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Cell Phone Motherboard Repair course for beginners - mobile
ismall od academy
https://www.udemy.com/course/cell-phone-motherboard-repair-course-for-beginners-mobile/learn/lecture/30804014#content

content is all video

01 Introduction
01-01 Introduction
video starts off quickly. presenter has a removed cellphone
motherboard and a multimeter. "i'll show you how you can check the
switches".
- multimeter is set to conductivity buzzer
- cell phones have switches in them with two pins, ground and high
- conductivity with board ground is used to identify high pin
- when switch pressed, conductivity with high is present
~
ICs ... should not be hot? accent
~
capacitors
IC capacitors are small rectangular boxes with distinctive conductive
regions on both ends
a capacitor is a nonductive element used specifically for its
resistance to current; hence they should all be highly resistive
one side of a capacitor can be checked for conductance with ground;
the other side then should not be conductive with ground
~
excerpts to wet appetite
montage of probing chips and components and referring to and drawing
circuit diagrams and inspecting chip silkscreens

honestly it looks like what i used to do without knowing what i was
doing, lots of multimeters probing surfaces everywhere
i'm thinking if i get back into microhardware i'd want to start really
slowly and simply because my hands have maybe tried really hard to
break stuff; unsure; i'm hearing i can have a different story where
that doesn't happen so much

01-02 Cell Phone Motherboard Overview

cell phone motherboard
- same working principle as motherboard of laptop computer
- processor, graphic card, rams, mosfets, ics, capacitors, inductors,
diodes, connectors, slots, switches, camera, clock battery, ...
the presenter repeatedly points out categories of components such as
mosfets, capacitors. this helps the viewer learn to identify them.
shielding has already been removed from the example motherboards
each shielded area surrounds a circuit

02 Cell Phone Motherboard Repairing
02-03 Cell Phone Motherboard Architecture

- divided into parts, each part inside a shiny area that likely held a shield
- a part containing processor and ram, a part containing wifi and
bluetooth, always a circuit in a rectangle
- sometimes these major circuits are not divided by shielding pads on all sides

02-04 Cell Phone Motherboard Parts and Components

- big chips are always procesors and ram
- slightly smaller chips the lecturer calls ICs
- each of the separated circuits has an IC that is its controller
- smaller chips are then mosfets
- very small components are then things like caramic capacitors or inductors
- the presenter points out which items are ceramic capacitors, and
which are inductors. inductors on this board appear to be oriented at
90 degrees maybe coincidence, larger, wider, darker color
- inductors are checked the opposite of capacitors: they must conduct to be good
- for connectors such as the sim slot or the battery, check both the
connecting pins and the solder connections to the board; same is true
of switches
- damaged ICS are often indicated by shorted adjacent capacitors, or
by high temperature when touched
- bad ICS are hot in every motherboard, as a rule

- the first circuit is the processor and ram, lots of capcaitors [for
stabilizing voltage?]
- the second circuit is the networking and wifi
- then power management
- largest connector, sim slot
- camera, other connectors

- always do a visual inspection before doing anything. for example, a
bad component may be cracked
- larger square objects are chemical capacitors rather than ceramic,
all the same color
- inductors can also look round, there are other components like
sensor resistors

02-05 Cell Phone Motherboard Common Faults

- usually the usb or power connector fails
- replace the usb connector, but sometimes it is good and the solder
connection to the board is bad

- second most common failure is battery connector; broken pins
- check the connectors and the solder points

- same with the SIM connector, the pins can be broken or deformed
- same with the microsd connector

- then the switches can be broken, under the buttons
- their soldering can fail too

- the other connectors inside the phone, that connect the boards and
parts together, can also fail, or the wires break
- the cmos battery soldering can also fail

- the ICs then, can also be shorted, especially the power IC
- always check the ceramic capacitors around the ICs, that they are not shorted
- if the ceramic capacitors are shorted on both sides it means the ic is bad
- also check with your finger they are not hot
- shorted IC? replace it.

02-06 How to check switches serviceability
- this was in the preview at the start
- use the buzzer or resistance option of a multimeter
- find the ground and high pin with conductivity to ground
- verify the switch grounds the high pin when pressed
- replace failed switches

02-07 How to check ICs serviceability on mobile cell phone
- check failure by checking heat with finger; bad ics are very hot
- check ceramic capacitors around the ic are not shorted
- put the black probe of the multimeter to ground, and then touch the
red probe to both sides of capacitors around the ic
the ic is good if the caps are; if a cap is shorted then the ic is

[note that caps may give brief conductivity as they charge, but this
does not mean they are shorted]

02-08 How to replace failed components in cell phone motherboard
ICs and component references
Replacing failed or bad components, what component to choose
- The written numbers and letters on a process is called the
"reference" by presenter
an nvidia gpu has "NBF748-52P"
you can use the reference to find the replacement part
- presenter picks another circuit, unknown, but it has an IC with numbers on it
- the circuit can be replaced by another with the same numbers
- _every_ component has a reference

- a big square inductor can be checked with a multimeter, should conduct if good
- lecturer checks them via the solder pads, conducts like a fuse
- if it is failed, replace it with the same inductor

- tiny capacitors don't have numbers, how to replace them?
- pick the same shape and size
[can't you also measure capacitance of a good one?]
- or you can check the circuit diagram or schematic of the motherboard
the schematic will give the exact capacitor reference

the presenter has a printed book of schematic

- according to the lecturer, same size and color capacitors do have
the same characteristics, microfarads and voltage

- you can also look for another motherboard that is the same, and use
its capacitor

- but all ics and mosfets have a reference or characteristic written on them
- you can use an ic with the same characteristics, or an interchangeable one

- you can also pull out capacitors from differing motherboards that
have the same size and color

- connectors have references too

02-09 Cell phone motherboard connectors studying

- connectors are among the frequent repeated failures
- a battery connector, even if the pins are good, may be cracked
inside or a solder joint may have failed
- check the connectivity from the pins
- use the buzzer option of the multimeter
- check continuity from each pin to its solder pad
- the battery connector can be broken inside

- if the charge connector fails, check inside it
- the inside may appear in poor shape; replace the whole connector
- get another with the same size and characteristics; they are
different across models
- if inside the connector is good, check the solder connections,
signals and grounds both. the large connections to ground are not just
structural.
- shake the connector a little, see if it is secure
- you can resolder the pads if they are the only failure

- check the other connectors the same way, headphone, sim, switches, ...
- the sim connector and battery connector can break like the battery connector
- check each pin to its solder pad
- the sim connector may look like pins on one end connect to those on
the other but they are separate
- switches, either they are no longer functioning or their solder is bad

02-10 Cell phone motherboard Buses and tracking signals analysis

- traces on the board show connected pads and components; these are buses
- this is why shorted capacitors show a bad ic

- using this a schematic is not needed
- buses can be checked with a multimeter

02-11 Learn how to check and test motherboard components

...
- you can get an idea of what is a capacitor and what is an inductor
by seeing which ones, when not bad, short or not across them
...
the content seems to mostly be repeating

- careful when testing you do not touch your probes to other parts
...
- usually the failure is the IC rather than the capacitor, causing the short

02-12 Learn how to diagnose cell phone motherboard
1. visual inspection of all parts and components
- power jack, inside, solder joints
- battery connector
- sim card
- switches
- all the ICs; sometimes ICs are visibly burnt-out
- capacitors and inductors
- structure of the motherboard itself; is it broken?
- board connectors
2. check for 5V in power jack
- plug it in, ensure the adjacent capacitor has 5V
- if it is not 5V, the power jack is damaged
- the smd component may be on the backside
3. Check the ICs and chips
- check surrounding ceramic capacitors
- the IC pins may not be accessible, so we check the capacitors
- each capacitor should be grounded on only one terminal
- if both are grounded, the IC is bad
- ics have many terminals grounded with capacitors
- you can also check the ic with your finger, the heat of it
-  options: 1. feeling heat, 2. pvc capacitors around, 3. body of ic for damage
- example bad ic has burn hole in middle

02-13 Learn Cell Phone motherboard components symbols
- ceramic capacitor C: -||-
- polarized or chemical capacitor C,PC: -+||-, -+|(-
- diode D: -|>|-
- zener diode ZD: -|>Z-
- resistor R/PR: -/\/\-, -|=|-
- inductor L: -@@@-
- IC: rectangle
- crystal oscillator: -| rectangle |- x,y
ceramic capacitors around the IC grounding each signal pin are the
most important.

02-14 Conclusion
- learn laptop motherboard repair as cell phone motherboards are the same
- the big boxes are inductors
- you can also use a tablet motherboard
- try identifying processors, ICs, inductors, crystal oscillator
- learn the basics of laptop and tablet motherboard, then specialize
in cell phone motherboard. the ics are bigger.
- ICS have ceramic capacitors, mosfets, and inductors and maybe a
transistor around them. find these in every circuit group.
- after learning laptops and tablets, master the cell phone motherboard
- this gives strong understanding of the relation between chips and
circuits, and power management, say to random access memory
- try to begin with big motherboards on the laptop before going into
cellphone motherboards
- you can even do desktop motherboards