My GBA sp is using a 12mhz at the moment, anything higher than 15 and it won't work. CGB 24 and 12 both work fine. I'm pretty sure that palmertech said 69mhz was the fastest a GBA could take.

Sweet worked perfect for me. Gunna post a video in a minute.

Actually it works fine except it only works if I start it overclocked. If I try to switch it over while turned on it wont work. Though if I start it overclocked it will switch to normal?

Yep, that is normal.

If I wanted to be able to underclock it, would a 3.5 mhz crystal be good? I plan to use a switch that let me choose three different options (4 mhz, 8 mhz and 3.5 mhz)

I'd do 2mhz, because 3.5 won't make it slow enough, it will just slow it enough to mess with your timing.

Thanks for that pointer, should I use ebay to buy, or are there better sites? Sorry, I am very new to hacking in general... and I'm british =)

I use ebay and get 25+ crystals for cheap

Thanks for the help, I just have one more question.

Does the size matter in any way?

For example, there is a 8 Mhz crystal shaped like this:

And one shaped like this:

(I can only find the 2 Mhz crystal in the bigger shape...)

I'll leave you all alone now

Size really only matters if you're having troubles fitting it into the case There should be plenty of room though in the GBA.

Snip3rFire, I wouldn't recommend trying to use the larger kind of Crystal you linked to, which has 4 contacts on the bottom. I seem to remember reading somewhere that the ones with 4 leads on the bottom have some other circuitry inside so you can't use them the same way as the standard 2 lead types.

The "metal can" style crystals should only have 2 leads if you are going to use them to overclock a GBA. The surface mount crystal in the GBA has 4 contacts, but they are internally connected so that top contact on the right side is the same as the top contact on the left side (and the same for the bottom).

The small one would work fine. Just remember that if you want to underclock using a crystal less than the original 4.19MHz, you can not connect the new crystal in parallel with the original. You will need to remove the original crystal from the circuit board, and connect your crystals and switch directly to the board contacts.

Hey thanks a lot for this guide, I overclocked my GBA today with an 8 MHz crystal, it works perfectly.

I know that it doesn't work if you switch speeds while playing a game but I just had to try, I first fired it up at normal speed and switched the button, nothing happened, the game didn't screw up or anything so I could just play it at normal speed.
Then I started it up at fast speed, played a little while and listening to some in-game music (it was enjoyable) and then switched it to the normal speed while playing, the game started playing at the normal speed without having to turn it off, the game didn't screw up so I was pretty satisfied with the results.

It works from fast to normal but not from normal to fast.

the game was Mario & Luigi Superstar Saga in case you want to know.

after a while of playing on my overclocked GBA I found it a pity that I couldn't change the speed while playing, only from fast to slow and not the other way. Don't expect a real solution this!

I wasn't really looking for an answer I just got the idea when I was playing mother 1+2 and I thought: "Maybe if I change the speed to fast if the game is in sleep mode!?"

so thats what I did, turned my GBA to normal speed, launched the sleep mode and hit the switch.
... well, it kinda amazed me, the game played twice as fast as normal (its a succes), so it is a bit possible to change the game speed, if your game enables sleep mode, without having to shut down the system completely.

Although I didn't try with other games but I'm almost sure that will work on other games too.

It made my day.

Hey, sorry to bump a month old topic, but I had a thought about this issue with in-game speed switching.

What if there was a way to do it with a halt switch. I remember using one of those in my overclocked genesis to change speeds on the fly. You'd turn the game on with normal speed, flip the halt switch on, adjust the speed, then flip the halt switch off.

Perhaps there's a way...

I can't manage to do this mod. Tried for 2 hours. different clocks. I mean - i've got everything soldered(tried resoldering 4 times). I start it up, and hell naw, it won't overclock.