Sound cuts off, but if I touch the master volume contorl knob it comes on for a short time. Do I need a new knob, or something else?

Also how do I reconnect the fan?
It sounds like you may have a broken potentiometer (aka volume knob) for the master volume control. If that is the case, you would need to replace it with a new one (or take it to an electronics technician to diagnose and repair).
Regarding the fan disconnection, this likely isn't causing your issue but you would still want to reconnect it as it keeps your amplifier cool while in use. Reconnecting is fairly straightforward - all fans have 2 or 3 wires that connect to corresponding terminals on the amp. Just make sure you don't mix up which wire is positive and negative, and make sure they are connected firmly and securely.

I had this same problem. Pressing the panic button restored full volume, but again only for some seconds. I went to the 'midiscope' feature (in the global menu) to show any midi control messages that could be the cause. Indeed, it showed midi control message with volume, even though I did not touch any controls and no external midi devices were connnected. The midi scope in my case showed message was coming from midi channel 1, controller 11, which didn't mean much to me. I moved all knobs and sliders, like the pitch wheel and volume sliders and saw similar messages in the midiscope, but all on different controller numbers, not #11. Then I thought it could be coming from the external controller connectors on the back. I connected a foot pedal to them and found #11. With finding it, and by doing so, maybe cleaning or moving something in the plug connector, the problem disappeared and did never reapper.

This can be related to a fault in the potentiometer as it cut off the tracking of the voltage and gets back to feed the digital circuit. You need to check, sometimes a switch cleaning oil can help.
Try to wriggle the pot control many times as it can help, if not replace.

Sounds like it need a good clean.

Google a demo on how to clean the pots if you're not sure on how to do it!

Hope this helps!

If it happens every time you touch the timer knob, it does sound like the timer is at fault. Do you just barely turn the knob If so it does sound suspiciously that the timer is at fault. do you have to "push the timer IN?" to start it and restart it?

It sound like the master fader is faulty. Look here :-
http://stores.ebay.co.uk/methleykev

you can bypass the volume controller and use the master control. just take out the volume controller and splice the wires from there straight to master control.

It's not your ground wire with the issue, but your RCA cables. Try disconnecting both turntables, and connect 1 at a time, and do the same test, this way you can isolate the problem. Once you've isolated the problem, then you'll need to have the RCA cables replaced on your turntable.

You might also want to check the Cartridges as well. Sometimes a bad cartridge or headshell connection will cause this issue. Worst case scenario, its your tonearm, but that should be test last.

Also, on the rear of your mixer, there is a gain volume pot, make sure this is not maxed out. Keep it about 3/4 of they up. Again, this is on the rear of your mixer where you connect everything.

- OPTiC
http://djproaudio.com
http://djprolab.com

you probably have a lose connection. check all connections at both ends of the wires. if that dosen't solve the problem there is something wrong with the amp

Windows has a volume control built in, look at: control panel, sound and audio devices, volume control slider and check box for "place volume icon in task bar.