all right so this is a this is a water
damaged iphone 6 with prior repair
attempt success success there's a water
damage success with a prior repair
attempt so let's talk about how we would
start so let's all start together with
just a visual microscope exam so we're
gonna we're gonna look here and let's
see what you guys think we're gonna look
for any kinds of signs of water or
corrosion that are on this board so
let's look around and you guys tell me
what what you think here
alright let's flip over you don't see
any signs of water around here this is
sort of a hot spot typically no water
hmm
I'm looking for this kind of you know
oxidation possibly there but very minor
if any okay mm-hm
all right and then somebody's been here
all right so what we're learning now is
that alright so so these caps here were
we're missing the these these two here
one two one two so those are missing
alright so so let's let's let's let's
think about that because we wanted this
is a story and we want to understand the
the thinking that went into this board
before it got here because that is a
variable and that's part of our repair
process so now I don't you know now
we've kind of gotten to a point where
where we need to ask why would someone
have taken off all of these caps around
here so in my judgment just from looking
at this board I think the likelihood
that any of these caps needed to be
replaced you said you saw pictures there
alright let's look at that that would be
important
okay all right so while that's coming up
let's think about what do these caps do
so this these two caps here are on a
line that if we looked up in the
schematic by looking at the board view
and saying oh that guy's name is C 2020
and so they'd be schematic tell me about
C 2020 it would tell us the name of a
circuit that that C 2020 is on and it
was and it would say pp underscore GPU
pp underscore GPU now let's try to guess
what do you think what kind of us what
kind of a thing is that PEP power of the
GPU sounds pretty important power of the
GPU okay so if we were to you know then
we would have to say well okay power to
the GPU what why would someone take a
capacitor off that line what problem do
you think they'd be trying to solve
they think it's shorted yes exactly so
capacitors if we looked at a schematic
we could see that they all have one foot
on a line and the other foot on ground
in general on on an iPhone how does it
so a capacitor then a normal capacitor
is on a circuit and it has one photon
ground and then it has an insulation
space and then it has another foot that
is on whatever circuit on the line and
if you were to like get out your you
know electron microscope and see how
these little ceramic capacitors are
built you would see that they are they
are you know the side that's on the line
the side that's on ground have little
metal plates that come very close
together but they don't touch so there's
an insulation space between them so you
tell me how do you think they fail they
touch
so therefore the capacitor becomes a a
wire it becomes a wire yes exactly so a
capacitor can fail by becoming in wire
now once that wire is created now what
happens to the line it's always
connected to ground exactly so that it's
always connected around so what hap
to the voltage that's in that point and
so therefore if you use the multimeter
to say what voltage do I have here what
would it say it's always going to say
zero regardless of what it's supposed to
be now do you think that a voltage is
important for a line called pp
underscore GPU yes that will put that in
the category of you know if that's
actually a problem we need to solve it
so we we would be very interested in
whether or not that line was actually
short or not so let's think about this
it strips up all kinds of people all
over the time this is a number one
misconception in board repair and that
is on on any on most of the lines in the
iPad and the iPhone or in the iPad we
would be able to kind of come up with a
relative measure of the overall
resistance of the line to ground
resistance to ground now if something is
a wire to ground resistance as higher
level low exactly be like zero
resistance to ground would be zero if a
line was a wire to ground meaning a
short to ground had a short circuit
packed around so not on a normal line
what would we expect if we were to just
measure straight up resistance to ground
what kind of number would we expect I
don't know 100 kilo ohms or you know 500
we don't know if something like that was
some kind of a big number right now and
that's that's true for most lines that
are gonna carry a voltage and they're
going to send currents and they're gonna
have some sort of resistance to ground
however there is a caveat so let's think
about let's think about the good old
owns lost stuff so let's think about
voltage and once think about current and
let's think about resistance all right
so let's get in our mind an idea of what
voltage is so what is what is voltage we
have to go for some kind of analogy
pressure I like it a push a pressure so
voltage let's think of us a push brush
like right now it's your house back at
home you probably have the sink is
turned off in your kitchen if you were
to take some kind of a device and
measure the water pressure back behind
your sink would there be water pressure
in the pipe behind your safe
water pressures present no what about
current flow do you have any flow right
now hopefully not right
so pressure voltage it's just that push
but it's not gonna do anything it's not
going to actually move electrons unless
you have a path and so when you turn on
your your faucet on your sink you're
creating a path the pressure pushes
electrons and you get current so current
is miles per hour flow electrons
actually moving through through a wire
all right now let's think about in a
line like the main artery of the phone
the voltage the typical voltage is about
the battery voltage and who knows what
is the battery voltage for an iPhone 3
point a something 3.8 4.2 something in
that range so three point eight is the
push and then you're gonna get a certain
amount of current miles per hour that
you could measure and you could measure
that and it would be you know some
somewhere in the you know milliamp kind
of range right except for this very very
special lines that power cpus and gpus
so if you live on the schematic the
actual miles per hour in one of these
CPU or GPU power lines is very high the
actual current is very very high so what
do you think the voltage is gonna be on
those lines high or low what well if you
were gonna ask me I see a lot of cars
driving down the highway so what's the
push well it's gonna be a big push
because they're moving real fast that's
what I'd think right but that's not how
it is so the actual voltage on these GPU
CPU power lines is guess what it's less
than 1 volt like 0.8 so that push and
yet the the current is a massive
powerful the highway tractor trailor
buzzing down that route so how would
that be possible then how could such a
Dell lead to low resistance yeah it's
really only gonna happen if the wire
then it's really like butter
right it's gonna have to be iced so that
a tiny
push it's gonna you know make me current
why so just from knowing that then let's
make a prediction just on a normal phone
normal GPU power line what do you think
I'll get if I measure resistance to
ground of that line higher love I'm
gonna get low right I'm gonna get low in
fact I might get something that's so low
it almost looks like zero is it super
low it's just naturally really really
low and so that is how we get to the
common newbie mistake because what do
people think when they measure low
resistance they think short to ground I
found in short the grounds low
resistance the ground so short to ground
that's a problem I better fix it and
especially if you combine that with the
physical appearance of that cap with
green what are you gonna do then you're
gonna think I have a short to ground on
PP underscore GP here and I think it's
probably this gap so I'm going to take
it off so what we had missing then were
one two which are on PP GPU and then we
are missing these two and these two so
here these two a and B if we look up and
say what are those rails
it says here one of them is called PP
GPU and the other one I can't tell it
has a one so now we have one of the
other things that was missing couldn't
have possibly been the problem all right
but these guys here these guys are on a
different line all right so these guys
are on a different line and the name of
the line
it's called pp VCC main alright what do
you guys think pp VCC mains
sounds like pp+ power VCC okay this
sounds like main artery main power rail
and experience tells you that that's
certainly okay so this is the aorta
alright so how important is the aorta
definitely important so now if we
actually have a short to ground on the
VCC main the main power rail then that's
a definite problem that's going to be
why the things not going to turn on you
can't have zero resistance to ground on
the aorta you can't have a hole in your
any order when it's trying to pump blood
it's just gonna sit there and bleed out
that's a big problem and so if that was
the case that we actually had a short on
that power line then we would definitely
want to find out why and see if we could
find it's anybody wire that we can just
clear so that does make sense
and so these two guys were then missing
presumably - presumably because someone
measured and knew that they were trying
to solve that problem and not just
randomly because of physical damage but
now we we don't really know let's assume
that they did have a VCC main short and
that by removing those taps that
actually solved that problem so in that
case then you might get the the phone to
turn back on so now we've got a little
bit of a picture of why what was done
was done and and then it when we get
back down here this guy is on a
completely different rail as well so
it's it's again unclear that's on an and
power rail needs to be there but you
know just kind of taking that guy off
unless there's a short it doesn't really
make a lot of sense
alright so that's where we are now okay
physical exam is over findings are a lot
of prior repair attempt not a lot of
corrosion and we don't really know what
the current status of this board is at
all as far as is it going to power on so
what should we do next
yeah so we start with rule number one
what is rule number one
rule number one and this is what I made
up kind of recently and I really like it
well number one is is you don't have a
board problem until you know you don't
have a parts problem you don't have a
board problem until you know you don't
have a parts problem maybe you have a
parts prob maybe it's boards fine we
don't know right so rule number one so
we're not gonna do a goddamn thing to
this board until we rule out rule number
one all right so that means we need some
no good parts all right dude do we have
a DC power supply great all right now
this is gonna be hard we need to prompt
to boot and turn we need to be able to
see this here's what we want to know I
want it how am I gonna how am I gonna
make this DC power hookup to simulate
the battery what am I gonna do all right
I got a vote to say where is the
positive side now how do I use my
multimeter to figure that out okay that
sounds like a great idea
what about continuity mode was that dude
whoa mofo
that looks like continuity mode alright
there we go alright so beep means I'm a
wire so let's ask the question your
ground which one of you sides of the
battery connector is a wire to ground
are you a wired around yes
are you a wire to ground no so what side
of the battery is this gold thing here
that's ground and therefore what's that
right so when what happens if I do this
this is the DC power supply can I just
do that
and I see so far no current consumed but
is that normal or not yeah that's
actually good though because if if your
phone is off in your pocket do you want
current moving and draining the battery
no okay now how am I going to prompt it
to boot I'm gonna with my pinky finger
so I can't do that man look at me right
now I'm gonna prompts I'm gonna try to
hit the power button alright
so now the rest of us we need to have
our eyeballs on the DC power supply
which is going to be too hard for us to
turn around right now DC power supply
says yes I'm putting three point nine
volts into this device and the current
is zero so I'm gonna hit I've got the
power button connected and I'm gonna hit
power power power power power button and
let go and it goes to zero it goes to
zero point zero five so 50 milliamps and
then it just kind of hangs out there
alright let go let's try again
so just lift one off all right stick it
back on so you guys can come look Reed
the DC power with us name we're
it up all right let's hit prompt prompt
prompt prompt prompt let go and it stays
again at 0.05 so 50 milliamps all right
my next question would be well I you
know I'd like to see whether or not I
get the same or different behavior by
prompting it to boot the other way
what's the other way I can prompt the
phone to boot plugging it into USB yes
so who had the USB power bank great all
right back to you expect to work
do you remember which one's ground
ready okay so we're at zero that's good
so we're gonna just prompt to boot with
us be prompt prompt prompt prompt and
pull it out and it doesn't seem to
respond prompt prompt prompt prompt pull
it out all right let's look at the
connector and see if that's so when a DC
power supply does nothing like that that
generally means that that there is some
kind of a like is that thing on all
right all right from prompt prompt I
still don't see it okay okay so when we
turn up the USB power back on and prompt
it to boot it goes to the same 50
milliamps so both ways it does the same
the same findings what does that mean so
what category if a problem is that
there's your choices actually where's my
phone
what I'm going to show you guys all
right let's pass that over so that you
guys can see what normal looks like
don't forget my phone ready prompt
prompt prompt and I see Apple logo and
we can you guys come around we'll see
how the DC power supply is thank you can
you can see what it does ready here we
go
for a power button prom prom prom watch
what it does it's 240 milliamps we'll
assume that it would have here we go
it's hard to to have this one there
alright give up so the normal phone is
going to consume a EKG of current and
this this one would would likely do that
so what can we learn here so what kind
of a problem do we have then overall do
it does it sound like there's a short
circuit and we have rampant current
running to ground or does it sound like
we have you know an open circuit or is
this phone kind of a brain-dead phone
that's it it's a right now it's a
brain-dead phone it is not able to to
tell it's not able to issue any
instruction so it would be kind of like
the you know the school principal and
the PA system instead of saying everyone
please stand up we're gonna say the
Pledge and today we're having chicken
nuggets with the you know chocolate not
instead it's just and nobody knows it
nothing happens because there's no
instructions that that can be had
you