Sony CDP CX400 – CX450 –Disc drive – Troubleshooting

Sony CDP-CX235  CDP-CX270  CDP-CX335  CDP-CX400  CDP-CX450 CD Changer - Disc does not spin – Disc spins, but does not read the TOC [Table of Contents]

The CD Changer can be divided into two main areas: The Changer mechanism that selects the disc from the tray table and the CD disc Playback mechanism that reads the track of information from the disc and produces audio.  The Changer mechanism periodically requires mechanical adjustment to compensate for wear of parts over a time. This will make sure the correct disc is identified and selected.  The Playback mechanism is more involved, requiring an understanding of the playback details for efficient repair.
Failures in the playback mechanism can be classified into these symptoms:
• Disc doesn’t spin.
• Disc spins but doesn’t read the disc’s table of contents (TOC).

Disc Doesn’t Spin
Before the disc spins, the sled must be at home position, the laser must be turned on, and focus must be found. All of these things can be checked easily.
Sled
In the CD Mechanism, you will manually move the optical assembly away from home position. When you power up the CD changer, the sled motor will turn, moving the optical assembly to the limit switch. This proves the sled assembly is basically OK. As you move the gears make sure they move without binding. The limit switch must be tested with an ohmmeter.
The sled check procedure is as follows:
1. Shut off power by pressing the POWER button if necessary.
2. Locate the large white gear in the CD Mechanism and rotate it so the optical assembly moves away from the spindle motor shaft (which is the home position).

3. Press the POWER button and the optical assembly should return home. (The tray table should also rotate at this time.)  When the optical assembly reaches home it should close the limit switch and power to the sled motor will stop. 

The white gear should be free (unpowered), proving the limit switch is OK. You can also test the limit switch with an ohmmeter.

Laser
It is best to measure the laser brightness with the Leader model 8001 laser power meter. During focus search, the laser power is 0.03mW in this model CDP-CX235 200 disc CD changer. The procedure is:
1. Remove the magnet assembly by pulling it outward at a 2 o’clock direction.

2. Without CDs in the tray table, momentarily place your fingers between the disc tray and the luminous sensor as you turn the power on. The changer will mistakenly sense many discs, attempt to load them and turn on the laser.

3. Through the opening in the black magnet holder you can measure the laser light with the laser meter probe. See the picture in step 1. DO NOT LOOK AT THE LASER LIGHT. You may see the laser reflection by placing a piece of white paper in the laser path.
4. Reinstall the magnet assembly.

DISC WON’T SPIN FLOW CHART

Focus

Electronic Focus is a two-part operation. The first part is when Servo Control uses the driver to move the lens away from the disc and then slowly back toward the disc looking for the focus point on the disc’s information layer. This first part is called “focus search”. 

The second focus operation occurs when focus has been identified by servo control. This is called “focus servo”. The transition from search to servo is marked by a HIGH at the FOK test point when focus is found.  The search operation can be observed. The servo operation can be checked at the FOK test point on the BD board with a scope can check the servo operation. The procedure is as follows:

Focus Search Mode

1. Enter the Adjustment Test Mode by unplugging the AC power from the changer.

2. On the main board, connect the “ADJ” test point to ground. In the CDP-CX235, ADJ is under the large 1-farad capacitor. Ground is the negative lead of the large 1-farad capacitor.

3. Plug the CD changer into AC. The unit is in the Adjustment test mode. This mode can be used to manually alter some servo parameters.

4. Press the front panel CHECK button while in this test mode. The laser will come ON, the spindle motor will turn, and the optical lens will move in the focus search operation.

Focus Servo Mode
5. To make the transition to focus servo, a disc must be inserted so the laser can focus on its information layer. 

You must exit the test mode to install a disc. Temporarily remove the jumper wire’s ground end and unplug power.
6. On the BD board locate the RFO and FOK test points and attach your scope probes to them.
7. Plug the changer into AC, press the POWER button and then the OPEN/CLOSE DOOR button. Insert a disc (label to the right).
8. Press the OPEN/CLOSE DOOR button again to chuck the disc. The door will close and the disc will be loaded into the CD mechanism (chucked).
9. Re-enter the adjustment test mode by unplugging AC and reconnecting the ADJ test point to ground.

10. Watch your scope as you apply AC power. If the FOK line goes HIGH, focus has been found. The transition from search to servo is then performed within Servo Control. At this point you know the laser is working and the focus driver part of the IC is good enough to achieve FOK. The following waveform compares the RF output to the FOK signal. This waveform shows RF signal goes HIGH as soon as focus is found. (The spindle motor also starts when FOK goes HIGH producing the RF waveform that follows.)

If FOK does not go HIGH, increase the scope’s time base and look at the RFO signal for a rise in voltage as the lens repeats the focus search operation in this test mode. NO RFO means there is no signal from the optical assembly. This could be because there is no laser light or no power (ribbon cable). If there is an RF output during focus search, yet there is no FOK signal, the source of the FOK signal can be checked.

FOK comes from the RFO signal that is derived from the optical detectors A-D. When the RFO reaches a set threshold, FOK goes HIGH proving that there is light returned from the information of the disc (laser and focus OK)

RFO can be compared to FE to see if there is an output before condemning the optical assembly. If there is an output from both, the optical assembly and RF amp IC are OK and the likely suspect is a defective Servo Control IC that makes the FOK signal.  

An easy way to see if there is RF under this defective condition is to repeat the Search operation. In the ADJ Test Mode, press the front panel CHECK button. This CHECK button just repeats the search operation, but the servo operation that normally follows will be inhibited so the disc will not play. Place a scope probe at the RFO and FE test points.

11. Remove the jumper wire between the ADJ test point and ground.

Disc Spins But Doesn’t Read The Disc’s Table Of Contents (TOC)
If the disc spins, Servo Control knows the optical assembly is at home position and focus was found (so the laser must be good too). Now the quality of the RF signal that is output, and the tracking and spindle servos are in question.  S

Since the optical assembly and the servo circuitry are linked, it is difficult to determine if one or the other is bad without replacement. The severity of the testing waveform usually distinguishes. If the waveform is extremely bad, the circuitry is often at fault caused by an abrupt failure. A waveform out of spec is often caused by an aging optical assembly.  The RF and tracking servos can be tested, but the spindle motor servo cannot be tested separately.

RF Output
The normal RFO measures about 1.2Vp-p. As the optical assembly ages it drops until a critical level of about 0.9Vp-p, causing skipping, or to about 0.75p-p, causing no playback.  The previous S curve waveform shows that the RF signal appears once focus is achieved. When the disc is beginning to play, the RFO level should rise quickly and produce a waveform. The RF waveform will continue if the tracking and spindle motor servos operate. Comparing the RFO and tracking error signal permits you to see if the optical assembly is weak and check the tracking stage at the same time.

Tracking Servo
The tracking servo consists of an electronic closed loop circuit. The loop is completed by Servo Control as soon as focus has been identified using the FE signal.

DISC SPINS, BUT DOES NOT READ TOC FLOWCHART

When the tracking loop is broken, the TE waveform changes from what looks like .5Vp-p of noise to a large broken waveform of 1.5Vp-p (Ch 2).
The RFO signal shows losses of RF where the laser is crossing tracks.

An open tracking loop is not common and is usually caused by foreign objects in the optical assembly, its ribbon cable or a bad driver IC.

Spindle Servo
Even though the spindle motor turns the disc, its servo loop may not be closed. A defective spindle motor servo produces RFO data that alternates between good and bad (even tough they both look the same on the scope). Looking at the LOCK test point at the Servo Control tells you if the spindle motor loop is closed, since the focus and tracking servos must work before the spindle servo can close. For example, if the tracking servo were defective, the spindle servo loop cannot close because the RFO data is unreliable. Therefore the other servos must be checked prior to this check. It also takes a while to process the RFO data to establish a spindle motor lock so the spindle servo is the last servo to engage. This is shown when comparing RFO (Ch 1) to the LOCK test point (Ch 3).

If all the other servos check OK and the LOCK test point remains LOW (spindle servo defective), the common cause is the motor itself.