Where can I get schematic for the Gemini GX-450 powered speaker?

It will be difficult to get. If you wish to get some details; visit the site linked here. Pull up older posts. http://electronicshelponline.blogspot.com/ Circuit diagrams of many popular brand TVs and other devices are given. Search the site by entering the IC number used at the Gemini. You can get similar circuit diagrams there to refer, i think.

I have the GX Gaming speakers and occasionally the power will not come on when turning the knob. Unplugging the power cord for 30 seconds or so fixes the problem. Only unplugging for 10 seconds is not sufficient.

There are several possible solutions for this. The cheapest and easiest is to do the following:
Solution 1:
1. Get an RCA stereo plug to 3.5 mm plug. This will go from your mixer to your computer. This will not be the highest quality, but will work.
2. Get an XLR cable of the length you need. I would guess a standard one with a male connection on one end and a female on the other. Connect this to your powered speaker. Also, this is a guess as you didn't include the type of powered speaker, so I can't tell you for sure which cable to use.
Solution 2:
1. An alternate idea for better sound quality would be to run a D/A converter similar to this one: http://www.sweetwater.com/store/detail/USBMix/It would give you a much higher sound quality for everything. You would run from your Gemini to this. From this device, you would run a USB cable to your computer, and a 1/4" cable to your powered speaker.

typically (unless your useing other gear besides mixer and amp) you'd come out of the L/R outs. ( Main outs ) to the Main inputs of the power amp then out to your speakers (outs of power amp). Now the amp could be in bridge mono or other factors but typically, like i said, just
Mixer Out- Amp In- Amp Out- Speakers.

Don't even think of using a universal adapter !!! I could not find the schematic of this unit, but other Gemini mixers like this use center tapped AC power transformers. Any universal adapter will be DC, not AC. I have found that the FX7000 indeed uses an 18 VAC adapter... Try this as a source:

http://www.topdjgear.com/gemini-110vac18v.html

A large amp like this likely has protection circuit (probably a relay) that doesn't connect the speakers until the amp is stable and balanced. You relly need the schematics for the amp.

It may NOT have a fuse. If too much power was sent or an amplifier drove DC to the speaker, the voice coil may have fried. The specs do NOT brag aboput protection, so it is likely either the speaker is blown or the internal wiring is broken. Open the unit and use an ophmmeter to tesst the speakers.

You connect POWERED speakers to the left and right outputs... You MUST use POWERED speakers or an external amplifier. This unit has a small headphone amp, but that CANNOT power passive speakers.

My computer no sound driver

the gemini p-601 is not bridgeable. you can select either speaker pair a, speaker pair b, or both pairs, but you can not bridge it without potentially damaging the unit.