumper j6 , it falls to 0 and back to 19v. There is no short and works good on battery, but won't charge or charge until the voltage drop like i explain after P mosfet.
Well i suspect that this mosfet is no good. if you look to skematic i have steady 19v on P2 but start to decrease on P3 like if the mosfet is dying . the gate of boot N an P mosfet are the same: is steady 17.7v.

i don't undertand really why is this mosfet here and why are the running at same gate voltage...can someone give me a light whas happening here?


skematic from here:
https://www.badcaps.net/forum/showthread.php?t=76971

[janocko]

Re: p channel mosfet on laptop in.

you can try to reflow with hot air blower IC OZ or PU301.

[mcplslg123]

Re: Ideapad 100 NM-A841, P channel mosfet on laptop in.

PQ301/302 are both P channel mosfets and their gates are connected together-so there will be same voltage on pin4 of both these mosfets. Since both are P channel,gate voltage should be lower(5V-12V) for it to work. You are getting +19V at P2 'coz the PQ301 has forward direction diode(inside mosfet) but it cant reach P3 as the diode is in reverse order or blocking mode in PQ302. So you need to fix gate voltage of both PQ301/302.

01.
Check resistance between
pin1-4
pin4-5
pin1-8 for both PQ301/302.

02.Try removing PQ304/305(they are there just for protection)

03.Check resistor value for PR307/303 as they are voltage divider circuit for Gate pin voltage.

If the issue persists, then measure voltage on PQ307/315 and post here. Dont reflow or heat up PU301 without finding the root cause.

[tmaster21]

Re: Ideapad 100 NM-A841, P channel mosfet on laptop in.

PQ301/302 are both P channel mosfets and their gates are connected together-so there will be same voltage on pin4 of both these mosfets. Since both are P channel,gate voltage should be lower(5V-12V) for it to work. You are getting +19V at P2 'coz the PQ301 has forward direction diode(inside mosfet) but it cant reach P3 as the diode is in reverse order or blocking mode in PQ302. So you need to fix gate voltage of both PQ301/302.
.

Exacly what i think ... so this pq307 receive PACIN signal and shoud starting ground the gate for this mosfets start work. that's it? but i dont understand if the pq302 diode is reversed it will conduct forward to p3??

resistors are ok.
datashet from pq302 (4455) says vgs Threshold between -1.5v and 2.6v so power suply its around 20v - 17.7v from gate its 2.3v. Shouldn't be that gate ok for hold the mosfets running???

[mcplslg123]

Re: Ideapad 100 NM-A841, P channel mosfet on laptop in.

PQ307 should receive PACIN high(Gate). Since the gate is high, that will turn on this N channel mosfet resulting in Source(GND) travelling to Drain. Drain of PQ307 is connected to PR307,pin2. A voltage divider will work when one end will receive voltage and the other vend will be ground. In this case PR303 is your R1 and PR307 is R2. R1 & R2 will act as voltage divider when pin1 of R1 will receive 19V and pin2 of R2 will be grounded. Going by the voltage divider formula you should get 4.82V at gate of PQ 301/302.

Your understanding of mosfet datasheet is not correct. perhaps you need to learn more.

Our mission is to help as many members in whatever way possible but we really cant teach complete theory/principles here. You need to understand what is blocking mode concept in mosfet. I cant explain everything here in detail.

I tried my level best to explain how gate voltage of PQ301/302 will work.

[tmaster21]

Re: Ideapad 100 NM-A841, P channel mosfet on laptop in.

PQ307 should receive PACIN high(Gate). Since the gate is high, that will turn on this N channel mosfet resulting in Source(GND) travelling to Drain. Drain of PQ307 is connected to PR307,pin2. A voltage divider will work when one end will receive voltage and the other vend will be ground. In this case PR303 is your R1 and PR307 is R2. R1 & R2 will act as voltage divider when pin1 of R1 will receive 19V and pin2 of R2 will be grounded. Going by the voltage divider formula you should get 4.82V at gate of PQ 301/302.

Your understanding of mosfet datasheet is not correct. perhaps you need to learn more.

Our mission is to help as many members in whatever way possible but we really cant teach complete theory/principles here. You need to understand what is blocking mode concept in mosfet. I cant explain everything here in detail.

I tried my level best to explain how gate voltage of PQ301/302 will work.

Thank you. this explanation confirmes my doubts about this p chanel mosfet with reverse diode. i know they are used for reverse polarity protection here ,bus i was in doubt about the working principle here. know let me see whas happening on this gate for i have so high value o mosfets gate. (yes the laptop stills here waiting for i finish it...). always confirm every doubt before reheat and brake everything X)

[tmaster21]

Re: Ideapad 100 NM-A841, P channel mosfet on laptop in.

@mcplslg123
you are the best! SOLVED!
pq304 was in low impedance ,causing that i measure 10k on the pr303 - 200kohm pr303 resistor. i thought tha was the resistor but was the transistor. now gate voltage = 5v ✓
but i'm not getting ..why are there transistors here(pq304 and 305), protecting what ? PACIN send pq307A to ground and they conduct...than means mosfets only work if there is pacin present?for what is that? pacin is the one that activate the mosfets anyway...

[mcplslg123]

Re: Ideapad 100 NM-A841, P channel mosfet on laptop in.

Pleased to know you solved it. What i have told is simple basics and certainly not rocket science.

Yes PACIN will ultimately lead to correct gate voltage on dc-in mosfets depending on rest of the components are working. PQ304 and PQ305 are part of protection circuit and both of them are different(look at direction of arrow in PQ304/5).You need to understand how NPN and PNP transistors work and i'm sorry i cant explain them here in detail. there are youtube videos which you can watch and try to understand better.