So, you've gone and blown your expensive CPDM (Core Power Distribution Module) by getting a battery plugged in backwards. Unless you're part of a really organized team, you probably have wires that have different polarities than the rest, or incorrectly wired batteries, or maybe you were just being careless, but now you've learnt your lesson. However, that doesn't help you now, you've got a 75$ brick and it's two weeks till your competition. What do you do?
You fix it yourself, of course!
Note: This will only fix CPDMs that have been blown by reversing the polarity of the battery. There is also possibility of burns and injuries when using soldering equipment. You are responsible for your own safety while following these instructions.
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Step 1: Stuff Needed:
So you're ready to fix it yourself? Hurrah! Let's get started!
Here's a list of things you'll need:
- At least 1 TPS5450 chip, you can get it here on eBay. (I bought two, which was a good idea, since I had to fix another CPDM later)
- A quality soldering iron or station. A used Weller station of eBay should do you proud. You could theoretically do it with a cheapo soldering iron, but I wouldn't try.
- Some flux. A flux pen works absolutely great. Here's a link to the one I have: SRA Flux pen
- Solder. Get some decent stuff, since you may use it again. Here's what I have: Kester Solder
- De-soldering wick. Here's what I've got: Chemtronics
- Some basic soldering knowledge. If you're a complete beginner, read this instructable through first.
If you don't have any of this stuff to begin with, I think you should go ahead and get it all. Here's why: Yes, it will cost about as much as just buying a new CPDM, but then you have everything you need to fix more in the future. Plus, you'll have soldering equipment, which really comes in handy. (And you should really have already anyways)
Step 2: Dissasemble the CPDM
Now you've got the stuff? Great! Let's take this thing apart!
There'll be 4 Phillips screws on the bottom of the case, simply pull the fuse, then remove the screws and the casing should come apart.
Step 3: Desolder the Chip...
Our problematic chip is the little 8 legged right behind the power switch. There are a few good methods of removing the it, and I'll go through them here.
Method 1: In this method, you basically coat all the pins on either side of the chip in a big blob of solder. Once the solder is all melted, you can push/lift the chip away. Here's an excellent video demonstrating this method.
Method 2: If you've got some small clippers, you can clip the legs off the chip, then desolder the legs from the metal contact pads the pins are soldered to.
Method 3: If you happen to have a really fancy soldering station with a hot air gun, you can use that to melt the solder on the pins, and just pick the chip up. This is probably the easiest method, but also, the most expensive.
Once you've decided on the best method for you, go ahead, but here are some things to be aware of: If your soldering iron has adjustable temperature, set it to about 315-350 degrees C. Be very careful with the other small components around the chip. You only want the chip gone, not these. One thing that helps with this is to have a small tip on your soldering iron. I did knock on off once, and was able to re-solder it, but it was a huge pain.
Step 4: Clean Up the Pads
We're going to clean the pads (Metal contacts on the board that the pins are soldered to) of the old extra solder, then apply flux so that the new solder will flow into place onto the pins of the new chip.
Take the end of your soldering wick, get a small bit of solder on your soldering iron, and press the soldering wick onto the pads with your iron. You should hear a fizzing noise as the flux evaporates and the solder is sucked into the wick. It should only take a few seconds. With the soldering iron on the wick, gently lift it off the pads- but be careful, don't lift if it gives you any resistance, because that's a good way to rip up a pad, and then it's pretty much irreparable. Repeat as much as needed until the pads look flat and clean of solder.
Once you've cleaned the pads, get your flux and apply a liberal amount to the pads. Don't overdo it, as you'll just end up with a lot of smoke and burnt flux, but don't underdo it either. If you get a bit too much, it's not a big deal.
Step 5: Prepare the Pads
We need some way to hold the chip in place while we're soldering it down. You could use tweezers, or a clamp, but an easy way is to tack the chip down in the corners with solder.
Take your soldering iron and get a little blob of solder on the end, not too much. Then, dab your iron to one of the corner pads where the chip will go. It should leave behind a little rounded blob of solder, which is exactly what we want. Do this on the opposite corner as well (Take a look at the picture to see what I mean). Now we're ready to place the chip!
Step 6: Place the Chip and Tacking It Down
It's a good idea to mark the polarity of the chip, or the way it goes, because if you get it wrong it'll just blow again. Taking a picture before you desolder the original chip is a good idea.
The end on your new chip with a line is the polarity. Match that to the notch in the white outline under the chip, IE, with the line facing away from the fuse socket. Make sure it's lined up well with the solder pads. Try to get it as close as is reasonably possible, but don't worry too much if it's not perfect.
Take your soldering iron, put a little solder on the end, and while holding the chip in place (You could use a pencil or some pointy implement), apply the tip to each of the pads/pins that we soldered beforehand, as seen in the picture. Make sure the solder flows around the pin and the pad to make a nice clean solder joint.
Step 7: Soldering the Chip
Now we're going to solder in the new chip we've tacked down. We're going to use a technique called "Drag Soldering". It's a very effective and easy way to solder surface mount chips with a soldering iron.
Take the soldering iron, and apply a small bit of solder on the tip to transfer heat. Touch the tip and the solder wire to the end two pins on one side, and make a small blob of solder there. Then, drag the iron (Don't press down, just drag lightly) across the remaining pins. Do this multiple times, adding more solder to the pins if needed. Once the pins are all coated nicely with solder, clean the iron and dab it on any solder bridges (Two pins that are connected between with solder) that happened while dragging the iron to remove them. If necessary, use the desoldering wick, but you may have to do the soldering over again because the wick can remove too much solder. Here's a nice video showing this technique in action.
Step 8: Cleanup, Reassembly, and Testing
Ok, I didn't actually do any cleanup around the chip when I was done.
Since there's probably a lot of flux residue, you might want to wipe that with some rubbing alcohol on a paper towel or a rag. I haven't tried this, but according to several videos I looked at while researching for this 'ible, it works.
Once you're satisfied with how clean it is, let it dry, then reassemble it. Simply put it back in the case, and screw the screws back in. A tip for starting screws that have just been set in plastic instead of a nice metal thread: Turn it like you're unscrewing it until it 'falls' a bit, then screw it in gently till it's tight.
Once that's done, plug it into a battery that works (And has the correct polarity), and see if it works!
If you have any questions, feel free to ask me! I try to answer them as best I can.