20
APPENDIX A: Service Info
Bad Output
•
Are the
SUB ASSIGN
switches set
correctly?
•
Are the
MAIN MIX
Fader
and
SUB
Faders
turned up?
•
If it’s one of the
MAIN OUT
s
, try
unplugging all the others. For example, if
it’s a TRS
MAIN OUT
, unplug the associ-
ated XLR outputs. If the problem goes
away, it’s not the mixer.
•
If it’s a stereo pair, try switching them
around. For example, if a left output is
presumed dead, switch the left and right
cords, at the mixer end. If the left speaker
is still dead, it’s not the mixer.
Noise
•
Turn the channel Faders
,
EFX 1
RETURN
and
EFX 2 SEND
down,
one by one. If the sound disappears, it’s
either that channel or whatever is plugged
into it, so unplug whatever that is. If the
noise disappears, it’s from your whatever.
Power
•
Our favorite question: Is the
POWER
switch on?
Warranty Service
Details concerning Warranty Service are
spelled out page 23.
If you think your CFX Mixer has a problem,
please do everything you can to confirm it be-
fore calling for service. Doing so might save you
from the deprivation of your mixer and the as-
sociated suffering.
Of all Mackie products returned for service
(which is hardly any at all), roughly 50% are
coded “CND” — Could Not Duplicate, which
usually means the problem lay somewhere
other than the mixer. These may sound obvious
to you, but there’s some things you can check.
Read on.
Troubleshooting
Bad Channel
•
Is the
ASSIGN
switch set correctly?
•
Is the channel Fader
turned up?
•
On mono channels, try unplugging any
INSERT
devices.
•
Try the same source signal in another
channel, set up exactly like the suspect
channel.
GENERAL PRECAUTIONS AND CONSIDERATIONS
When setting up for a show, oftentimes you
are plugging into an AC power distribution sys-
tem you know nothing about. You may even be
faced with 2-wire outlets that are missing the
third safety ground pin. It’s a good idea to have
a three-wire AC outlet tester in your toolbox so
you can check the outlets yourself to make
sure they are wired correctly. These testers will
tell you if the polarity of the hot and neutral
wires is reversed and if the safety ground is dis-
connected. Don’t use an outlet if it is wired
improperly! This is to protect yourself as well
as your equipment.
If you find that you must plug into a two-
wire outlet, you will need to use a two-wire to
three-wire adapter (cheater plug). These come
with a metal tab that you put underneath the
center screw that holds the AC outlet faceplate
in place. This center screw
must
be grounded.
You can check it by connecting the adapter to
the outlet and then plugging in your handy-
dandy AC outlet tester.
NEVER bypass the AC
plug’s ground pin. This is
dangerous!
AC Power Distribution
The majority of AC outlets encountered in
homes and clubs (in the U.S.) are served by a
240VAC center-tapped service entrance trans-
former. This provides two phases of AC power
on either side of the center tap, at 120V each.
If lighting is used in a show, it is preferable
to power the lights from one leg of the service,
and power the audio equipment from the other
leg. This will help minimize noise from the
lights coupling into the audio (particularly if
SCRs, or light-dimmer switches, are used).
In order to minimize ground loops, the safety
grounds for all the outlets should be connected
to a common (“star”) grounding point, and the
distance between the outlets and the common
grounding point should be as short as possible.
