dreamcastfuse
Dreamcast Fuse
All controller ports are dead
If none of your Dreamcast controllers seem to be working, you've blown the fusible resistor, which is labelled "F1" on the circuit board. I haven't personally experienced the problem, but I've read about it quite a bit.
Can you solder? Do you have a friend who can solder? If so, it's an easy fix. You just solder in a new fuse.
The most obvious option is to buy another fusible resistor (also known as a "flameproof resistor"). The fusible resistor in the Dreamcast is rated at 0.39 Ohm ± 10%, 1/4 Watt. Don't use a standard resistor, they are not designed to act as fuses.
Another option is to solder in a fuse holder from Radio Shack so that you can easily replace the fuse if it ever blows again. The fuse should be fast-acting and rated less than 1 Ampere.
Personally, I'd install a "resettable fuse" instead. A resettable fuse automatically resets when you turn off the Dreamcast so you won't have to worry about a bad controller repeatedly blowing the fuse. You can get resettable fuses from electronic supply stores like Frys and DigiKey.com. I'm not sure what rating is correct, but Raychem Part No. RXE017 looks like a good lower bound. It trips at 0.34 Amperes.
Here are the instructions for opening up your Dreamcast and replacing the fuse:
http://www.forumplanet.com/planetdreamcast/topic.asp?fid=2387&tid=556026&p=1#4741117
Not recommended
The following is not recommended. If you can't wait another hour to play Space Channel 5, you can use pliers to twist the F1 fuse to short the two legs together. That'll "fix" your problem for now, but if you plug in a bad controller again, your Dreamcast will be unrepairably fried and could even catch on fire. As I said, not recommended.
Contradictions and Questions
Many other websites have instructions for performing this fix, but some of them are contradictory. Here are some random notes that may be of use for figuring out what is right.
Using a regular resistor is a bad idea, but better than just shorting the old fuse. If you go this route, don't take the advice of some of the sites to use a 10Ohm resistor. Too much resistance will limit the current to your controllers. You might not be able to use rumble paks or all four controllers.
What is the exact part that Sega used for the original fuse? People report that it looks like a blue resistor, but it has an odd five band color code: "Orange White Silver Silver Red". Some people have identified this as a "Pico Fuse", if that is correct, the fifth band (thick red) may designate that the fuse is fast-acting.
A sure way blow out the fuse is to plug in a controller with a short in it, and a good way to get a short is to have your cat chew on the controller cords.
Third-party controllers have been blamed for using too much current and blowing the fuse. Several web pages point to Performance brand controllers as being notorious. Others say that the fuse was rated too low to begin with and the allowed amperage should be increased.
One web site suggests using a 1/2 Watt fusible resistor instead of 1/4 Watt. While that's probably fine, I'd be hesitant to do it since it increases the amount of current allowed by an unknown amount. I prefer to know what I'm doing.
Someone (maybe me) should measure the current that passes through the fuse during normal operation. How many mA are needed to power four controllers, all of them with VMUs and rumble paks? What about with third party parts? Also, light guns, steering wheels, and fishing controllers probably require less current, but do they?