Symptom: a BMW car mounted multi-disc CD machine, model BMW-M91ZBM. The BAND key can not always be switched to DISC mode when performing panel operations.
    Troubleshooting: According to past experience, the failure of this type of CD is generally no power or 14-core control line problems. Then check the power, the measured voltage is 12.42V (engine is not activated), the results are normal. Then check the 14-pin control line section. The 14-wire control line connected to the CD player consists of two parts; the first part is from the CD to the luggage compartment, the second part is the tray itself, the two are connected by the plug. No abnormality was observed while measuring the first and second control lines.
    CD machine why there is no signal? At this time because the CD machine for a long time to use, the surface of the plug itself is bad or loose contact caused. To this end repeatedly plug, twist the middle plug, then the screen finally has DISC display. But then move the plug, the signal has disappeared. After replacing the control section of the disc, the screen is stable and the fault is removed.
    When the CD is re-tested, the screen shows the read disk error signal. Open the disc cover to look carefully, the disc cage to promote the load, self-test are normal. If the head can be moved to the outside by hand can also be automatically back, indicating that loading, tracking the servo system and mechanical part of the problem is not big (due to the back of the head to install, can not see whether the laser and focus action). Look at the CD, boot CD does not turn. Based on past experience to judge, the problem may be caused by the aging of the spindle motor.
    Since the CD does not turn, then certainly can not guide the disk. Unplug the third "SP" symbol on the control panel, with a regular battery (1.5V) directly to the spindle motor power supply, running normally. If the hand to the disc to add some resistance, the motor can still turn, indicating that the spindle motor no problem. And then use the multimeter 20V block measurement control board side, and then open the CD machine power switch, the screen without any display. And normally should have 5V voltage output. Turn off the power, with "2k" block test no response. Under normal circumstances, with the measurement SP side, multimeter should be similar to the capacitance when the display.
    Finally remove the CD under the cover, measured motherboard (CNP2479, D) IC671 (AN8377N) 11 #, 12 # feet and SP between the good conduction. It is determined that the IC671 drives the manifold to be damaged and replaced after troubleshooting.