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Serviceman's Log

Un-bricking a Samsung smartphone

by the Serviceman

Items Covered This Month

• Un-bricking a Samsung Galaxy smartphone

• The iPhone that swam in Coca-Cola

• False-alarming security system

• Resurrecting an ancient Fender Champ guitar amplifier

*Dave Thompson, runs PC Anytime in Christchurch, NZ.

Regular readers will know that I’ve spent the last few months doing battle (off and on) with a “bricked” Samsung Galaxy smartphone (ie, a phone that had been rendered useless by a software update that went horribly wrong). And when I say “doing battle”, that’s exactly what I mean because numerous attempts at un-bricking what had become an expensive paperweight had left me with egg all over my face.

Of course, I really only had myself to blame. After all, I was the smart-alec who had bricked the phone in the first place!

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Those with total recall will remember that my main challenge in resurrecting this unit was how to connect a programming box of tricks I’d purchased for the very purpose. Once I’d achieved that, I would then be able to flash enough data into the phone’s ROM to get it to boot into a state I could do something with; or at least, that was the theory. In the vernacular of phone-geeks, I would be able to “un-brick” it.

The good news was that Samsung made provision for just such a connection. The bad news was that this-so-called “JTAG” point consisted of a series of DIL pads designed for a tiny 12-pin header connector, which was not included. With a pin pitch of just 0.4mm, each row of six pads covered just 2mm on the board, making it smaller than anything I’d ever worked on before.

In fact, I could barely even see the pads let alone connect wires to them. This is where my illuminated magnifying headset really came into its own; without something like this, working on such small components would be impossible.

In order to make the necessary connections, a friend and I had brainstormed the design of some programming adaptor jigs. He was going to turn them out on his laser-engraving machine. The problem was getting the laser fine-tuned enough to drill two rows of holes just 0.15mm in diameter but it turned out that the laser could do that standing on its head.

Our idea was to make a jig from some clear acetate sheet, shaped like a butterfly. Rows of holes in the centre of the jig would match the DIL pad pattern in the phone and I could then thread 0.13mm wires through these holes and run them off to larger pads spaced far enough apart in the “wings”. I would then be able to easily solder heavier wires to these thin wires and run them to my JTAG programmer.

After that, it would simply be a matter of clamping the jig onto the pads and the wires would make the necessary contacts.

Well, it all sounded fine in theory but when the jigs arrived and I saw how tiny everything was, I began to have serious doubts. I had to try though so I stripped the insulation from some multi-core hobby wire and used the individual 0.13mm strands from that to thread my jig. It was all a bit fiddly but with the aid of my magnifying headset and a pair of needle-point tweezers, I soon had each row of six holes wired up.

However, I had to be careful not to pull the strands too tight for a couple of reasons. First, the wire was very fragile and easily broken and second, too much tension pulled the tiny jig out of shape.

When I finally had the jig wired, I tried to fit it onto the pads. But while I could position it correctly, it would immediately twist off to one side or the other each time I tried to clamp it.

After several abortive attempts, it quickly became obvious that this was just not going to work. The theory was good but in practice it just didn’t work out.

Click for larger image

At this point, I was so disappointed and frustrated that I was ready to chuck it in and put it down to experience. But the fact that others were doing this successfully to the same phone drove me to look once again at sourcing the headers the circuit board was designed for. If you recall, I had gone down this road before only to find that they were not available in New Zealand. And all the companies that sold them online wanted a minimum of $US30-50 to ship one to me.

You could fit 30 of these headers in a matchbox, so charging that much for shipping was just a rip-off. Most of these companies also had a minimum spend of $30 and given that the parts I wanted were just 89 cents apiece, I’d need to buy quite a few of them plus a lot of stuff I didn’t really need just to reach that dollar value.

As a result, I emailed every vendor I could find advertising either these Molex or Panasonic headers and asked them to make an exception to their minimum order and/or minimum shipping costs. Not one of them would budge so I got nowhere and on principle, I will now never buy anything from any of them in my lifetime.

However, one company did at least apologise and advised me to contact an Auckland-based company that may be able help. I contacted them and to my delight discovered that they could supply the Panasonic male and female headers I needed and would only charge a few dollars for shipping. I would still need to spend at least NZ$30.00 but I considered this to be a reasonable compromise.

I purchased several of these male and female connectors in case I made a mess of things and while there, ordered some surface-mount solder compound. I have almost zero surface-mount soldering experience, other than tackling the odd suspect dry-joint, so the thought of soldering these connectors in place was giving me sleepless nights. I searched the web and read up all I could about the subject and figured that with the right soldering tools and this recommended soldering compound, I should be OK.

Cold feet

The package arrived a few days later and when I saw the headers in the flesh, I got cold feet again. They were even smaller than I had imagined. However, the flux compound had excellent instructions on how to use it so I told myself I could do it and set about getting everything prepared.

First, I cleaned the circuit board and pads with isopropyl alcohol and applied a microscopic amount of the flux, which comes in a syringe, onto each pad (or as close as I could get to them). I then orientated and placed the header connector using a pair of tweez­ers, pressing it as tightly as I could onto the pads. After then nudging it into place with the tweezers, I took a deep breath, cleaned and tinned my smallest soldering-tip and touched the corner pin. Solder instantly flowed into and welded nearby pins to their pads underneath. I could scarcely believe it.

A few touches of the soldering iron tip to the remaining pins had the header soldered beautifully. I checked out my work with my high-magnification jeweller’s loupe and it looked perfect, with no bridges or dodgy-looking joints. I readily admit that it had nothing to do with any great skill on my part; it was all due to that solder flux.

It certainly cured my previous reluctance to work with surface mount technology on future projects.

But having the header connected to the board was only a third of the battle won. I still had the problem of connecting my JTAG programmer to it. I would have to use the matching female header for that and that would have to be soldered to a board of some kind which would then connect to the programmer.

During my internet travels I remembered a guy who had built his own expansion boards and I figured I’d have to make something similar. The board I’d need would look like a spider, with the pads for the header being the body of the spider and “legs” leading from each pad to larger solder pads for heavier-gauge expansion wires.

I’ve made hundreds of boards before but nothing on this minute scale. I doubted that my laser printer could even print a 0.125mm line and even if it could, there was the question of whether my basic photo-etching set-up would be capable of producing the board. There was only one way to find out and that was to try.

I use DipTrace to draw schematics and design circuit boards. I fired it up, found the pads to suit in the software’s pattern library and set about designing the board. It all looked easy as I zoomed the pattern size up on my 24-inch widescreen monitor.

Once I had the DIL pattern in place, I created 12 normally-sized pads to solder the programmer’s wires to and ran the various traces between. However, when I shrank it down to normal size, it just looked like a blob in the middle of my screen with no discernible features. However, I went ahead and printed it out actual size and it actually looked great, with clearly-defined traces, pads and holes. At least the printer was up to the job!

I then printed it out on the clear acetate sheet I usually use for making PCBs and it too looked good. I use Kinsten-brand materials for making all my circuit boards so I found a tiny off-cut, lined up the acetate and exposed it in my lightbox. I then developed it carefully using a weaker-than-usual solution of developer and etched it in my tank.

The resulting board measured just 9 x 10mm and it looked perfect. Nevertheless, I used a multimeter to check that each header pad connected to its corresponding expansion pad and that there were no bridges between the pads.

That done, I carefully soldered the female header onto my expansion board, using the same technique described above, and this too was successful. I then soldered the programmer’s leads to the relevant expansion pads.

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