Laser 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 Service

There is a lot of information on the subject of laser voltage in the network. 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.

Laser voltage Philips CD104

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.

adjust Laser voltage

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.

Set focus

The focus is adjusted at the bearing screw of the drive motor with a Torx screwdriver while the CD player is running.

Fokus setting Philips CD104 CDM1

The voltage is measured for the focus control on the right pin. Since a CD is never completely flat (which is compensated by the focus control on the servo board), the reading changes with each revolution of the CD. In the last song (on the CD outside) these fluctuations are higher. Since the data layer of a self-burned CD is slightly different (which is why an "audible" skipping at the end of the CD is more common in home-burned CDs), the best thing to do is to start a home-burned CD. Adjust the bearing plate to the lowest possible measured voltage value.

In some cases, losing focus can have other causes, For example, if the tracking does not work without resistance or the axial angle of the entire laser stock is no longer correct.

set fokus Servo

Tracking radial motor

The tracking control, which guides the laser from beginning to end of the CD, is controlled by a magnetic field on the Philips CDM1 drive, which moves an aluminum arm with the laser stick into position. The most common mechanical cause of suspension of the playback is, after the loss of focus and increased bearing resistance in the axial CD motor, too high a bearing resistance in the radial motor of the tracking control. The axis of this radial drive is a stainless steel shaft on the CDM1, which is ball-bearing at the top and bottom. After different material expansion, the voltage on these ball bearings and thus their resistance increases until the electrical tracking control this can no longer compensate. The excessive bearing resistance manifests itself in simple cases in dropouts or a failure of the function at title jumps. To a greater extent, electronic track control can be damaged by overloading.

The bearing tension is adjusted to the nut of the stainless steel shaft, which can be seen in the middle of the bottom of the CDM1 unit on the following photo.

Philipc CD304

The axis of the tracking control can not be pulled out completely. The axle accommodates distance caps, discs, rubber rings and a spring washer, from which something quickly reaches the surrounding magnets. In this case, the radial drive must be completely demoted from the base plate to put everything back in the correct order.

Philips CDM0

It is sufficient if the axle is inserted flush after loosening the nut. At the top, this gives the hexagon head of the axle sufficient clearance to access the upper ball bearing.

Philips CD104 Revision

Some silicone oil can be applied with a syringe on the bearing capsule. Through the small gap between the inner bushing and capsule plate, this oil gets into the interior. To distribute it evenly, turn the axle by hand.

Philips CD 104

Repeat the process on the second bearing and then move the axle back to its original position.

Philips CD304 Revision

Put on the washer and only tighten the nut with your fingers. While the mother is gently turned on, with the other hand, the laser stick must be used to control the bearing clearance. Just move the laser stick up and down gently. The bearing clearance is visible between the nut and the outer bush of the bearing. The nut is only tightened until the bearing clearance is minimal and the rotary arm remains free to move without excessive bearing tension.

CD 204 Modifikation

To test a sufficiently low bearing resistance, lay the CDM1 flat and place the ribbon cables over the pivot arm so that it can move freely. Measured with a Nederwaage, a force of 30mN from start to full swing of the rotary arm must not be exceeded. Lightly touched with the finger, the rotary arm should swing very smoothly from one end stop to the other and always come to a standstill in the same approximately center position.

CDX Revision

Finally, the focus must be reset.

Scanning angle of the laser stock

The laser beam should fall almost at 90 ° to the CD so that the reflected data sample falls within the intended range of the monitor diode. In the Philips CDM1 drive, the entire laser stick is mounted on a rotating arm to guide the laser beam in the track from the beginning of the CD to the end. The axis of this rotary arm can be seen in the middle of the following photo on the underside of a CDM1 unit. The axle is mounted centrally on a bracket with a nut, the bearing block itself is fastened with two Torx screws. After loosening the two screws, the axis can be moved to adjust the angle to the CD.

Due to the precise and solid construction of metal, there is no change in this angle and a setting is usually not necessary. Also, the bundling of the reflected data sample is so excellent that a wide tolerance range for the angle adjustment is possible. For the angle adjustment, therefore, the ease of movement of the axle has a higher priority. If this angle is adjusted, the tension in the upper and lower ball bearings of the axle also changes. The reason for a lack of function is often a too high resistance of the bearings, which then complicates the tracking control.

Philips CDM1 radial tracking

The angle only has to be adjusted if the two screws of the bearing block have been accidentally released, or if the entire magnetic radial drive is exchanged with laser stock. Since this unit always has to be replaced with an associated laser board, such an exchange is actually eliminated. It remains next to laser board, radial tracking control and laser stick on the aluminum body of the CDM1 unit, only the axial motor for the rotation of the CD, which is easier to swap, but usually only requires a bearing maintenance and adjustment. In case of an actual defect on the laser stick, it is better to change the CDM1 unit.

For the remaining case of an inadvertently released bearing block, a glass test CD and a special mirror are needed to adjust the Philips angle. Unfortunately, both are no longer available and it must be another solution. For the test CD is a transparent CD, which is sometimes at 50 or 100 spindles for CD blanks on top. On this transparent CD, a thin line is applied with a ruler and felt-tip pen that runs approximately through the center of the possible data area.

angle setting

The second measuring instrument, the mirror, we can make superfluous. The mirror with cutout should be placed on the upper lens of the laser. If now the test CD was launched, a faulty angle adjustment could be determined in a certain direction. The CD and the laser stick was turned until the lens is centered under the line through the CD. The viewing direction was dictated by the mirror, where the reflection of the line from the CD is not visible and is hidden by the line on the CD.

The viewing direction can also be ensured in other ways. If the lens is centered under the line and the line is also centered through the tracking control axis

test cd

It is only seen with one eye and the light should fall straight on top of the lens.

checking laser angle

With the light coming in as straight as possible from above, the line on the CD casts a shadow over the lens. On the bare aluminum rim that surrounds the lens, this shadow is clearly visible. If this shadow deviates by more than 4mm from the congruent lines on aluminum body and CD, the angle must be readjusted. With less than 4mm a setting is not necessary and should not be done so far that the shadow is exactly covered by the line on the CD.

The following photo shows the shadow, but is not photographed from the point of view for clarity.

Philips CDM1 Laser

The angle must be measured again over a second staggered position. If a setting is necessary, the two screws of the bearing block are only released so far that it can be moved with some force until the correct position has been measured. In order to correct a misaligned angle over both measured axes, patience and instinct are needed. Afterwards, both the focus and the bearing resistance of the track control must be readjusted.

second measuring

CD spindle motor, Hall motor

As the bearing resistance increases due to wear, the CD motor stops running. The word wear here refers to a normal process that can not be avoided even with high-quality components such as a stainless steel shaft in a brass bushing. The CDM-1 drive usually requires only one maintenance after 25 years.

Disassembled drive motor of the CDM-1 laser unit.

CDM1 Philips CD304

To remove the motor, first loosen the two screws of the motor bracket with a Torx screwdriver.

bracket Philips CD104

After removing the motor bracket, the lower bearing plate is offPlastic to see inside the magnet.

Lagerschraube im Motorbügel

After releasing the nut, the bell can be pulled straight up.

Abgenommene Motorglocke CDM 1

The motor board is not attached separately and can also be taken.


After the snap ring has been removed from the motor shaft, this can be down be pulled out.

CD Spindel

For most units, a thorough cleaning of the Bushing with benzine, the stainless steel shaft can with a 1000er sandpaper be settled. The play of the wave in the socket may not afterwards to be too big. The shaft may without mineral oils or adhesive in the socket inserted.

Laufspuren an der Antriebswelle

The remaining contact point of the shaft is the lower bearing plate Plastic, which also serves to adjust the height of the spindle in the form of a screw. At an average of 350 to a maximum of 500 revolutions per minute, a radial ball bearing is not necessary, here is enough a lubricious plastic. On the picture below there is a storage plate on the right normal use after 20 years. On the storage plate are about 100 millions of revolutions of the spindle axis occurred - the CDM-1 unit worked error-free without any impairment. On the left side of the picture a storage plate behind 10 years of continuous operation and about 1.8 billion revolutions. The storage plate is around run down to 0.8 mm. The CD was thus no longer in focus and the Servo board did not switch the drive motor.

Abnutzung an der Lagerschraube

An adjustment of the bearing plate to the run-in dimension brings the spindle again in the area necessary for the focusing. Because the run in place rarely exactly centered and the bearing surface of the spindle through the trough shape is larger, is only adjusting the bearing plate, the bearing friction further increased. The spindle height can be ground flat. For surface grinding turn the Bearing plate inverted in the hanger, so that the bearing side easily raised from the hanger stands. Put 1000s of sandpaper on a mirror to obtain a flat grinding surface.

Planschleifen des Lagertellers

You can grind the bearing plate flat by the hanger give the right position. For grinding, I always use the same strap, so that the remaining in the CD player does not show the ugly sanding marks.

Motorbügel mit geplanter Lagerschraube

Then screw the bearing plate back into the bracket in the correct direction and mount the entire unit in reverse order. On the Storage plate should like the stainless steel shaft no mineral oils or Adhesive lubricants are applied. For presetting the spindle height is the bearing plate screwed in so far that an air gap of just under a millimeter arises between the ring magnet on the engine bracket and the bell of the engine, so that the bell can rotate freely with spindle. The final fine adjustment of the bearing plate is made during operation: set the focus.

Inner laser lenses

In rare cases, dirt may fall past the upper lens and a cleaning of the underlying lens is required. After pulling out the ribbon cable can twist the entire laser body by lightly against to be pulled out clockwise.

Platine der CDM Laserdiode

Do not loosen the screw because no dirt can get inside.

Entnommener CDM Laserstock

Align monitor diode

Without measuring station, only the following rough alignment is possible. A function is not guaranteed. This part should not be performed and is for illustrative purposes only.

Körper der Monitordiode mit entnommener Platine der Laserdiode

The two upper lugs on the aluminum body of the laser diode must be the buck of the enclose aluminum body of the monitor diode.

Sicht in den Körper der CDM Monitordiode

The fine line visible through the lens now has to be aligned with the monitor diode by turning it.

Ausrichten der CDM Monitordiode

The air gap for height adjustment should be measured with a feeler gauge before disassembly. But that too is usually too inaccurate. An exact alignment is only possible with a measuring gap.

Höheneinstellung der CDM Monitordiode

Set CD feeder

Famous like the CDM-1 drive itself, the CD tray does not quite fit in and needs the "Philips pusher" - Press the drawer on the last centimeter by hand.

Philips CD304 CD Lade schließt nicht ganz

The cause is often suspected of the rubber belt on the motor drive. With a new rubber belt, the cause can often not be resolved.

Gummiring des CDM1

The mechanics of the CD's prescriber are the cause. The bow of the caster is minimally bent. When retracting the CD tray, the mechanism therefore tries to exert a higher pressure on the CD - the resistance on the last cm path of the tray is thus too high.

Zu hoher Anpressdruck auf die CD

The bracket of the roller can be directed at the top with a screwdriver. With the right setting, the drawer runs cleanly without resistance to the end stop and the bracket brings just enough contact pressure to the CD that it can be accelerated without excessive slipping when starting the function.

Richten der Lagersteuerung

To prevent re-bending, a felt glider can be attached as a spacer. But it should not load large weights in the middle of the case lid of the CD player.

Stahlblechkorb des CD Einzug

If the battery is running in at the rear, but it is very slow overall, the transistors on the control board of the charger should be replaced. A defect in the drive motor for the load, was so far only once to find, so it is quite unlikely if the CDM feeder installed clean and the cables of the engine, while not squeezed.

Steuerung CD-Einzug

Installation and adjustment

All moving parts can be lubricated with a mounting paste. The area of ??the rubber ring and the running plate for pressing the CD must remain free from this.

Mechanik schmieren

fter installation, the adjustment of the mechanism is made. After inserting a CD, the left screw can be loosened to change the position of the CD feeder with the white plastic so that it does not come into contact with the rotating CD during operation. The right-hand screw is screwed in so far that, with the CD inserted, a small air gap of 3 sheets of paper remains between the end of the screw and the steel basket. The guide rollers of the extending CD tray can compensate for such irregularities by means of the spring, but not remove so far that the CD feeder jumps out of its leadership.

Einzug justieren

Finally, a uniform air gap to the front of the unit is set on the two screws of the intake panel.