Guys, how are you? Welcome to a new episode of
Edgar and his crazy phones
How are you? Glad to see you smiling because here we are with more content
I didn't have any introduction prepared today, oh well
I'm happy that we are here, about to learn something new today
one of the most frequent questions people ask me is
Edgar, I have a phone that doesn't have signal
*#06# and there's no signal-- whoops, that's not it, this is something else
this
so, we dial *#06#
this stays in "searching"
and it doesn't have SIM card
I have already disassembled this phone
so it is disassembled
and it says "searching", but
it doesn't have SIM card, so, I'll unlock my tablet to
explain you something that I've explained in many, many videos
but people still ask about it
I see that lately it has become fashionable what we're going to call "The Magic Solution"
"The Magic Solution" consists in search an image in internet, for example "I have an iPhone that doesn't have signal
just change this circuit and it will work" that's what we're going to call "The Magic Solution"
that doesn't work at all
it's like saying "I dropped my phone, just change the display and that's it", no
we are entering a world where we must know how the circuits work
or how something works, so we can fix it, if not, we'll make mistakes
This is something that I emphasize in wanting to teach, please, let's pay attention
share this vide, subscribe to the channel, you'll learn a lot
we must remember that we have a Baseband CPU
Baseband CPU is a CPU, so it should have a PMIC_RF
and here it should have some of these called WTR or Transceiver, and here I'll put some PA
and here I'll put the antenna
How does this works? I've explained this many times
The PMIC must send feeds to the Baseband for it to operate
it also sends some of them to the WTR
this is for processing what is coming into the antenna
the antenna could say "Oh I'm connected in 3G"
so it connects to a 3G PA
sends the information to the WTR
and WTR is in charge of communicate with Baseband and communicating with each other
or vice versa
this is speaking on a large scale
So, why I'm explaining this? Because we could have 2 possible failures
two different radio frequency failures, one would be if the phone doesn't pick up a signal
with any company
or if it doesn't recognize the Baseband, these are two different things
if I dial *#06# is because I'm asking to the Baseband
I'm asking to the software, the software to the CPU, whatever, but that question goes to Baseband
the Baseband should respond with the Serial Number
if Baseband doesn't respond with the Serial Number
is because it is dead, and if it is dead
it could be because the RF PMIC is not working
or some WTR is blocking it
or anything, it could be that this one
is broken in some of the pads
but I have to make the Serial Number recognizable
so it's very important to do that
now, if this shows me the Serial Number, that means the Baseband is alive
but
the PA along with the WTR and the antenna cannot pick up signal
So these are two completely different faults, two faults that if we know
the difference between these two, we would be able to diagnose it
Here I have this phone
it doesn't pick up signal
if I dial *#06#
it just doesn't show the IMEI, and says "No Service"
that means that the Baseband is not being recognizable
so
let's start with the diagnosis of this phone
Where do we start, Edgar?
in a moment I'll tell you
I'll take the board off
no one has touched this phone
let's do something here, let's remove this very carefully
and we can see this is a QualComm, is the series that most fails with these models
let's go to the microscope
and here it is
a QualComm series phone, now, what are we going to do?
is important to measure to find shorts, because one short in some line
of PMU can
leave the PMU inoperative
so, let's put out multimeter in diode mode and measure to find shorts
ok... no
we don't have any shorts in here
now that we know we don't have shorts, what are we going to do?
I'll remove this shielding
and let's measure some power suppliers for the Baseband
for that, I have to remove
this shielding
ok then
I have to remove the shielding because here is the Baseband
so, let's heat this up
ok
there it is
let's put this aside
and clean this
perfect, now what are we going to do?
Remember that PMIC of RF is in charge of powering the Baseband by Bucks
those Bucks should have a coil, so
it is important to check if any of those lines is leaking or not
the values are about 300
this shows 170, we'll see something
300
this shows 96 but I know this has a low resistance but,
this one
this one shows 200, 237
this one 400
and this one 300, this shows 252
let's wait for this to cool down
you can't see me, but I'm looking for another board
another board of iPhone 7
here's another one, it's important because we can't just make things up
so, it's very important that we have
functional boards
to take some measures
for example, now I'll grab another board
Whoops, this is an iPhone 8, sorry
I'll look for an iPhone 7 board, give me a minute
here we have a board of iPhone 7
let's measure the same line to see
what's the voltage drop of this line
I think is this one
369
and this has... this was hot when I was measuring, probably it was just that
300
400
and 300, ok
it's fine, we don't have any leaking lines
so, now
let's talk a little
I have the PMU and doesn't have a line in short, doesn't have leaking lines, so
it should turn on and send the voltages
so, what we're going to do is
turn on the device
here I have it, let's measure for the last time the lines and see if there's not a voltage drop
400
300
400
300
I'll measure again and look for shorts, sometimes
they suddenly appear
ok, everything is fine, now, what I'm going to do?
Let's
turn on the device
let's turn this on
I'll look for an alligator
to connect it to the negative, ok
I connected it to the negative
now I'll connect it to the multimeter in the negative
now my hands are free
let's turn on the device, here it is turning on
and what I want to check is if I have voltages
let's see if I have voltage in the coils
let's see this under the microscope
let's see if we can find a voltage here
for now I don't have any voltage
that's bad
but at the same time that's good
I don't have any voltage
let's see if this is working
I think the alligator isn't working
I think it wasn't working because of the alligator
there it is, now it's working, let's measure this coil
we have 1 volt here
we have 1.2 here
we have 0.9 volts here
we have 1.8 volts here, and this won't have any voltage because this works until
we have connected the SIM card
so, if you notice the PMU is sending the voltages
I'm just measuring these 4 voltages
with this I could know very times
the PMU of RF
in some moment is working, so
What else are we going to do? We'll measure the coil switching with the oscilloscope
this is pretty easy to do
let's see if
I can put a camera to show this, give me a minute
I'll tell you
Well, I guess you can see something here
but, excuse me, that's going to look like that for a moment, so
what I'm going to try to do is, touch here
the coils, and see if the coils are working
that they're doing well the switching
the device is on
so
let's change to this camera
if you notice, here we have
a coil
working well
it's working well
this is not working... there it is working
and now I'll touch this one and it is working
ok then
The coils work perfectly
I just measured them with the oscilloscope like this
I just put this to Ground and start touching with the oscilloscope tip here, there it is working well
here, there it is working well
and here
there it is working well, and this one will be not switching because
Well then, back to the subject
We have already checked the power suppliers
we already looked for shorts
we already checked if the coils are switching and the phone just doesn't show the IMEI
so, now let's go to the tablet once again, to do a little drawing
so, let's see here
if I have the power suppliers here
and said OK
Right? Because we measured some of them, but that's enough to say that the PMU is, theoretically, OK
WTR doesn't turn off the PMU because I have the voltages
so, who's next?
I may have a crack in the Baseband and that's why the phone simply does not pick up a signal
so
I'll not make mistakes, if I see the PMU working, if I see
in this case, the voltages and the coils switching
everything is fine, but Baseband doesn't respond, so it could be that the Baseband is cracked
So, what are we going to do? We'll remove the Baseband
do reballing to de Baseband, place it again and check if that works
this is a somewhat long job
we'll do the process, the diagnosis has already been done
we'll do the process in quickmotion, so, let's start
We have finished
here we have the phone, now let's go to the microscope
and let's put
here, we can see this is the phone
that we repaired
so
if I remove this
get in the phone
dial *#06#
there it is the IMEI
well, I don't have the antennas connected, but
there it should work
so, we repair a phone without making any mistakes
without removing circuits that we shouldn't have removed
That's because we have a protocol of measures, here we don't have "Magic Solutions"
here we are not guessing
it's not like "I've seen someone repair a phone by making jumpers in some Grounds and that solves the problem" no
here we do exactly what you need to do
I can't lie, but we can make mistakes because we're humans
we can make mistakes and we could misinterpret a failure
and remove a circuit that we shouldn't, but
many times, if we can interpret it in a good way
we stop making mistakes, so
this was just reballing the Baseband
a very common repair
many times this may not be the solution, probably the Baseband is not well reballed and that is why it does not work
many times it's because the Baseband is leaking, many times it's because we have no voltage
many times because a coil works saturated
many times
a transceiver is shorting a line
we have many options in radiofrequency, but we need to know where to look for the fault
So.... it's going to rain?
it's going to rain
So, for me, a pleasure to be here helping you with a new video
always to continue contributing to this beautiful community
take care and we'll see you
drum roll
in the next video. Bye!