MB QUART MX-4 - Manual (Page 20)

TROUBLESHOOTING A SYSTEM
The key to finding the problem in a troubled sound system is to isolate parts of that system in a logical fashion to track down the
fault.
Description of the Diagnostic system built into the MX-1 & MX-3:
1. Clipping Indicator: Red Illumination when signal is clipped.
2. Normal Operation: Green Illumination, when signal is unclipped up to 9volts.
The diagnostic system will not shut down the MX accessories or the amplifier(s), although the amplifier(s) own protection circuitry
may shut the amplifier(s) down should a fault status occur. At which time you will need to consult the owners manual for that
particular amplifier.
Low output power
1 - Check that level controls have been set up properly.
2 - Make sure that the battery voltage, as measured at the amplifier’s and MX accessories +12 volt and ground terminals, is 11
volts or more.
3 - Check all +12 volt and ground connections.
Fuses blowing
1 - Insure that the voltage to the unit does not exceed 15 volts.
2 - A short on the main +12 volt cable from the battery to the vehicle chassis will cause the main fuse to blow.
3 - If the MX accessory is blowing fuses continually with only +12 volt, ground and remote leads connected, the unit may be faulty.
System does not turn on
1 - Check all fuses.
2 - Check all connections.
3 - Measure the +12 volt and remote turn on voltages at the amplifier and MX terminals. If these are non existent or low, take
voltage measurements at fuse holders, distribution blocks, the head unit’s +12 volt and remote leads to localize the problem.
Noise problems
System noise can be divided into two categories, hiss, and electrical interference.
Hiss, or white noise
1 - High levels of white noise usually occur when level controls are turned up too high - readjust according to the procedures in the
appropriate application section.
2 - Another major problem that can cause excessive hiss, is a noisy head unit - unplug the MX input wires, and if the hiss level
reduces, the source unit is at fault.
Electrical interference
The inside of an automobile is a very hostile electrical environment. The multitude of electrical systems, such as the ignition
system, alternator, fuel pumps, air conditioners, to mention just a few, create radiated electrical fields, as well as noise on the +12
volt supply and ground. To try and eliminate this noise, run a wire from the radio ground wire to the ground input on the MX unit.
A ticking or whine that changes with engine RPM:
1 - This problem could be caused by radiation pickup of RCA cables that are too close to a fuel pump or a distributor.
2 - Check that the head unit ground is connected straight to the vehicle chassis, and does not use factory wiring for ground.
3 - Try to supply the head unit with a clean +12 volt supply directly from the battery +, instead of using a supply from the in dash
wiring/fusebox.
A constant whine:
This type of noise can be more difficult to pinpoint, but is usually caused by some kind of instability, causing oscillations in the
system.
1 - Check all connections, especially for good grounds.
2 - Make sure that no speaker leads are shorting to exposed metal on the vehicle chassis.
3 - RCA cables are notorious for their problematic nature, so check that these are good, in particular the shield connections.
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