Precautions to ensure
that your KeyMaker 9A USB and ThinkPad are not damaged
In order to avoid damage to your KM9AUSB
board there are certain precautions you MUST observe.
Your KM9AUSB has electrical contacts on
both sides, you must ensure that no part of your KeyMaker USB board
comes into contact with any conductive surfaces such as bare metal or
You should place down a piece of paper
and place your KM9AUSB board on top of it in order to avoid any
electrical contact which may damage your KeyMaker.
There is no danger of receiving an
electrical shock from your KM9AUSB as the highest voltage anywhere on
the board is 5 Volts which is a safe voltage to touch.
If you like you can place your KM9AUSB
board inside a plastic bag during use, the board does not get warm
at all, so there is no issue with ventilation.
The same precautions apply to your
ThinkPad when you are performing any operation and your ThinkPad is
switched on, you must ensure that nothing can short out by coming into
contact with other parts, you can use sheets of plastic or plain paper
to make sure things remain electrically isolated.
The 4 leads from the KM9AUSB I2C
connector are VCC, GND, SCL and SDA.
GND is connected back to GND on your mini
USB connector and onto your PC or laptop.
VCC is connected to the 5V DC supply from
your USB connection, it then passes through a self resting Pico fuse, so
it is well protected should you accidentally short it out, in 99% of use
we do not use the VCC lead anyway.
You do need to take care with the SDA
and SCL leads as they are NOT protected.
If you are careful and NEVER connect SDA
or SCL to anything other than the SDA and SCL pins of an EEPROM no
damage will ever occur.
However if you accidentally make a
mistake and connect either SDA or SCL to GND or VCC on your KeyMaker
Board or inside your ThinkPad you will damage the KeyMaker USB SDA and
or SCL I/O pins.
The reason is that the SDA and SCL I/O
pins connect directly to pins on the Microprocessor on your KeyMaker
The SDA and SCL I/O pins MAXIMUM DC
Current from either the SDA or SCL pin is 40 mA, that is 40 thousands of
an Ampere, a VERY small amount of current.
If you exceed 40 mA you will damage the
I/O pin and your KeyMaker will not function.
You will exceed 40 mA if you directly
connect SDA or SCL to either GND or VCC anywhere on your KeyMaker USB
board or inside your ThinkPad.
Therefore you must double check that you
do indeed have the correct lead and you are about to connect it to the
correct point BEFORE you actually connect it.
If you want the luxury of being
careless, make serious mistakes connecting to an EEPROM and not cause
damage, there is a way you can protect your SDA and SCL I/O pins so that
they cannot be damaged even if you accidentally connect either to VCC or
The protection consists of 2 x 180 Ohm
resistors. Very inexpensive insurance.
One 180 Ohm resistor is connected in
series with the SDA lead.
Another 180 Ohm resistor is connected in
series with the SCL lead.
Below are photos of how I modified my 4
way I2C lead to make it safe against accidental contact with GND or VCC
I make no warranty that any of my
information is correct, or safe, or does or does not breach any warranty
clause, or anything else, it is up to you to decide if you will
follow all or any of the instructions to recover the Supervisor Password
from a TP. It is up to you to decide, I am not responsible for the
results or for any consequential or incidental damages whatsoever.