okay so today we're going to be going
over an 820 2936 that's not turning on
so somebody tried to replace their own
keyboard and clean their motherboard and
it was working just a few of the keys
weren't working and after replacing
their own keyboard now it is dead so
let's see what's going on here so the
first thing that I'm going to do here is
plug in a charger with a fresh new dcn
board to see what I get and with a
different known good dcn board I get no
light in the charger no fan spin and no
anything so the first thing I'm going to
do here is I'm going to open up the
schematic and the board view for this
model machine so that you can kind of
get an idea of what it is that that I'm
trying to do here and what it is that
I'm looking at while I'm trying to
diagnose the cause of the problem so
let's go over to the schematic over here
and look at how this thing is supposed
to
work that's not the schematic that's the
schematic all right so what we're going
to do here is we're going to go to page
three of the schematic where they give
you this whole little idea of how
everything works so over here we have
the AC adapter in and that's going to go
to this chip which creates PP bus G3 hop
it's also going to go through this chip
which creates pp3 v42 to this chip which
sends power to the SMC uh I mean the
reset signal to the SMC which will tell
the SMC to turn on so let's get an idea
of what it is I get at a few different
points so when I go to try and measure
around this board I'm going to put the
voltage multimeter into voltage mode
over here and it's really I finally got
a C camera angle that works for me that
is not you know interrupt what I'm doing
but also allows you to see the
multimeter which is which is nice here
then what I'm going to do is I am you
know what it would actually be better
you'd be able to see the meter better if
I move this thing over a little and I
move it to the side so let's might as
well go ahead and do that
now yeah a little bit of a better
view all righty so now I'm going to
measure voltage on pp3 v42 now to find
pp3 v42 what I would do on this board
view software over here here is I let's
just see if I can get it so you can view
there we go so on the board view
software what I would do is I would type
n for Nets which is going to show me
every section on the board that a
specific rail comes up or a signal and
then type pp3 v42 G3 hot that is needed
for the one wire circuit if you don't
understand why please watch my one wire
circuit videos they're important if you
are going to understand this one I have
many videos in the one wire circuit
they're usually about 10 15 minutes just
watch one of them it will save you a lot
of heartache and trouble so I have 3.42
volts now the next power rail that I'm
going to check which comes in right
after the charger over here is going to
be PP bus G3 hot so let's check PP bus
uncore G3 hot now I'm not going to
expect to get anything there because I
don't have a green light I should have a
green light my uh you know I have 3.42
volts which is the rail that powers the
one wire circuit but you know I don't
have a green light so we're going to
have to look into why it is that I don't
have a green light
and of course ppbs G3 is at 0.2 volts so
the way the one wire circuit works is I
need to have a power at a certain
component and I also need to have a
signal at that component so this here is
adapter sense this is where the charger
is going to speak to the SMC on a data
line so the charger is going to come
into this chip on external then it's
going to speak to the SMC on the
internal pin cis1 wire goes straight to
the SMC in order for this chip to
receive the power that it needs to CC
pin to turn on it needs to have power
delivered to it by u901 and u901 is
going to take pb3 v42 and pass it over
here if SMC BC AC is present so let's
see if SMC BC AC is present so I look
for U 6901 and U 6901 is going to be
right over
here let's see is this what I'm looking
for that is what I'm looking for all
right so I am going to try with the
microscope now I'm going to take a look
at that area see what it looks like and
give a little measurement so let's get
the board under the microscope over here
so that you can see it so this is U 6901
and that area looks pretty nice looks
pretty fine looks like nothing bad
happened there except for my microscope
trying to run away so let's just tighten
the microscope so it can't run
away so let's measure so SMC BC AC is
going to be present right over here I
believe let's see so yeah right over
here so see it says SMC BC AC okay over
there so let's check it out and let's
see what I get on my multimeter when I
measure that pin so on that PIN for SMC
BC AC okay I get
0.00
volts I'm closed so I'm not answering
the phone right now so we get zero volts
there so where does SMC BC AC come from
so let's see where SMC BC AC comes from
so as SMC BC AC comes from the u700 chip
so let's check out the U 7000 chip in
other videos I've said that this chip
needs to receive four volts at charger
AC and before SMC BC AC will occur so
this is where ppdc and G3 hot which is
the power from the adapter comes in the
power from the adapter comes in through
here and goes to this voltage divider
from this voltage divider it's going to
go to pin 3 uh charger ACN over here so
let's see if I have voltage at Pin 3 of
U 7000 and please stop opening this on
the other monitor all right so U
7,000 find this and let's see where is
r710 and
r711 right over here so these two so
let's see if I have four volts over
there let's also see what that area
looks like on the
microscope
so these little red points over here
tell me a sad story for was something
that went on in this area so you see
that and you see that but let's take
let's go and go ahead and measure anyway
let's also get this microscope to a more
comfortable
position okay yeah swivel for me
excellent good stuff okay
so Focus there we go so let's
measure interesting zero volts very
interesting so we have 16 volts at the
top of the voltage divider but at the
other side of it I have
zero hm
now here's where this gets tricky the
problem is that we could have a couple
there's a couple of things that could be
going on here let's just go over the
couple of things that could be going on
here
so this chip the u700 could be pulling
it to ground this resist r7010 could be
bad r711 could be open meaning no I
don't know me open I mean
r711 could be at zero ohms r710 could be
at infinite ohms
or u700 could be pulling that signal to
ground now let's think a little bit
about the basic Electronics video series
that I did where I said how resistors
often fail resistors often fail to where
they are working at infinite resistance
so we can throw out the idea of r711
failing and becoming zero ohms pretty
quickly r710 could very easily have
opened and not be providing power or
u700 could be dead as a result of a
shock to it and it could be shorting
charge or AC into ground let's take a
look now what I'm going to do here is
I'm going to measure r710 and if r710
manages to be around 30 kohms then I am
going to jump to the assumption that U
7000 is bad just based on the knowledge
that I have on how these resistors often
die remember capacitors often die where
the capacitor itself has you know turns
into a wire they can very often short
but resistors themselves really don't
often short so what I see here is that
I'm getting 2622 khms which is really
close to the value on the schematic so
at this point I'm going to make the
assumption that my u700 chip is probably
bad and my U 7000 chip probably needs to
be replaced so this is where I'm going
to turn on the rework station and I'm
going to get started with removing that
chip and putting on another
one so first thing to do here is remove
my u700 chip which is this one so that I
can put on a new one now I have the air
filter on high and I have it located
right next to where I'm working because
I don't want to one ha any of this crap
and I highly suggest that you do the
same remember it doesn't matter what
other people tell you cuz nobody's going
to care about your health the way you
care about your health so if you're
doing this stuff use an air filter use a
fume
extractor and if you can't then at the
very least try not to inhale it do this
and go every time you get
stuck next to a bunch of nasty
fumes
my hacko FR 801 has removed it with
ease now we will prepare for placing a
new
chip so I got my nice hacko FM 2032 here
I love this
thing let's get rid of all the old junk
and okay too much solder on the center
pad is my Hallmark I should have Wicked
that but I didn't cuz I required
changing irons and I know I can get away
without any of
that okay the chip has been
removed new chip is about to be
applied way too much solder on the
center pad is my
Hallmark I really should stop that
habit it's
Heat get you somewhere on the
board here we
go nice try see how it's trying to spin
trying to change orientations on
me okay and I push down really hard the
most important thing here when soldering
the ISL 6259 chip the most important
thing is to make sure that you push down
hard so that the chip itself actually
gets solded on the board cuz you may
think it's soldered but then when you
look around at an angle you realize that
it's not
soldered that's what this really nice
hacko fm22 is good at is going around
and getting every single pin so again it
may look like it's solder from the top
but then you're going to look at it from
the side and you'll realize that it's
not actually
soldered it you know it's sitting on top
of a mound but one of two of those pads
isn't properly soldered so you know a
really important thing when soldering
these components to have them flat on
the board and when you have a center pad
it's really easy for it to float on the
solder on the center pad instead of
instead of actually falling a
place so even after I know that I've
pushed it flat on the board I go around
with this and I want to feel every
single pad I want to feel every single
pin I want to feel each individual joint
with my iron and you can actually and
you'll feel it you'll get used to this I
assure you you will feel
it and you'll know when you soldered it
on there properly
soldering this chip improperly because
of lack of knowledge or a [ __ ] station
are very common causes of frustration
and
failure so what happened here is I
plugged it in after replacing that and
as you can see I have a green light and
my fan is spinning which means that I
solved my problem so u700 here was most
likely pulling down my charger ACN
signal because it was [ __ ] and it most
likely got [ __ ]
by honestly who the hell knows I really
have no idea what people do when they
work on their own stuff but it was
[ __ ] and now it's not [ __ ] and now
it works and we have a happy 820 2936
ready to go back into a customer laptop
and that's that and I hope you learned
something oh and the last thing I want
to mention before I exit out of this
video because this is a common question
a lot of people ask me you know one of
the things I want to learn from your
tutoring class one of the things I want
to learn is how to measure each
individual component I want to know how
to measure this that or the other and
the reality is you don't sit here
measuring logic gates you don't sit here
measuring U7 thousands what you do to
fix these products is you just use your
brain you have regions and you have
theories and you have ideas and you you
try to turn those ideas into a working
solution so I know that sounds silly but
let's just look over here at this
particular schematic so if I were to
measure this resistor right let's say
I'm measuring the resistors the u700 is
shorted to ground right this is attached
to ground on one end so this resistor
r711 over here it's attach atted to
ground on one end so if I measure the
resistance of r711 with the [ __ ] u700
u700 is [ __ ] and short it to ground
right so that's over here shorted to
ground this end over here is also
shortage to ground so when I measure
that resistor you think I'm going to get
9.31 kohms no when I measure this
resistor I'm going to get zero ohms
because the U 7000 which this resistor
is attached to is short it to ground now
you may say well you could take the
resistor off the board to measure it
that's the right thing to do when I take
a resistor off of a motherboard that has
this many components that's this [ __ ]
small and I put it on the table you know
what's going to happen to that resistor
when I go to measure it I'm G to go like
this and I'm going to go Dink it's it's
going to fly it's going to go into the
sixth Dimension and I will never ever
see it again so you know a lot of my uh
my Diagnostics is not measuring every
single resistor measuring every single
capacitor it's just having a little bit
of an understanding of how the circuit
Works getting an idea of what happened
how did this fail why did it fail what
is some theories as to you know how it
failed how does what the board tells me
line up with my theories as to why it
failed for example having a little red
prob points around the chip and then
noticing that there are two things that
could be short it to ground the chip or
the resistor and then just having an
idea of how resistors work res how
resistors fail resistors usually fail
open where there is an open line and not
where there's you know zero resistance
just having all the stuff in the back of
my head is what allowed me to fix this
it wasn't really measuring every single
individual resistor or capacitor on the
motherboard using the multimeter so
again just to get just to get it across
you don't fix motherboards by measuring
every single component on them you
you'll never get anywhere you will lose
your mind you measure motherboards
through having a bit of an understanding
of how that board works how that circuit
Works asking yourself how you know what
do you think the fault was and then just
just figuring it out now I don't really
know how to explain it much better than
that