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A Soldering Adventure

OP tablador

20th February 2012, 03:52 AM   |  #1  
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So I recently accomplished the unbrickable mod for the SGS4G and I wanted to provide some info and a story so that you guys can see what it takes to do the mod, and get some laughs about how badly I almost messed up my phone.

Here is the link to Adam's post, in case you haven't seen it.
http://forum.xda-developers.com/show....php?t=1333424

At the outset, you should know that I attempted this mod with the help of my friend, who has some experience soldering surface mount components, and has a rather nice temperature-controlled soldering iron, solder paste, clips, a flux pen, magnifying glasses, tweezers, and a jeweler's loupe. My point is that we went into this with a pretty decent set of tools.

Step 1: Na´vetÚ
After some careful thought, we attempted the mod and thought we had it. However, even with the loupe and other magnification equipment, we couldn't really see what was going on at these sizes. The phone booted, and I wasn't totally sure how the phone would behave unplugged. Plus we both had kinda run out of time for the day, so we called it tentatively good.

Step 2: Inspection
I happen to have a high megapixel camera with a macro lens, so later that day, I was able to get a suitable inspection picture and confirm that the mod did not take properly. It turns out that we had shorted the OM5 resistor, and this was causing the phone to operate normally, instead of being modded.



Step 3: Stupidity
Once I realized that the mod didn't take, I was disappointed and wanted to fix it. In my haste, I pulled out my RadioShack Cat No. 64-2067C soldering iron with the thought that I could maybe just touch the OM5 pad and get it to flow. Well, it turns out that cheap soldering irons are f-ing HOT and it immediately melted the adjacent resistor off its plastic(?) pad, which was now white. Oh, and the phone was now hard-bricked.



Step 4: Entropy
I called my friend for an emergency soldering operation. This time I brought my camera with me. We quickly cleaned off the solder. But now we had two effectively lifted resistors and decided we needed to come up with a recovery strategy. Based on looking at the pictures, we came up with a notional schematic. Unfortunately, in the process of probing with a multimeter to try to determine some resistance values, another resistor popped off. Well, damnit. We measured this resistor at 100k-ohms. So these look like protective resistors for what is probably a high-impedance input.



Step 5: Cleanup
We realized that the OM5 bridge was still there. This was based on a resistance measurement and you can see a bead of solder in the picture above which looks like it was still making a connection. We went in to try to get this solder to flow.



Step 6: Square One. Or Negative 2.
Things are getting bad. Two missing resistors, and our eyes are getting tired. Spouses are getting antsy. We decide the best way to move forward is to try to get a small bead of solder onto the tip of the iron, and try to create bridges where the resistors were. The first one was a success:



Step 7: Are You Kidding.
Well, with that rather clean-looking success, despite the fact that what happened above was largely due to good luck, we decided to keep going with this approach. We couldn't think of anything else to do... Unfortunately, we didn't know how to get a small enough blob of solder onto the gun, and the next blob was a little too big:



Step 8: Square Negative 3
What is immediately clear in the above picture is that we are completely screwed. Another resistor has lifted, and there is a sea of solder shorting the remaining resistors, and if you look closely, you can see two of the resistors floating together in the solder tsunami.

Step 9: Patience
We cleaned this up, and with some luck, were able to reestablish one of the connections. We still felt kind of lucky about that, and decided we needed to try another approach if we were going to proceed.



Here is an attempt at solder paste. Which basically was too messy to difficult to apply at this scale:



Also, notice the beads of solder in the solder paste. This is not normally what solder paste looks like to the naked eye.

Step 10: Slow Progress
We figured out we could reflow already-melted solder that was hanging around the station on some paper, and with some mushing and chopping motions with the iron tip on the paper, we could subdivide the solder into smaller and smaller quantities until we had a very tiny sliver floating on the end of the iron. We started doing this:



Step 11: Victory
Repeating this process with the solder beads bit by bit, we carefully added solder until we had the configuration we wanted. This was tricky, because surface tension wanted to keep the solder of the solder-resist. Also heat conduction would sometimes cause adjacent solder to flow when we didn't want to. First, we had this:



Yes, a mess. But we had determined through our schematic analysis that the left four resistors were originally grounded, so as long as we preserved a connection on the top middle resistor (above OM5) and prevented a solder bridge forming on OM5 itself, we were good to go. Now to work on the high pins:



Close....



Got it. This may look like a hot mess. And it is. However, notice that there is electrical separation between the logic level low inputs (connected by the upside-down L shaped glob on the left) and the logic level high inputs (connected by a glob which looks like maybe and Android robot doing a situp).

We booted the phone, and we had it. Successful mod.

Step 12: Denouement / Lessons Learned
  • To perform this mod successfully, you need to have access to good equipment. Visual inspection at these sizes is going to be difficult, especially if you start to get discoloration and other things making the image confusing to your brain.
  • Performing this modification requires a pretty high level of soldering expertise. These resistors are not much wider than a strand of copper speaker wire.
  • Have a way to verify your work. Like a camera, USB microscope, or some other way to get a good look at what you've done. Even with the loupe, this stuff was hard to see.
  • Be patient. Be aware of what surface tension is going to do, and what effect using flux will have. Practice on something if you have it.
  • If you are getting tired or fatigued, walk away for a minute and come back to it.
  • If you find yourself in crisis, think through the problem so you know how to define success.
  • Adam's guide in this forum is rather brief. However, he has references at the bottom that lead to quite a bit more information about what he has done. This information is valuable and can help you understand what is going on. I would review these references at least a little bit before you get started on this mod.
  • You can solder anything.
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20th February 2012, 03:58 AM   |  #2  
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Here is a picture to help with scale:

20th February 2012, 04:21 AM   |  #3  
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Wow the scale made it look a lot harder.

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20th February 2012, 04:28 AM   |  #4  
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Quite the adventure bro! I use a Hakko soldering station (var. temps). Works wonders. A little desoldering wire and flux are key. Glad you got it going! I've done the same thing in the past lol Literally a hot mess My only concern would be the 2 missing resistors. Good work. Thanks for the post!
Last edited by thegoo; 20th February 2012 at 04:39 AM.
20th February 2012, 04:50 AM   |  #5  
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Quote:
Originally Posted by thegoo

Quite the adventure bro! I use a Hakko soldering station (var. temps). Works wonders. A little desoldering wire and flux are key. Glad you got it going! I've done the same thing in the past lol Literally a hot mess My only concern would be the 2 missing resistors. Good work. Thanks for the post!

Yeah, my friend had a variable temp soldering iron too. We did a lot of the work at lower temps than usual in the hopes that the solder would be "stickier."

I was a little worried about the reistors too, and it may shorten battery life a bit, but there are probably resistors on the inside of the chip and they are likely high impedance (inputs usually are), so I doubt I will see a difference. On something like an ARM i would guess they would be rather high--i'm going to go ahead and guess 1M-ohm. I should look it up. Noise immunity should not be too much of an issue for configuration pins, and, well if a short develops inside the chip I suppose it could cause more damage than might normally happen but honestly if that were to happen the phone would probably be toast.
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photo essay, sgs4g, unbrickable mod
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