This invention relates to testing and troubleshooting of digital disc players and data storage drives. More particularly, it relates to a novel apparatus and method for detecting and recording random and/or intermittent errors made during play by digital disc players or the like, such as those that read or play audio compact discs, CD-ROM discs, or digital versatile discs (DVD). The invention can also be used to detect and record intermittent errors in analog or digital signal paths, as discussed below.
For simplicity of explanation in this disclosure, and merely by way of example, some discussion here addresses testing of players that use various conventional rotating disc media encoded with the CD (Compact Disc or Red Book) format, such as CD-DA (Compact Disc Digital Audio), or DVD (Digital Versatile Disc) formats, where pulse code modulated (PCM) audio, video, or other data is encoded, with error correction and other features, using long strings of physical pits written helically on the reflective surface of a polycarbonate disc. However, the invention shall apply equally well to other present and future formats, such as DVD (digital versatile disc) formats that may use Direct Stream Digital (DSD) encoded data; or future formats where rotating discs or other digital media are played. This would include future solid state media such as photorefractive volume holographic storage (PVHS), where the storage medium is not physically rotated, and where data is accessed by directing a laser beam to various physical portions of a crystal or other solid.
Digital disc systems are known for unprecedented fault tolerance, accuracy and reproducibility. Properly functioning digital disc player systems are generally impervious to noise and major output signal defects due to robust error correction and modulation schemes. When problems with digital disc players do occur, however, their appearance is often intermittent and difficult to discern. Although there tends to be general agreement Concerning format specifications for digital discs, manufacturers of digital disc players have freedom to employ differing designs in their players. This results in a wide variety of player designs, with differing individual error and failure modes, which compounds problem diagnosis.
Aside from problems arising from physical impact and damaged or soiled disc player media, there are component or system problems that manifest themselves in subtle ways. Some of these problems cause random or intermittent errors which are extremely troublesome for CD player repair technicians to locate and diagnose. Time spent on signal or output monitoring in order to make a diagnosis in these cases often can far exceed time spent on repair or replacement of the failing individual components.
Troubleshooting digital disc players is also difficult and, time-consuming because of their complexity. Error correction, synchronization and modulation require electronic and logic circuits; tracking and focusing require optical and electro-mechanical servo systems.
Many intermittent-type failure modes result, in part from: [1] temperature-induced stresses; [2] specific conditions such as wear and accumulation of debris and dirt on mechanical components; [3] factory assembly errors that result in momentary malfunctions; [4] environmental factors such as humidity and dust; and [5] systemic factors resulting from the use of specific assemblies or structures, such as the use of arm-mounted pickups that move in an arc or tangentially across the surface of the storage medium, cable stresses and fatigue, bearing failures, and other electrical, electromechanical, or mechanical defects.
These all present challenges for diagnosis, repair, testing and service of digital disc players. Often, when a digital disc player fails intermittently, it must be tested at length prior to and after repair, in an effort to establish which components or systems are at fault, as well as to provide confirmation that repairs are properly effected and will solve the problem where it originates.
Error correction, synchronization, and modulation all play roles in determining actual signal output. With errors in the pickup signal corrected, compensated or masked by the playback systems in use, the character of digital disc player problems or malfunctions becomes even more intermittent and subtle.