Rossmann Repair
Training Guide
Created by Louis Rossmann - Open-sourced to the internet (that’s us!)
https://www.youtube.com/user/rossmanngroup/
You can read more about our company here & inquire about service. https://www.rossmanngroup.com��We have a paid forum to provide support to component level technicians https://www.rossmanngroup.com/boards��We offer training at our store https://www.rossmanngroup.com/logic-board-repair-training-class/
The biggest problem in this business
You do NOT need to be an engineer!
expert on physics, chemistry, and electricity.
Electricity is based on theft and burden
you by causing a pain point.
Electricity works the same way
To get electricity to do anything, we manipulate it
within a no-fix-no-pay business model?
This is what we are doing to electricity
this path, you'll get what you want.
Just as the elephant walks to get the peanut,
Electricity goes through anything to get to ground
QUICK QUESTION: HOW MANY VOLTS ARE AT EACH POINT IN THIS CIRCUIT? Answered at next page.
If 120v is applied to the lightbulb but there is no “path to ground”, it won’t light
Just as the elephant has no motivation to get up off his ass without the peanut being dangled, a p won’t cause electrons to flow without a complete circuit. Just because we apply 120v to the light bulb does not mean it will turn on if we do not complete the circuit by adding a ground on the other end.
How do we measure this?
Ohm's law helps you figure this out
Your 4th grade teacher told you “you won't be carrying around
a calculator everywhere for the rest of your life”
How does this work?
TO KEEP IT SIMPLE:
Try not to just not remember it like a sheep would, try to understand it like a good student would! If you understand, you do not need to remember.
Just learn that in a Fraction:
A / B
B is the denominator and A is the numerator, When A is higher than B, a value higher than 1 will be the result of the fraction, and when A is less than B, a value lower than 1 will be the result.
Example : A=50 B=10 -> A/B= 5
A=50 B=70 -> A/B=~0.77
5>0.7
Remember the formula in the previous slide:
P=V^2/R
Remember the formula in the previous slide:
V=R x I
This is simple... higher are the terms in the product higher will be the result
Example from a speaker amplifier, the Rotel RB-1090
Lower resistance = more power! The same amplifier can put out almost twice as much power when a lower impedance speaker is attached.
You do not SET current!
Let’s check out a real world example
Now you do it!
Answers!
AC is Alternating Current
It alternates between positive and negative. So, it's called alternating.. get it? Up down up down.
DC is Direct Current
DC doesn't move back and forth, it is a straight line.
Direct - straight - get it?
This is also DC but a crappy one
The more straight the line the better
*(We use capacitors to make it as straight as possible)
Laptops use DC
Getting a computer processor to work using AC would be like trying to play Jenga on a roller coaster. We do not use AC for powering most parts of laptop and cellphone circuits. We want flat, steady voltage.
Think of ground as a black hole
This is the symbol for ground
Resistors resist the flow of current
You typically have the same or near identical voltage on both sides of a resistor, but less current flows (Note from Paul, this slide is 100% wrong and needs to be corrected, pay no attention to this slide)
near 0V drop
This is the symbol for a resistor
How resistors often fail
Capacitors consist of two charged plates with an insulator sitting between them
How capacitors often fail
Cool things we can do with a capacitor
Knowing that we LOVE using Capacitors to smooth out signals!
What is a short circuit?
Example of a working circuit
Example of a short to ground.
before power can flow
“TO SYSTEM”
Finding a short
We have five happy caps on this line. The line works great!
Until one day, water is spilled, and a cap explodes. C7544 is now sending all the voltage to ground!
Measure each cap, right?
Go back to the light bulb example: do brighter bulbs make more heat?
We can use heat for short detection.
What is an inductor?
This is the symbol for an inductor
What is a transistor?
TO KEEP IT SIMPLE:
A transistor is a resistor whose value can change.
If you're an electronics engineering major, yes, they are not linear devices, kindly STFU. We know.
from source to drain dependent on the voltage at the gate.
Types of transistors we care about
What voltage is present on the drain when 12v is on the source and the gate of this MOSFET?
0 volts! A P type MOSFET opens when voltage on the gate is lower than what is present on the source. Schematic claims 4.5v, but there is always 5v there in the real world (SCHEMATICS ARE NOT ALWAYS RIGHT)
HINT!!!! Ground = zero volts!!
It lets power through! N channel MOSFETs let power through when the gate voltage is higher than the source. Ground is 0 volts. If there is 3 volts on the gate then it will open. This will then send whatever is on the drain to ground, which will cause 0v to be on the drain.
What is a voltage divider?
Here we have a resistor between a high voltage source and the intended destination, then another resistor between the intended destination and ground. It is turning 12v into 4v.
Reminder: what is a voltage divider?
What if we used a transistor to control the voltage dividers path to ground?
control backlight being on or off based on signals from
other parts of the machine.
What is a pullup resistor?
of providing amperage for on a given data line.
What happens when creating a data line without a resistor to limit current. Remember, the chips are shorting the signal to GROUND down to ZERO VOLTS to make this work.
THAT IS WHY WE USE PULLUP RESISTORS!!!
What is a Diode?
This is the symbol for a zener diode
What is a voltage divider?
have high current requirements.
Here we have a resistor between a high voltage source and the intended destination, then another resistor between the intended destination and ground. It is turning 12v into 3v.
NOW ONTO THE FUN!!!!
we can go on to basic circuits.
What is a data line?
Here is the battery, battery controller IC, and SMC speaking to one another.
Creating a data line
A resistor is placed between a DC voltage line
and the data line to create the data line
Here is the 3.42v side of the pullup resistor. Look, plain flat 3.42v of DC.
This is the DATA side of the data line. Note how the chip is creating data by making voids in the 3.42v of different width and height. This means something
DON'T ASK ME!!!!
documented there’s usually enough information to infer what is
supposed to be happening in optimal circumstances -k
What are we interested in when checking data lines?
present on the data line?
When troubleshooting a data line running on a 3.42v power line...
What is a power rail?
can attach components.
Here a resistor, capacitor, and inductor are attached to a 5 volt power rail.
If a power rail is **MISSING**
to figure it out.
How circuits fail
s pulling all the power to ground when it should not.
Checking for shorts to ground
believe is not working how it should.
Finding a short to ground on the line.
Other benefits of diode mode troubleshooting
For example, on backlight circuit output on LP8550 based boards....
LED driver
LED driver.
These numbers do not come from thin air!
to the issue in my brain.
mode measurement. Without wasting brain power
checked what was wrong the last time I had that number.
You can use this to make your own “ANSWER KEY” when you are lost!
The possibilities are endless - build your own answer key using diode mode measurements so you do not have to reinvent the
wheel every time a board has a problem.
What are power STATES?
need CPU vcore during S0 while it is on, but you do not want
it when it is off – S5.
When troubleshooting power rails, is the rail ABOVE the rail you are troubleshooting working?
When troubleshooting power rails, is it even being told to turn on?
50 resistors/capacitors?
How many people get sick looking at this?
Let's make this simple. First; is it being told to turn on?
See how we ignore all the shit on that page that is boring to get to what is relevant?��P5VS3_EN_L tells Q7221 to short the ENTRIP pin to ground. According to the datasheet for TPS51125, the chip will NOT create a 5 volt power rail while its entrip pin is shorted to ground! We need to get rid of this terrible P5VS3_EN_L signal. ��Let's follow further down.
P5VS3_EN_L is shorted to ground if PM_SLP_S4_L is high
PM_SLP_S4_L is where this ends
the enable signal getting fucked up somewhere else in the line?
The problem is often that we running down the wrong hole;
one within which a rabbit does not even reside.
What is an integrated circuit?
Here is an integrated circuit
WTF is this?
A few basic things to take note of
VCC, VDD, VEE, VSS, or VIN.
YOU WANT 5 VOLTS TO BE THERE!!!
What is a logic gate?
What is a buck converter?
lower voltage.
We start with a high voltage, like 8 volts
Buck converter “switches” it on and off. 8 volts, 0 volts. 8 volts, 0 volts. This sucks. Would you want to drive in this car???
Output is “averaged” to 0.8 volts by an inductor�and a capacitor into a nice flat line. Ahh, much nicer ride, says the CPU.
What is a DC to DC boost circuit?
moving forward faster than the speed of the car. Good thing
we have seatbelts!
Same concept is applied in electronics.
A laptop LCD backlight runs off of about 39 volts in an A1286 Macbook Pro.
Its BATTERY is a 12.6 volt battery. Does this mean we carry around flashlights?
NO!!! We boost it.
line.
DC to DC boost circuit contains four main elements
Unboosted 8 volts. BEFORE INDUCTOR!!!
Voltage after inductor when switching to ground
Voltage after diode & smoothing capacitors
What is current sensing?
is using.
If a circuit is using too much current, current sensing turns it off.
Common faults
green light, quarter fan spin.
is exploding it will turn off charging.
What is the onewire circuit?
the SMC.
QUICK REFRESHER: Remember what a logic gate is?
The 3.42v that comes out of the LAST chip powers this chip that sends charger data to the SMC.
SMC_BC_ACOK can be brought low by the U7000 - which controls creating the main 12.6v rail of the machine from the charger power.
This can stop the onewire circuit from allowing the charger voltage through to the machine.
So the way this works...
U6901 is a logic gate that will let PP3V42_G3H(3.42v) through to U6900 ONLY if SMC_BC_ACOK is present. U690 allows communication between the chargers adapter sense line and SYS_ONEWIRE which goes to the SMC. This is how the SMC talks to the charger. The SMC tells the charger things like “TURN ON!”, “TURN ON BUT LIMIT POWER!”, or “DON'T TURN ON!” Without this data line being present, the charger will NOT TURN ON!!
PP3V42_G3H needs to turn on first.
**BEFORE**ANYTHING**ELSE** !!!!!!!!
If you have a green or orange light on your charger; PP3V42_G3H works.
Is the SMC on? How do we tell?
How SMC communicates with ISL6259
What turns the SMC off?
Let's move onto PPBUS_G3H
After this, the rest is dependent on your specific system
PCH
These signals differ from platform to platform
The BEST way to figure this out if you are unsure...
What is FEEDBACK and why does it matter?
are doing.
Standard backlight circuit faults!
Hey, I have no backlight... right?
WTF is a DDC circuit?
Make sure you check that you have an image.
Is the computer's “brain” even turning on?
or MCP vcore, or power going to RAM, then the issue is not “no image” - it is “NO BRAIN!!!”
If all voltage rails are present and it doesn't
do anything...
working.
If CPU voltage rails are missing...
IC is NOT BEING TOLD WHAT TO DO!!
I fixed it and they say it runs slow
itself from damage.
Run ASD to tell you what sensor is failing
to check the schematic and see what's going on.
PBUS voltage sense, VP0R example
Types of sensor failures
Sometimes the data line on which the sensor is communicating is being brought down by something - dirt in a webcam connector, a bad webcam, a bad chip. Check if the line is topping out at the max spec'd voltage of that data line.
i2c
i2c is one of the primary interchip communication busses
Shown as SDA and SCL on schematics and datasheets.
SDA - Data Line : SCL - Clock Line
Both lines will have a pullup resistor to a power rail - If the pullup is open, short, or out of spec i2c will not work properly
Its purpose is to provide communication/instruction to an IC. That is to say, even with power, ground, and enable, many ICs need programming over i2c to function.
The entire i2c bus can monitored and communicated with via inexpensive external tools with a connection to SDA, SCL, and GND
Basic functionality can be determined with DMM and Oscope. You won't know what the bits mean but you will know they are there.
How Apple plays dirty with LCD’s
Unlike any other manufacturer, Apple includes a special validation/genuine string in the LCD EDID Block.
Before any power or data is sent to the LCD this must be validated via the DDC handshake.
In the event of liquid damage where your EDID data may get corrupted, an otherwise functional LCD will not turn on when this validation fails.
EDID data can be read, verified, and reprogrammed with inexpensive tools (Bus Pirate, or literally any other i2c programmer). It is a simple 2 wire i2c EEPROM
If backlight voltage gets sent to your EDID IC you can pretty much guarantee it will be corrupted.
Valid data can be pulled from the same model Macbook and programmed to the damaged lcd without issue.
How to get 20V on USB-C powered machines
What is this CD321X BS and how do they work?