Replacing the LTSK (DC/DC converter) on your GP2X / Fixing the 'I wont work on batteries' problem'

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Introduction

First a small notice:

Disclaimer: I am not responsible for any damage, whether personal or otherwise. You and you alone are responsible. This is just a guide covering roughly how I did this but in more detail and with an introduction. I cannot be held accountable.

As many people still have a GP2X F100, and as it has several things going for it compared to the F200, I decided to write this article. A long time ago when I first got my GP2X F100 I didn't know much about electronics or etc.. One thing I also didn't know was how picky the GP2X is about it's power supply! When using batteries generally you can't do much harm. Getting batteries that are to strong is pretty hard and using those that have too low capacity will simply result in the GP2X crashing (and it is quite a power hog).

However you can also power your GP2X via an external adapter. Saves batteries (/charging time) and is safer when updating your GP2X. A win win situation you might think. Well it is really, however there are a few problems. First is that the GP2X's adapter socket is located a little annoying but more importantly the DC/DC converter used in the GP2X is DAMN picky. You need to make sure that the polarity is the proper way round (the other way round and your DC/DC converter is dead) and giving it (even slightly) more power then required and you fry it.

Just FYI, the proper polarity is center grounded giving 3.3V and around 1A.

Now as I used an El-Cheap-o-China multi-voltage adapter for my GP2X, which I set to 3.3V, it gave out a lot more then the 3.3V required. At first I didn't notice a thing, however after a while the screen started flickering and the GP2X failed to work on batteries. So I went over to my brothers laboratory power supply and started to test out how many Amps the GP2X was taking to boot up. Normally the F100 takes around 1A or less. Now it needed over 1.7A even to boot (I have to say I was happy that it booted all together)!

What part to get/replace:
After looking around I could only come to the conclusion that the LTSK (the DC/DC converter) was fried. Now I only know where the LTSK is on the F100. I don't even know if the F200 still uses this specific model DC/DC converter or if some other part is used. As for the location of the LTSK (and the orientation): the picture on the right is a picture of the PCB section underneath the yellow circle on the image on the left;

As you can see it is a small chip in MSOP packaging. Getting a replacement part can be a bit tricky. Looking just for LTSK on the internet might not get you the proper results. I've personally used the LTC3402 from Linear Technology as a replacement (no other parts needed). It works like a charm so if you need a replacement LTSK I can suggest you buy it (which I think you can from them directly). You can get the LTC3402EMS or the LTC3402EMS#PBF (the latter is the same as the first however it is lead free). Either will work (and I've tested both). At a price of 4.14 USD a piece I highly recommend you buy at the very least 2 when replacing the LTSK.

Opening

Once you receive your replacement part it's time to open your GP2X. If there is a system that is easy to open, it's the GP2X. Just remove the screws on the back and you're pretty much done. When you've removed the four screws on the back lift the back cover straight up (it might be held down a little by the battery contacts). I'm not sure if there were any clamps holding it together though, which shows that if they were there it still isn't hard to open it ;). Naturally when opening your GP2X keep all standard ESD safety guidelines. Make sure you're not static, not using any magnetic tools, etc.. Also I suggest you use a piece of (in case possible) anti static cloth/bag underneath the GP2X and place it screen faced down when opening.

Replacing the LTSK

After taking the PCB out of the plastic shell place it on an anti-static surface. Now find your LTSK. As you can see it is rather annoyingly placed in between other components and is relatively hard to reach. That together with it being small can make it tricky. However, being small also makes it easier to remove. At this point you do not need a small soldering tip yet. Having a bigger (though preferably flat like a screwdriver) soldering tip makes it easy to heat up all 5 legs.

Now many people will have a different way of removing the chip. General soldering experience and experience with small object soldering is VERY recommended. Not only for removing but also very much so for placing the new one. If you do not have experience take your GP2X to someone who has. And just to make sure, I am NOT responsible for whatever you do. You and you alone are (unless you take it to someone else).

Now to remove the LTSK I used an acto/stanly knife together with my big tipped soldering iron on the hottest setting. Naturally be very careful the knife, not only to avoid harm to the traces on the board but also to yourself. Another good tool to use is a pincer (especially one with L shaped legs you can use to get underneath the chip). I heated all 5 pins on one side and lifted that side. Then I let it cool down a little and heated the other side while pulling on the LTSK slightly. Remember when pulling on the chip to NEVER pull hard. You want to remove it from the pads. When heated properly it should come off easily, there should be NO need to pull hard. If you do you risk pulling the pads from the board. If you do, it isn't a big deal, you CAN use a wire to connect to the point where the trace leads in most cases (I had to as I pulled one pad from the board). If you do it is easier if you lift the leg up of the removed pad before installing the chip (i.e. \ \ \ / \ ) making it easier to connect a wire. Also pre-connecting the wire to the LTSK replacement might be easier.

When placing the new LTSK (LTC3402) I found it is the most easy to first add a slight bit of soldering tin to the pads of the board. Then if possible also add a little tin to the LTSK's legs. Now this isn't the best way of soldering something on but in this case it is the easiest and it will suffice. Then when you install the LTSK replacement (make sure you get the orientation right! Pin1 of the original LTSK matches with pin 1 of your replacement if you use the LTC3402!) simply hold it in place and, while using a small tipped soldering iron set to not too hot but hot enough, quickly touch the legs of the chip to make the soldering tins flow into each other. Preferably touch the connection between the leg and the pad to make both hot. Naturally do not keep your soldering iron on there too long in order not to damage the chip (or other components near it).

Now you should have a new LTSK soldered in. To test your newly fixed GP2X you can either put the outer shell back on, and insert the batteries. You can also use an external adapter (which you know works!!!!) or preferably a special power supply (laboratory power supply?).

It lives?

When you turn on your GP2X you should be greeted with the same screen you used to get before this whole mess. Now when I blew my LTSK the GP2X still ran from the power adapter (which gave out too much voltage) but the screen was flickering, that should now also be gone.

Anyway I hope you now have a proper working GP2X F100 again, and please, don't use that el-cheapo adapter ever again with your GP2X ;)!

-Simon van de Berg

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