Ideapad 300-15isk nm-a482 oscillating B+

[mastsrl]

Hello,
i have this motherboard that won't turn on even from battery.
checked the schematics and i'm seeing quite strange behaviour:
The adapter in drops in voltage from 19v to 16v~ every 1s or so, as if there's a short or something dropping it(but it's variable), nothing in the board gets even warm.

The voltage at point P2 between the input mosfet PQ301 and PQ302 is nearly 0 and spikes to 18v for a split second and goes back to near 0, odd thing is that jumper PJ301 which is the output of PQ302 has the same oscillations but this time they go up to 15V approx and then slowly drop to ~10V until it spikes again one second later, just like the input.

none of the +ALW regulators have output, as if none of them are enabled.

i'm kind of at a loss i always understood that the always regulator are just that ALWAYS, if they depend on the EC_ON pin that comes from the EC, how can they even start if the EC is powered off until it has VCC/ALW (a chicken and egg problem, how do you power the EC to get the enable signal when the reg that powers the EC is off).

¿any ideas?, the usual suspects which are the totem-pole input FETs don't look like the issue because it's making the adapter drop

[mcplslg123]

Re: Ideapad 300-15isk nm-a482 oscillating B+

Check for a rusted, shorted or bad resistor in voltage divider circuit of dc in mosfet's gate.

[ktmmotocross]

Re: Ideapad 300-15isk nm-a482 oscillating B+

EC is powered from 5v/3v ic, before 5v/3v is generated.

always is not always in newer laptops. first they swithed 5v and now it switched even 3v. all for saving power

[mastsrl]

Re: Ideapad 300-15isk nm-a482 oscillating B+

EC is powered from 5v/3v ic, before 5v/3v is generated.

always is not always in newer laptops. first they swithed 5v and now it switched even 3v. all for saving power

Okay small update and a snafu on my part, i think the power brick i was using is wonky, so i powered up the board with a bench power supply(the standby consumption is below 0.5W, so no shorts), now the oscillations are completely gone!, and i have solid +19V on B+ which means the input mosfets are being driven correctly.

But i don't have ANY of the ALW rails, all the ALW input jumpers have solid 19.9V

Which +5/3V IC?, how is the EC even powered on in the 1st place without the regs?

i'm checking the datasheet and the EC is powered on by +3VS, on p46 there's a switch that says "+3VALW To +3VS LOAD SWITCH", which means the EC VCC is converted from +3VALW.

waaaait i'm spotting a +3VL in the power schematic, that's generated from the LDO of the same sylergy reg(which i can't find a datasheet of) that makes +3VALW, one output is +3VLP which is jumpered to +3VL on PJ404, and that +3VL goes into the VSTBY0 of the EC!, bingo!.

Same deal with +5VLP

edit2: +3VLP is dead, going to try and bypass it with an external supply

[mastsrl]

Re: Ideapad 300-15isk nm-a482 oscillating B+

Ok did more troubleshooting, using an external power supply injecting 3V into the +3VLP jumper brings +5ALW and +3ALW back online, that's one regulator blown already (the LDO part of the SY8286), but the motherboard still won't turn on.

More checking and now i see that i'm missing +1ALW, desoldered the output jumper to see if there was some sort of short (as i felt warm in that area at the output where there's another small mosfet) but the output of the regulator remains at 0, so that's another potentially blown reg.

next step is to use another bench supply to inject +1V there and see what happens, but i'll have to followup on that next week

[ktmmotocross]

Re: Ideapad 300-15isk nm-a482 oscillating B+

that because u injecting, but there is more comunication between chips than only voltages. dont inject but change chips. injecting is only good for finding shorts. with injecting u can do more damage

if u have pulsing main rail, that means something is telling charge chip that something is bad and he turn off power. so start measuring charging ic

but first flash bios. lenovo have many problems with bioses

[mastsrl]

Re: Ideapad 300-15isk nm-a482 oscillating B+

i can't go changing rare components willy-nilly, i have 3 regs out of order, all of them rare chips that are quite costly and/r take 60+ days to arrive.
In the past i've always had success using external power supplies to troubleshoot failed regs, plus with the jumpers you can isolate them.

In any case, injecting +1V also did not make the computer turn on, this motherboard has been declared "beyond economic repair".

the pulsing might have been the power brick, as the input pulses as well.

[ktmmotocross]

Re: Ideapad 300-15isk nm-a482 oscillating B+

it is beyond YOUR knowledge of repair

u have done no measurement and show no effort for repairing this one



and dont put that crap about expencive chips on us. we know what these chips cost. it is VERY CHEAP

[mastsrl]

Re: Ideapad 300-15isk nm-a482 oscillating B+

i have done all the power rail measurements as i've stated in my previous posts.
I don't know where you live but where i am, these chips are not cheap and/or are not available. ONE of the regs is being sold for 4 times what's found on ali (and that's dollars, in our currency it's extremely expensive), the rest directly don't exists and i'd need to buy them from aliexpress, which means 60/90 days. and even if i change all of them there's no guarantee this will work(most likely it won't as the test i've done show)

[ktmmotocross]

Re: Ideapad 300-15isk nm-a482 oscillating B+

u measure power rails and that is all? damn u put so much work to it.
did u measure charger ic? no? but this ic is culprit fot main B+ rail

chips from ali came to 30days

yeah. better tell it is economic expencive


next time dont ask for help if u dont want to repair. u r wasting others time

[Tom1392]

Re: Ideapad 300-15isk nm-a482 oscillating B+

I'm facing a similar issue, 3v ldo sy8208b is getting short circuited as soon as replaced. Its all because of an experiment gone wrong.. i tried to power the laptop from a boost converter and inbetween messed up with polarity. Dont know what else has blown up apart from the ldo.

[Tom1392]

Re: Ideapad 300-15isk nm-a482 oscillating B+

Anyone with a past experiency of pu401 sy8208b shorting

[ktmmotocross]

Re: Ideapad 300-15isk nm-a482 oscillating B+

what rail is shorted when replaced?
check mosfets for shorting between gate and source/drain

[Stil86]

Re: Ideapad 300-15isk nm-a482 oscillating B+

I have a similar issue but no one component burn and the display flash from off to black.
Notebook self power-on if ac adapter connected but not with batttery.
Tryed on battery, on ac with different ac adapter, the same problem.
Tryed another display and another edp cable, same problem.
On U5 pin 1(OUT) and 4(EN) I have oscillating voltage from 3v to zero.
Any idea of some trying ?
Thanks

[ktmmotocross]

Re: Ideapad 300-15isk nm-a482 oscillating B+

So ic is good but have bad EN signal. this signal is generated by cpu so u must find fault elsewhere. check R1 if have right resistance.

but as first flash bios

[Stil86]

Re: Ideapad 300-15isk nm-a482 oscillating B+

Thank you for you answer, if R1 is the resistor between U5 and the CPU fan it is 99KOhm so it is ok.
How can I flash BIOS on this laptop if I don't have an IC programmer ?

[Stil86]

Re: Ideapad 300-15isk nm-a482 oscillating B+

Ok I have an easy Jtag Plus ...

[Stil86]

Re: Ideapad 300-15isk nm-a482 oscillating B+

Update: I have backed up the content of the rom, erased it and flashed the bios taken from here: https://www.badcaps.net/forum/attach...2&d=1505624641
If I plug power cord the laptop automatically power on, with the battery I have to power ii on with the button.
Now the tension on U5 is stable but the screen remain black (not powered off, black).
Any ideas on how to proceed ?
Thank you