First Steps In the service of a CD player

First steps in the service of a CD player - Carlos R. Villafane, CET

Basic Problems

Who we are dedicated to service, we know that the most important part (and most expensive) CD player, is the optical drive (optical pick-up, Figure 1). If the cause of the problem outside this module, the cost of replacing it could discourage the customer, it may cost about the same as a new device, so it is important to analyze all the alternatives we have, before providing the customer with a cost estimate.



The optical lens must function properly for the rest of the circuits do their job. No matter the brand of equipment, usually all perform these functions when the unit:

The optical reader moves to the center of the disk, until a switch "detector" is pressed. This tells the microcontroller that the reader comes to the starting position.

The laser light for a few seconds to detect if a disc in the tray. If the disk is present, return of the signal sent by the lens. If not returned, the microcontroller assumes there is no disk present.

If a CD, it automatically sends a pulse to the drive motor (spindle motor), which begins to rotate. At that time, the laser reads the information is at the beginning of the disk, in the central part (for reading a CD from the center to the periphery): Table of Contents (Table of Contents or TOC), the containing data on the number of songs recorded and the total time, this is shown on the display device. After this process, usually the hard stops, waiting for a user command.

Why should I explain this process? Because having an interruption in time to identify a disk, the device will not recognize it, hence the majority of technicians, usually the first thing they do is clean the optical lens.

Cleaning the lens

Enemy number one of the lenses is dust. A dirty optical lens can cause a number of failures, from "jumps" in the songs, to the impossibility of making the lectura.El dust, humidity, cigarette smoke and other, stick on the surface of the lens. It is advisable to manually clean it, preferably with products for cleaning camera lenses (or isopropyl alcohol) and cotton sticks (swabs), according to manufacturers' specifications. You can follow the recommendations given in Figure 2, but do not use chemicals like gasoline, acetone or thinner. Many of the current lenses are not made of glass, but plastic, so that the use of harsh chemicals or the stain permanently melts. Sometimes a dry cotton swab does very good work.



In fact, it should be noted that sometimes customers use a cleaning disc. As most of these discs only bring a small brush to "sweep" the surface of the lens, it is common not really clean the scum. So it is preferable to manual cleaning.

Signs

After performing the above process, you should check the signs. The first sign that we will see with the oscilloscope, is the RF (radiofrequency or Eye Pattern). Most computers have a test point on the card marked "Servo" with the letters RF. By connecting the oscilloscope, we have a signal as shown in Figure 3 while playing the disc.

If you have a team that seems to be reading, but no audio issues, we must investigate this signal. If this signal is present, it is an indication that the optical scanner and RF amplifier section is working properly, the problem is elsewhere sección.La signal should appear as clear as in the photograph, and should be distinguished clearly how diamond for the entire signal.

If you wiped the optical lens and did not get a good result, it is suggested that an adjustment to improve the quality of the reproduction of a potentiometer there disco.Generalmente letters RF, although it may be that in some models say or Best-PS Balance Eye Adjustment. Signal should be adjusted until it is as much of possible and minimize your vertical fluctuation, ie, that "jump" as little as possible.

Had to replace the lens, should take into consideration the type of servo system of the unit. Why? I will explain briefly. On computers that are ten years or more in the market, the servo system is almost similar, would have to do six manual settings for the device to work correctly (Figure 4).



But with the development of technology, such systems have been replaced by digital circuits (Figure 5). In fact, in some models fits only one control, and other signals are self-adjusted by sampling a signal (or feedback) that takes the microcontroller; other models fit completely on their own.



I hope these tips will be useful in the service bench. See you soon!

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Carlos R. Villafane, CBET, CET.