There's a button on the back of my vlz pro that says main output +4...if the button is depressed it pads the unit..i saw that in the manual. my question is, for live performance when i use the mixer to drive my powered speakers..should i have the button pushed in or not?? thanks.

Just worked on one of these. What causes this is when one of the 16 volt plus or minus supplies is shorted out or low. Check the supply voltage and PRAY that the fault is NOT on the main board... takes a lot of time to pull all the knobs and unscrew the main board and the headphone jack to get the board out. The one I fixed had the MAIN insert driver blown causing no main output. Here is your service schematics... note there are SLIGHT discrepancies depending on the vintage of your unit.:
http://elektrotanya.com/mackie_1604vlz.pdf/download.html

Scroll down to "get manual" and click to download. IGNORE other download links.
You can access the power cable to the main board by removing the bottom access panel. You will find the voltages reading across the connector from left end as +16, grd,-16 and then several others including one at about 9.5 volts and then the phantom power at around +48 volts... You may find the -16 or +16 pulled to the opposite polarity if one of the regulators has failed. This supply runs very hot and seems to be enclosed in a mu-metal magnetic shield as well... or at least the one I repaired had that.

Use the main left and right... the CR outputs are INTENDED for running control room monitors.

Transformers are VERY reliable. Look for another problem... rectifier, filter caps, fuses, regulators. There is a main fuse and if it is blown, repair the unit before applying full power. To test the unit, put a 40 watt light bulb in series with the hot side of the power cord. The light will act as a resetable fuse and will light when there is a short within the mixer, thus absorbing most of the voltage. Enough current will flow to diagnose the problem.

With LED intensity changing with operations, that MIGHT be a symptom of the power supply going into current limiting mode.

The first thing I would do is to check the power supply voltages with an oscilloscope to assure that the voltages are stable and not dipping...

Now from my experience when I hear that a transformer had to be replaced that means it suffered over voltage or under frequency. I would IMMEDIATELY suspect that one or more of the rectifier diodes might be open. With only half wave into the caps the voltage will dip below what the regulators can handle giving weird effects. Check the +/- 16 volts with a scope that they are PURE DC and don't have ripple due to either damaged diodes or C6 or C7 being degraded. I assume you have a schematic... if you don't here is a link:

http://elektrotanya.com/mackie_1604-vlz-pro_mixer.pdf/download.html

The best way is to use a two-way crossover between the mixer and the amplifiers. In your case, the low output from teh crossover would go to the powered subs, the highs to the QSC. Use the crossover adjustment to set the frequency crossover point to get the sound quality you require.

Dan

Mackie 1604 ---> Crossover --- Highs ---> QSC --->Speakers
'
-----> Crossover --- Lows ---> Powered Subs.

Easiest is to use a 1/8 inch stereo to 1/4 inch splitter cable (1/4 mono's) and plug into the tape input. Then use the tape level knob.

IF you want to use sliders, then plug the spliter 1/4 inch plugs into two channels and set the PAN controls for these to opposite ends and then you have to adjust two sliders to control the gain.

Removing all the knobs from a section of the board where the bad fader is can be a hassle.and sometimes some of the nuts from jack or screws from some connectors.

You are probably better to order the part from Mackie to get the exact part. Most are made by ALPS and I get ones for some equipment from DigiKey.com or Mouser.com. However, it does take a bot o knowledge to get the correct part and sometimes requires cutting the shaft of one that is too long.
One MUST match the mounting holes, resistance value, length of throw AND the "taper". Yours will probably be a standard "Audio taper" for the main output.

is level pot defectives, needs to be replaced, u can change-them but is very comfusing, needs the same pot ref. u can find on electronics store, but probably dont find them easy, better send to repair. time spend to find them is long.

You may be getting a small amount of cross-talk. How high are the gain settings and sliders when this occurs? Also, can you describe the overall setup that you are using? I'll check the prints, but you should not be getting any volume unless the gains are maxed.

Dan

Yes, the ribbon cable is the 1st thing I would check. You can check the ribbon like this: Disconnect said cable from the channels. Connect cable connector from a known good channel to the problem channel. If channel sounds the same trace a signal through the channel op-amps.