NoteLaser diodes are the most sensitive components in CD players to electrostatic charge. Electrostatic charge is created by wearing synthetic clothing and friction. A small amount of static charge can be dissipated through the air in the room, If the relative humidity in the room air falls, however, the discharge is interrupted - especially during the heating period in winter, this should not be neglected. Damage to the laser due to electrostatic charge does not necessarily lead to immediate failure of the laser diode, a small charge can already cause a slowly dying laser diode - the reading quality slowly becomes weaker, a total failure occurs only after a few weeks. Working on the CDM drive is only recommended with appropriate equipment such as an anti-static working mat and additional discharge through an appropriate discharge wrist strap on the wrist. If a CDM drive is inconspicuous, the settings can be checked according to the following instructions and in two cases only the lower bearing of the CD spindle motor on the CDM-1 can be reworked. In case of uncertainty and a functioning laser drive, all other work steps should be disregarded.
CDM 1 Laser ServiceThere is a lot of information on the subject of laser voltage in the internet. Sometimes it is advised against changes, sometimes it is said, with an increase in the laser voltage you could breathe life back to a slack CD player.
However, an improperly working CDM-1 drive can never be restored by increasing the laser voltage. The causes of CDM-1 CD players are usually on the servo board, for example in broken ground feedthroughs or in a defective decoder board. A defective function due to insufficient laser voltage has never occurred before. Defects on the CDM-1 drive itself have mechanical causes, such as foreign objects that have penetrated, dirt on the laser and / or the mechanism or increased bearing resistance of the drive motor.
It is important to warn vigilantly against too high a laser voltage. It reduces the lifetime or even destroys the laser diode. The voltage is controlled at the emitter of a C548B transistor on the servo board.
The laser voltage is set with the marked potentiometer. As a guideline 500 mV apply when playing an original CD. For burned CDs, this value may be lower. The laser voltage can be reduced in a clockwise direction (with some CDM-0 reversed). The maximum value with tolerance specified in the service manual is 650 mV when playing the Philips test CD. But this is better left unchecked and assumes as a precaution that the laser diode from 0.65 volts is limited by overvoltage in their life and causes problems when playing burned CDs.
If you find a defective laser diode in your player, you must always replace the laser diode and the laser board together, as these form a coordinated unit. Every now and then replacement CDM-1 without the associated laser board are offered - such offers are completely meaningless. A laser unit that is connected to an existing one without the laser board shown leads with 50% certainty to the immediate destruction of the laser diode.