I own a Mackie CFX20. It isn't the MKII. The effects are very weak, and they buzz a little when you try to use them. How can I fix them, and is a service manual available?

Please post some more detail of how each channel is set up and what you have assigned where. My guess is that reading the manual may sort your issues.

You say the clip light is always on, as the only clip lights on this mixer are on the effects channel and the master output and you do not say which is on there are a number of possibilities. You may have the effects turned up too far as this should not be showing, just maybe blinking, turn them down on efx2 on all strips as well as on the effects processor and see if this helps. If it does you may be able to find where the hum is coming from by gradually increasing each until you find it.

If you are getting the clip on the main mix master and you are not being deafened and the humming sound is coming from the speakers not the mixer you may have a subsonic signal getting into the mixer. Disconnect all inputs and if this cures it go through until you find where it is getting in and sort that.

If the humming is coming from the mixer it is possible that the smoothing caps on the PSU are dying, you do not say if you are getting normal sound as well as the humming from the mixer.

When asking for help please try to give as much information as possible

What makes you say it works fine if you are getting no output? Have you just got it turned down?

If headphones have both sides working, it is NOT the main fader. It would most likey be the driver chip for the failed side that has been blown. This is common problem when people fail to power the mixer from the same receptacle or power conditioner that amps and other connected equipment are powered from. Ground bounce damages the circuits. The balanced outputs are driven by NJM4560 op amps which are likely surface mounted 8pin chips... .

Here is service manual:

http://elektrotanya.com/mackie_cfx20_sm.pdf/download.html

Scroll down to "get manual" and click on it to download. Ignore other download links for viewers.

The channel solo does NOT kill the subs for the channel, so if you have the subs going to effects and back to the mains that path will still get to the mains appearing as bleed Here is the service manual for the CFX20 which is just more channels of yours.

http://elektrotanya.com/mackie_cfx20_sm.pdf/download.html

Scroll down to "get manual" and click to download. Ignore other download links which are for viewers, etc..

Shafts will SURELY break if you try to straighten them. Replacing these requires labor of removing a lot of knobs and screws... cost of the pots is minimal.

sounds like a blown output transistor

Yopu do NOT clean the pots... if you have noisy sliders, get some CRC226 at Home Depot in the electrical dept. Spray a small bit in the center of the slot for the slider and run the slider up and down. Use sparingly and apply a tiny amount once more. The sliders are NON_REPAIRABLE if this won't fix them and major disassembly is required involving removing the round knobs, fader knobs, screws and other nuts on the jacks. Hours of work. Pots require desoldering tool and use of soloder wick and plunger type removal tools often causes damage to the circuit board.

Here is the complete service manual:

http://elektrotanya.com/mackie_cfx20_sm.pdf/download.html

Make sure the PAN knobs are centered...

Also you can do a lot of troubleshooting with headphones in monitor jacks, etc.

Remember to use BALANCED lines out of the mixer which are either XLR or TRS type cables.