Fix Kindle Keyboard constantly freezing and rebooting

Foreword

The below information is simply my observations and opinions.  Should you try and make this repair yourself, try watching a few youtube videos on reflowing to get a good idea of what is going on.  You will void your warranty and have the potential of permanently damaging your Kindle.  So be warned.

In addition, this blog post is a bit rough in its formatting.  If you would like, there is prettier version of this in PDF form.  I wrote it for an English class and you may find it easier to read.  Just know that the temperatures for the reflow profile are only best guesses and were not actually tried.  It may take some trial on your part to get it right.

PDF

Background

My wife's Kindle Keyboard had developed this habit of locking up and requiring a reset quite often.  If you have a Kindle that locks up at random or stops working completely, you may have the same issue.

What I found is that the Kindle when working and sitting flat on a table, would work fine.  However, if it were picked up in a funny way or otherwise lightly twisted, it would lock up and require a hard reset.  As it turns out, the circuit board inside was flexing with the plastic casing and causing some of the solder joints to fatigue.  Eventually, some of the solder joints failed and cracked.  This is why when left undisturbed, it would work, and when picked up or handled, it would fail.

This post describes how to take apart, diagnose, and repair the Kindle by reflowing the damaged solder joints.  To do this, we will do something very similar to how the component was originally soldered.  That is, we will use a heat gun and heat up the component and circuit board to melt the solder and make a new solder joint.

You will need:
Heat gun
Tools for disassembly (set of small screwdrivers and something to pry the back off)
Tin foil
Liquid, no-clean flux (optional)

Disassemble the Kindle

To remove the back cover, you will need the wide flat blade screwdriver. There are locking tabs every inch along the edge of the cover with no screws to be removed. You can see how the tabs release here:

Next, you will need to remove the battery.  There are 2 screws and then the battery can be lifted near the screwed end and pulled out.  Make sure not to lose the 2 washers around the screw posts, these are not attached to anything.

Isolate the Damaged Component

The next thing we need to do, is verify which component has the damaged solder joint.  This will vary from kindle to kindle.  I will describe what I did and it may or may not help you.

Given how the Kindle froze and had to reset, I made an assumption that it had to do with the CPU or the RAM.  The EMI shield for the CPU and RAM is depicted below and can be removed by placing the corner of a flat-blade screwdriver in the corner of the shield and lifted.

I found it beneficial to use tin-snips or wire cutters to remove the bits of shielding that cover the CPU.  Since the Kindle would stop working correctly when flexed, I decided to press straight down on the CPU and memory to try and get it into a working state.  Once I did this, I reattached the battery by setting it in place and holding it.  I then waited for the Kindle to boot up and opened a book.  I turned a page and if it worked, I pressed lightly on the corner of the CPU or RAM.  I repeated this until I found which corner caused the Kindle to lock up.  I could then press on the opposite corner and it started working again after a reboot.  In my case, this proved there was a damaged solder joint under the RAM.

Prepare the Kindle for repair

Remove the battery.

Disconnect all connections.  Be careful with these connectors as they are a bit brittle.  Here are some images on how I removed some of the connectors:

Remove the 3G module if equipped.

Remove speaker connector.

Remove the screws.  There will be 8 black screws of the same size and 5 silver screws of varying size.

Remove the circuit board.  I found it easy to tip the circuit board to about 45 degrees by lifting the portion nearest the speakers upward and then pulling it straight out, away from the bottom of the Kindle casing.

Once the circuit board is free from the screen and casing, prepare the heat gun and your work area to heat the board.  If your work surface isn't heat resistant, you will want to place some non-flammable scrap between the circuit board and your work area.

Next, place the no-clean flux around the part to be repaired.  The goal is to allow the flux to melt and help clean the solder joints under the part being repaired.

You will also want to make sure you can hold the heat gun comfortably as the procedure can take several minutes.

The last thing to do, is use tin foil and mask off the area to be repaired.  At first, I used a small opening and only exposed the RAM chip.  I found this didn't work as well and opened the hole to expose the whole area inside the EMI shield.

Perform the repair

Again, the goal here is to mimic the temperatures originally used to solder this component onto the circuit board.  However, this is generally not a shared bit of information and some guesswork is involved in figuring out the correct times and temperatures.  What I did to try and get a feel for the magic temperature, was to use the heat gun on a simple capacitor and found at what heat setting the solder melted.  One thing to note, if you don't use enough heat, you can try again and use more.  But if you use too much heat, you give yourself another problem and potentially a nice paperweight.

I don't have exact temperatures used, but this is the heat gun I used and I found a setting of about 8.5 was good enough for the pre-heat and 9.2 was hot enough to reflow the parts under the component.

Generally, you will want to start with a slow pre-heating.  Again, I don't have exact numbers, but here is a general idea based off of general melting points of lead-free solder.  You will want to preheat the board to about 200-210C gradually over the course of about 5 minutes.  Once you have completed this, ramp up the temperature to about 230C and heat the component for about 30 seconds.  Once the 30 seconds are done, turn the heat back down to about 200C for about 30 seconds and gradually decrease the heat to about 100C or less over about 1 minute.  Then turn off the heat gun and let the board cool to near room temperature.

Once the board is cooled, place the circuit board back in the enclosure and connect all the connections.  Place the battery in last and see if it will boot up.  If it runs successfully, try gently pressing on the corners of the CPU and RAM to see if the problem is still present.  If the issue is still there, redo the whole procedure and use a higher heat setting.

If it works, put it all back together and give yourself a pat on the back.

New Kitchen Lighting

My wife and I moved in to a new apartment and with only work and no school keeping us busy over the summer, I took to projects to improve the apartment.  The first such project was the kitchen countertop where the lighting was poor and standing at the counter blocked whatever light might have reached it.

The solution to this was to make an LED strip to mount on the underside of the kitchen counter with a simple way of turning it on and off.  Of course we can't make it that easy, lets use a microcontroller.  I am using the PIC16F628A with a momentary push button.  I didn't have any D flip flops or other digital logic readily available and I have a small stock of these microcontrollers.  So we begin the development.

Code:

void main() {
TRISA = 0;
INTCON.B4 = 1;          //Enables the RB0/INT external interrupt
INTCON.B7 = 0;          //Global Interupt Enable bit | Disable all interrupts
OPTION_REG.B7 = 0;      //PORTB pull-ups are enabled by individual port latch values
OPTION_REG.B6 = 0;      //Interupt on falling edge of RB0/INT pin
PCON.B3 = 0;            //INTOSC 48 kHz

do{
PORTA = 0b00000000;
while(PORTB.B0 == 0);
INTCON.B1 = 0;          //Clear the interrupt so SLEEP will work.
asm SLEEP;
PORTA = 0b00000011;
while(PORTB.B0 == 0);
INTCON.B1 = 0;          //Clear the interrupt so SLEEP will work.
asm SLEEP;
}while(1);
}

Using a home built PIC programmer, I was able to download the code from MikroC to the controller and have it toggle the LEDs using the small, easily hidden push button.  The lever is so you can slide your finger along the bottom of the cabinet and hit the button without knowing exactly where it is.

These are the super bright white LEDs that I used for the project.

These LEDs are surface mount, but the width was just right for some speaker wire I had laying around.  I was able to scrape off the insulation and solder the LEDs directly to the wire.

From there, I used a simple transistor connected to the microcontroller to turn power on and off to the LED wires.

The final result of the project.  The LEDs were tacked with thumb tacks to the underside of the cabinet.