Manual MB Quart dsc1000 1 (page 14 of 16) (English, German)

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A M P L I F I E R S

ENG

TROUBLE SHOOTING

The key to finding the problem in a misbehaving 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 all MB Quart amplifiers:

The diagnostic system will shut down the amplifier, until reset by turning the

head unit off, and back on. This state of affairs will be indicated by the front

panel PROTECT LED lighting up under the following conditions:

1 - A short circuit on the loudspeaker leads.

2 - An internal amplifier fault that causes a DC offset on the loudspeaker

output.

Should the amplifier go into diagnostic mode, simply disconnect all RCA and

speaker leads, while keeping +12 volt, power ground and remote leads connected.

1 - Now turn the amplifier back on, and if the diagnostic LED lights, the

amplifier has an internal fault.

2 - If not, plug the RCA cables back, and reset the amplifier. If it goes into

diagnostic now, the fault lies in the input, either with bad cables or source

unit.

3 - If the amplifier seems fine with RCA cables plugged in, connect the speakers,

one at a time, and if one of the speakers or its wiring is faulty, it will

activate the diagnostic system.

Amplifier heatsink overheating

The amplifiers will shut down when the heatsink temperature reaches 80° C,

and turn back on once the unit has cooled down below that point.

Causes of overheating:

1 - Inadequate cooling - relocate or remount to provide better natural airflow

over the fins.

2 - Driving high power levels into low impedances - back off on the volume

control, and/or make sure you are not loading the amplifier with less than

the recommended loudspeaker impedance.

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 +12 volt

and ground terminals, is 11 volts or more.

3 - Check all +12 volt and ground connections.

Fuses blowing

1 - The use of loudspeaker impedances below the recommended minimums

will draw more current - check.

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 an amplifier fuse blows continually, with only +12 volt, ground and

remote leads connected, the amplifier 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 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 occurs when amplifier level controls are

turned up too high - readjust according to the procedures in section ”Setting

up systems after installation for best performance”

2 - Another major problem that can cause excessive hiss, is a noisy head unit

- unplug the amplifier input RCA cables, 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. Remember to isolate the

problem - first unplug amplifier input RCA cables, if the noise is still present,

check the speaker leads, if not, plug the RCA’s back, and investigate the source

driving the amplifier, one component at a time.

A ticking or whine that changes with engine RPM

1 - This problem could be caused by radiation pickup of RCA cables too near

to a fuel pump or a distributor, for instance, - relocate cables.

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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MB Quart dsc1000 1 Manual

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