I'm making a portable Nintendo 64 (hence the title).

My questions:

1. How do I go about finding out which way I have to plug the batteries in?
Electricity flows from positive to negative in a battery... but how am I supposed to know if I hooked a battery up correctly, if I do wire it incorrectly (battery to n64 board) will anything burn out?

2. The little solder point thing on the N64 board has a "C" next to it (for composite video out). Isn't there supposed to be 2 connections when ever you are dealing with this stuff? (one for positive, one for negative).

3. Explain Ground to me (as far as this board having connections/pins for it goes).

4. Same thing as #3, except this is for audio.

The board has the L/R audio out pins, but doesn't it need a + and - wire for each?

 

Hi,
Sorry to say this, but if you have to ask that question, you probably shouldn't be trying to work on it yourself unless you don't care if you burn it up. Anyway, I'll help you as much as I can.

1) Yes, things can and probably will burn-up unless the original circuit designer put in reverse-polarity protection, which is highly unlikely in that kind of cost-sensitive consumer item. There are a few ways. But without seeing the unit, all I can offer are some generalizations. First, if it used batteries to begin with, instead of a power supply, it should be obvious which way they go in, just as in most battery-operated items. The "coil spring" end is the negative-side of the battery 99.9% of the time, and the "flat-blade" end is the positive. If it used a power supply only that plugged into a female connector on the unit, and you have the original power supply, then the power supply will specify whether or not the center pin is positive, etc. Beyond that, you must get a Digital Volt-Ohm-meter (DVM) and open the unit and apply a small DC voltage (perhaps from a worn-out AAA cell with a 100 ohm resistor in series while reading the voltage polarity on the DVM across the known power pins of an IC in the unit. As with most logic ICs, the power pin is the upper-right most pin with the notch facing up, and the ground pin is the lower-left most pin. So if you put your DVM (making sure to get the red lead in the meter's positive input) red lead on the IC's plus supply lead and the black meter lead on the IC's ground and you apply only a single 1.25VDC AAA cell thru a series 50 to 100 ohm resistor to the battery or power supply input and you get a positive reading on the DVM, then you have it polarized correctly. Now, you just need to get the correct voltage.

2) As for your composite video, again, not having seen it, I can't begin to answer that. Yes, any circuit needs a positive and a return (I don't like to use the term "ground" as it's misleading). Perhaps the return for the composite video is taken from the power supply input or some such thing.

3) Again, don't use the term "ground", use "return". Yes, your audio L & R need a return, but they may have designed that unit for the user to get the return from the power supply or from another connector. I can't tell without either seeing it or seeing a schematic of the circuit.

The return is likely the same for all of these; the power return, the composite video return, and the L & R audio return. Not to mention that most every IC or transistor circuit on the board likely has a common return connection. And although it's a bit unusual for audio and especially for video connectors not to have a return on their output connectors, as long as the return isn't too far away from the output connector (especially for video) then the return at anyplace on the board can be used, or a single return, being the battery or power supply minus connection, as they should all be common. Having said that, I cannot guarantee that they are all common as there are lots of ways to design circuits, some use split power supplies (like + & - 12VDC). The main thing is when probing your unit, to avoid damaging it, be cautious. Using a weak AAA 1.25 VDC cell with a 50 or 100 ohm series resistor will almost certainly not damage your unit (notice that I said almost certainly).
Feel free to ask me anything else if you have more questions.
Good luck.
Regards,
Kamran Kazem