Three hands. I was 'this' close to soldering it but it is just not working out. The solder is not bonding to the PDB and is not flowing I can't melt solder that I have already put on the wire . I am just going to get a more powerful soldering iron and try again. Meanwhile I mounted my ESCs to the frame using zip ties.

that's sad , but I use the same iron for any works.
well try with what you think is appropriate.

Thanks for all your help. I will give it another shot when I am fresh in the morning. Otherwise I will get a different iron or use a pre soldered PDB like the Hobbyking one

I tried again and following the tips from Sooraj, I got the PDB soldered  . While testing the setup, one motor was not spinning and would only pulse (spin once or twice) when I raised the throttle. I checked my PDB again and found a loose joint. After resoldering, during testing I appear to have destroyed one of the ESCs  . I am not completely sure how, though it could have been because of bad soldering or because I ran the motor at full RPM without a prop. Is there any way I can check the ESC or save it? I have decided to drop the PDB and use a wiring harness from quadkopters instead. I will need to order the harness and spare ESC and get back to this build. 

glad to here you did it .
there can be many issues for non spinning motor - it is not necessarily be bad soldering.
you can check this ESC and motor, by directly connecting the signal wire of ESC to throttle channel of receiver - the motor will respond to throttle stick movement, if ESC and motor are good.
There is no problem running a motor with out props on - it is always advised to tune and test your board only after all props unmounted.

one more thing, make sure you didn't reversed polarity of ESC power cables while soldering them to PDB.

I read on RCGroups that running the motor at full throttle without props can be harmful. I will try testing it how you described and get back to you.

Nope. One ESC is not working. It does not even power up the kk board or receiver when I connect. I will order a new one.

so it seams you burned it by soldering in reverse polarity - but as just a electronic circuit, I recommend you to rip off the heatshrink around ESC and look what is wrong in it (if you know what to do !!)

I have nothing to lose here  . I will check out the insides of the ESC.

I FIXED IT! The problem was so simple, I can hardly believe it. I removed the heat shrink and began checking continuity with my multimeter. There was no continuity between the positive input pad and the positive bullet connector! I cut off the connector, soldered a new one on, and the problem was fixed. Since I don't have 25 mm heat shrink, I wrapped the ESC in one layer of silver duct tape and put the original sticker back on  . Sooraj, your advice has been really helpful 

It's happy to hear everything is going fine
Wish you perfect landing .
Regards,
SPN

All systems are go!  Ground testing is complete. All the motors are spinning in the right direction. I can hear the motors speed up while tilting in self level mode. PI gains are on default as of now. I will maiden the quad soon. Any tips for mounting the props and battery and for the first flight?

you have KK 2 board I think is that right ?

for any flight - mount the props tightly, check the prop adapers have strong fit to motor shaft.
Battery should be mounted secure, It should not come of while quad tilts. (I did this wrong !).
everything should be tight and flight controller should be level.

which is your FC board ?

You are right. I have the kk 2.1(.5?) that came with this kit. I have calibrated the ESCs and the accelerometer. Receiver test is also done and I reversed the necessary channels. I am using a smaller battery for the maiden- a Wolfpack 2200mAh, attached with a velcro strap. Later on, I will use the larger Wild Scorpion 3500 mAh. Just have to double check everything before the flight. What happened to your quad? Did the battery fall off?

sorry - I found you have KK 2.1 , well calibrate accelerometers, by placing the quad in level surface.

check the receiver signals on FCB

now check minimum and max ranges of each channel as picked up by flight control board. min value should be -100 t -90 and max. value should be 90 to 100 for each channels. If not adjust in transmitter by decreasing end points.
trim the transmitter channels to zero in middle position (as seen on FC board)
check response to stick movements - the LCD will display the movement while moving the sticks. I mean when you move roll stick to left, the LCD displays left in side of appropriate channel.

sorry - couldn't read your replay while posting the above
my battery didn't come off but it hanged to  a side (deans connectors are strong !) , but that made lose of controll - but nothing worst happened as quad was in ground level

Wow that must have been scary  . Do you think the default PI values are OK:
P gain:250
P limit:100
I gain:250
I limit:20
Pitch and roll are linked. I will tune it later.

OMG ! - this is not default - better you noticed it- otherwise

Roll/pitch P-tuning:

Set the gains and limits to the following values:

Roll/Pitch P-gain: 30 (For a small 25cm size set to 20)
Roll/Pitch P-limit: 100
Roll/Pitch I-gain: 0
Roll/Pitch I-limit: 20

Yaw P-gain: 50
Yaw P-limit: 20
Yaw I-gain: 0
Yaw I-limit: 10

Now, Increase Roll/Pitch P-gain by 10 (5 or less for a small aircraft) at a time, and test your aircraft response by hovering and move the left stick in short and fast movements.
As you increase the gain you will notice:

1: The aircraft reacts faster and feels more connected to the stick movement and wander less on its own.
2: The aircraft may oscillate for a short time. Usually a few oscillations, but may be more if gain is high. If it oscillates continually the gain is too high.
3: The aircraft may be harder to land, it bounces back when touching down.
4: The aircraft may climb.

When the aircraft has a good response and does not oscillate or climb when testing, P-gain is good.


Roll/pitch I-tuning:

1: Trim it level.
2: Fly fast forward and center the stick.

If it level itself, increase I-gain.
If it stays in attitude, I-gain is good.

Alternatively setting I gain to 50-100% of P-gain does the trick.


Yaw P-tuning

Increase Yaw P-gain by 10 (5 or less for a small aircraft) at a time, and test your aircraft response by hovering and move the Yaw control stick until it have

yawed about a quarter of a circle, and then center it.

As you increase the gain you will notice:

Or just for a quick maiden, reset your board to get default values, - I still fly with default values - no problem so far

Thank you. Even I was wondering since they seemed very high. I am not sure why since I did a factory reset first. I followed the instructions in this video and changed the gains.

well if factory reset does not get these values as default, set it manualy and FLY!!
Default PI editor settings
Roll/Pitch Axis:
Pgain = 150
Plimit = 100
Igain = 50
Ilimit = 20
Yaw Axis:
Pgain = 150
Plimit = 20
Igain = 50
Ilimit = 10

I tried to take off but the quad is flipping. It appears that the back is too heavy. What do I need to do about this.

is the flipping happening with default PID

well I too had this flipping while take off - at first I thought it is a stick centering issue and compensated the flipping by stick movements while take off- but I was running old f/w at that time, yesterday flashed latest firmware- and now the quad is level in takeoff and there is a nice change in every attitude of it.

gonna upload video of my flights, stay tuned .