Testing sound system - ra820b1407700x(7700)

C. Preconditions for testing sound system, D. Testing sound system Model 140 (up to approx. 08/93)

C. Preconditions for testing the sound system

To determine the fault,	switch on radio.
Station signal strengths	set. NOTE: A music cassette or CD may also be played.
Balance control	set to middle position.
Fader	set to middle position.
Bass and treble	set to basic position by pressing both buttons at the same time.
Speakers	listen to each individually (e.g. with a tube).

Check bass reflex openings (1) on the bottom of the front and rear doors.

NOTE: Use, for example, a ball-point pen for checking. The insertion depth must be at least 50 mm.

Fig 1: Identifying Bass Reflex Openings - Front Door

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Fig 2: Identifying Bass Reflex Openings - Rear Door

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Depending on complaint

perform test as stated in D.

D. Testing sound system

Complaint:

Complete sound system does not operate

Fig 3: Complete Sound System Does Not Operate - Diagnostic Chart

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Complaint:

Door speaker on one side not operating

Fig 4: Door Speaker On One Side Not Operating - Diagnostic Chart (1 Of 2)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Fig 5: Door Speaker On One Side Not Operating - Diagnostic Chart (2 Of 2)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Complaint:

Bass speaker not operating

Fig 6: Bass Speaker Not Operating - Diagnostic Chart

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Complaint:

Bass speaker and rear door speakers not operating

Fig 7: Bass Speaker And Rear Door Speakers Not Operating - Diagnostic Chart

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Complaint:

Front speaker in base of mirror not operating

Fig 8: Front Speaker In Base Of Mirror Not Operating - Diagnostic Chart

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Complaint:

FRONT OR REAR SPEAKERS NOT OPERATING

Test step	Test scope	Tester/Test connection	Test requirement	Specification	Possible cause/Remedy
1	Fader (R26)		Turn fader (R26) to end stop	Line on fader control (blue connector plate)	(R26)

Complaint:

STEREO SOUND DISPLACED TO THE SIDE AT REAR SEATS, IN ORDER AT FRONT SEATS

Test step	Test scope	Tester/Test connection	Test requirement	Specification	Possible cause/Remedy
1	Check speaker cover of rear left and right door trims for damage or wrong versions	Handlamp (pencil-type lamp)		Speaker membrane must be recognizable through the cover	Speaker cover of door trim

Complaint:

STEREO SOUND DISPLACED TO THE SIDE AT FRONT SEATS, IN ORDER AT REAR SEATS

Test step	Test scope	Tester/Test connection	Test requirement	Specification	Possible cause/Remedy
1	Check speaker cover of left front and right door trims for damage or wrong versions	Handlamp (pencil-type lamp)		Speaker membrane must be recognizable through the cover	Speaker cover of door trim

Special tools

Fig 9: Identifying (126 589 20 63 00)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Fig 10: Identifying (124 589 00 21 00)

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

COMMERCIALLY AVAILABLE TOOLS AND TESTERS

Designation	e.g. Make, Order No.
Multimeter	Fluke, 23 DB Thorn EMI Avometer, 2003