Marantz MM9360 Repairs, Troubleshooting, No Audio Output, Distorted Sound, Hum or Buzz Noise

7. REPAIRS

Only the most competent and qualified technicians should be allowed to service your unit. Marantz and its factory trained warranty station personnel have the knowledge and special equipment needed for repair and calibration of this precision instrument.

In the event of difficulty, call the toll-free telephone num- ber listed on the face of the warranty to obtain the name and address of the Marantz Authorized Service Center nearest you. Please include the model, serial number of your unit together with a copy of your purchase receipt and a full description of what you feel is abnormal in its behav- ior.

8. TROUBLESHOOTING

8.1 No Audio Output

1.) Power LED not lit:

Unit may be in stand-by mode if connected to com- patible Marantz product's stand-by output control. Line fuse is blown or power outlet is dead.

IF LINE FUSE HAS FAILED, REPLACE ONLY WITH SAME TYPE AND RATING FUSE.

2.) Power LED is lit but Protect LEDs stay on:

Amp module is in protect mode. Speakers have been internally disconnected from amplifier output and con- nected to ground until the protect fault is corrected. Out- put overcurrent, overvoltage and undervoltage faults will reset in about eight seconds once the fault condition is removed, while excessive DC offset or high frequency faults take about 30 seconds to reset.

Low Speaker Impedance: The amplifier may go into self-protect at high output levels if the actual speaker load impedance is much less than 4 ohms. To calculate speaker impedance for a given combination of direct- coupled speakers, use Ohm's law as applied to series and/ or parallel resistor networks, where each speaker (for this purpose) can be thought of as a single resistor, using DC resistance measurements.

Simply stated, speakers connected in series will add together their impedance. Conversely, two speakers connected in parallel will result in half the impedance, three parallel speakers a third the impedance, four speakers a fourth, and so on, assuming the speaker impedances are all the same. Don't use mismatched impedances in paral- lel. When using paralleled speakers, the available ampli-

fier power for that channel is evenly divided among speak- ers, so 100 watts driving two parallel speakers of equal impedance provides 50 watts to each speaker, etc.

3.) Thermal LED and Protect LEDs stay on:

An amplifier module is in thermal protect mode and needs to cool. The fan will continue to run while in thermal protect, and other modules will continue to func- tion.

4.) Power LED lit but no Signal LED activity

There is no input signal applied or input level controls are turned down.

8.2 Distorted Sound

1.) Clip LED is flashing regularly

Amplifier is being overdriven. Turn down the input level control, or reduce the output level from the signal source.

2.) Clip LED is not flashing at all

Amplifier input signal may be exceeding input headroom, which is greater than +12dBu, or 3.4V rms (measured us- ing continuous 1kHz sine wave). Incoming signal level higher than +12.8 dBu will cause distortion in the ampli- fier. Turning down the input level controls will not elimi- nate distortion if the input headroom is exceeded. Turn down the output level of the device driving the amplifier instead.

Additionally, an input signal may already be distorted be- fore it gets to the amplifier. Check to see if a piece of equipment in the signal chain before the amp is clipping. For best performance, the amplifier should be operated with input levels fully CW. Also check for damaged speaker drivers that could cause distorted sound.

8.3 Hum or Buzz Noise

Be sure that the power cord’s 3-prong plug is connected to a properly earth-grounded outlet. Lifting the grounding third prong may not improve hum or buzz and can create a po- tential shock hazard.

Hum is usually caused by ground currents flowing between different pieces of equipment. Ground currents can be minimized by using a single point AC ground for the sound system, and by using balanced connections with quality cable throughout the audio path.

Buzz, as well as certain audible high frequency tones, can be caused by environmental emissions such as lighting dimmers, neon lights, or computer equipment. Use bal-

8