Technics-SJMD100-md-sup1 维修电路原理图.pdf

WARNINGThis service information is designed for experienced repair technicians only and is not designed for use by the general public. It does notcontain warnings or cautions to advise non-technical individuals of potential dangers in attempting to service a product.Products powered by electricity should be serviced or repaired only by experienced professional technicians. Any attempt to service orrepair the product or products dealt with in this service information by anyone else could result in serious injury or death. 1999 Matsushita Electric Industrial Co., Ltd.All rights reserved. Unauthorized copyingand distribution is a violation of law.ORDER NO. AD9903069S2Colour(K) . Black TypeAreas(E) . Europe.(EB) . Great Britain.(EG). Germany.SJ-MD100Minidisc Deck$ This document is supplementary to thefollowing Service Manual:Supplement for technical information about MD.$ ContentsArea Code(E) (EB) (EG)Order No.MB9902001C2Model No.SJ-MD1001. Measuring instruments and special tools$ PurposeO ROMPart No.: RFKV0006O ROMPart No.: RFKV0014O Extension Cable KitPart No.: RFKZJMD100EKO Laser Power MeterModel No.: LE8010Made by Laser ElectricTest DiscExtension Cable KitLaser Power Meter2. Basic Knowledge of MD3. Operating Procedures4. Troubleshooting Guide for MD Servo CircuitRadioFans.CN 收音机爱 好者资料库SJ-MD100 2 Construction ofmagnet optic discU Construction of an MDY The playback-only MD and the recordable MD are exactly identical in size and shape.Y The figure below is a cross-sectional diagram of an MD disc. The diameter of an MD disc is 6.4 cm, approximatelyhalf that of a CD, and the thickness is 1.2 mm, the same as a CD. Similar to a CD, only one side of an MD disc isused to store data.U Materials used in an MDY The MD disc is made of polycarbonate, the same material that is used for a CD. Polycarbonate is a type ofengineering plastic that is highly resistant to temperature and humidity, as well as having excellent wear andimpact resistant.Y A clamping plate is mounted in the center of the MD disc, and when the MD is loaded into a player, a magnet in theplayer attracts that metal plate to secure the disc in place. If the MD disc were to be secured by clamping it fromabove and below similar to a CD, it would be necessary to have a hole pass through the center of the MD cartridge,which would reduce the amount of space available for attaching a label. By using this magnetic method of securingthe disc, the entire front side of the MD cartridge can be used as a label area.Y Because of the metal plate mounted at the center of the MD disc, the center of the cartridge is 2 mm thick, slightlythicker than the rest of the cartridge.Y To protect the MD disc from dust, fingerprints, and other things that might hinder the reading of the recordedsignals, the disc is stored inside a cartridge similar to that of a floppy disc. When the MD is loaded into a player, theshutter on the cartridge is opened and the disc is ready to be played.Y For a recordable MD, because there is no need for a recording head and it is only necessary for a laser beam to bedirected at the underside of the disc, the shutter is located only on the back of the cartridge.Y For a playback/record magnet optic disc MD, because it is necessary for the recording head and the laser beam tobe able to access both sides of the disc, the shutter is located on both sides (upper shell and lower shell) of thecartridge.$ Basic Knowledge of MDT Definition of an MD and the types of MDsY MD stands for mini disc.Y Similar to a music CD, an MD is also a small disc capable of recording and playing back digital sound.Y There are 2 types of MDs, a optical disc for playback-only MD and a magnet optic disc for recordable MD that iscapable of both recording and playback.Y A playback-only MD is merely a smaller-diameter version of a CD. Just like a CD, the signals are read by lightstriking pits on the surface of the disc.Y With a magnet optic disc MD(Recordable MD) that is capable of both recording and playback, recording is per-formed by a vertical magnetization system in which a magnetic thin film on the surface of the disc is heated by alaser beam, and magnetism is applied in accordance with the data (audio signal) being recorded.Y When a recordable MD is played back, a laser beam weaker than that used during recording strikes the disc andis reflected back, and the reflected light is twisted (polarized) in accordance with whether the magnetized directionis upward or downward, causing the reflected light to rotate very slightly clockwise or counterclockwise. Thosesubtle differences in the reflected light are picked up by two light-receiving elements and detected as either a 1 ora 0 by reading whether there is electrical current or no electrical current.Y If an MD were recorded in the same way as a CD, it would only have about 15 minutes of recording time. However,by using a new signal compression technology called ATRAC that was specifically developed for MDs, the signalsare compressed to approximately one-fifth, making it possible to record for an extended time of 74 minutes, thesame as with a CD. (Blank MDs are currently marketed in two recording times, 74 minutes and 60 minutes.)Y Although MDs were originally developed for use in recording and playing back music, in July 1993 the MD datastandard was established. By using an MD data+music player, MDs can be used as external memory storagemedia for computers, and a single MD has a storage capacity of 140 MB, equivalent to about 100 floppy discs.U What is an MD?U Two types of MDsU Playback-only MD is sameas a CD.U Recordable MD usesmagnet optic recording.U Playback of a RecordableMDU 74-minute recording timeU Can also be used on acomputer.T Construction of an MDMD disc formRadioFans.CN 收音机爱 好者资料库SJ-MD100 3 D Recording on a magnet optic discU Can be recorded and playedback repeatedly.U Recording principleU Vertical magnetizationsystemU Number of recordingspossibleY By using a magnet optic disc, digital signals can be recorded and played back over and over again.Y To record on a magnet optic disc, a laser beams momentarily heats pin spots on the magnetic film on the back ofthe disc and a magnetic field is applied from the other side of the disc. Thus, both sides of the disc must beaccessed in order to record.Y To explain the recording principle, we will assume that the directions of the magnetism on an unrecorded disc areall facing downward (south-north = 0 0 0 0 .). (Actually on an unrecorded disc the directions are random.)Y Thus, to record the signals 1 0 1 1 0 1 0, the direction of the magnetism at the locations where 1 is to berecorded must be changed to face upward (north-south). Because the magnetic film is strongly magnetic, once adownward-facing magnetism is recorded, it is not easy to change it to an upward-facing magnetism.Y By directing a laser beam at the magnetic film, the temperature of the location that the laser beam strikes rises tothe Curie temperature (recordable MD; about 180pC), eliminating the magnetic force (retention force). (Becausethe magnetic film is strongly magnetic, similar to a permanent magnet, once it is magnetized it has a strongretention force. In order to eliminate that retention force, it is irradiated with a laser beam so that the temperaturerises to the Curie temperature.)Y After the magnetism of the specific location is eliminated, an external magnetic field with an upward direction(north-south) is applied, thus changing the direction of the magnetism at that location to face upward (north-south).Y Conversely, if a downward-facing (south-north) external magnetic field is applied, the direction of the magnetism atthat location is changed to face downward (south-north).Y Then, when the disc rotates and the location which has been changed to upward-facing magnetism leaves thelaser spot, the temperature of the magnetic film drops, and the upward-facing magnetism recorded at that locationis retained.Y In this way, digital signals of 1 (upward-facing magnetism) and 0 (downward-facing magnetism) are recordedon the tracks on the disc.Y With a conventional magnetic recording tape, the magnetic material is magnetized parallel (horizontal) to thesurface of the tape. A magnet optic disc, however, uses a vertical magnetization system in which the magneticpoles are recorded perpendicular (vertical) to the disc surface. Because the magnetism is recorded verticallyrather than horizontally, much more data can be recorded in a smaller area.Y A magnet optic disc can be recorded more than 1 million times, so it can virtually last forever.w w w w w w w w w w w w w w wSiw w w w w w w w w w w w w w wNOnly locations struck by apowerful laser beam(reach the Curie temperature)lose their magnetismretention force.BAssuming that the directions ofthe magnetism on the unrecordeddisc are all facing downward(they may also all face upward). ADisk rotation directionDisk rotationdirectionLaser spotiw w w q w t w w q q q w w qiw w w w w t w w w w w w wNAn external magnetic field is applied to the demagnetized location, creating upword-facingmagnetism.CRecorded signals.Directions of magnetism differaccording to whether a 1 ora 0 digital signal is recorded.DDisk rotation directionDisk rotationdirectionLaser spotS0 0 0 1 0 1 0 0 1 1 1 0 0 1BACDUpword : 1Downword : 0Surface of the disk is a magnetic thin film made of terbium-cobalt alloy.HeatedExternal magnetic field is applied.Magnet optic disc recording principleVertical magnetizationHorizontal magnetizationSJ-MD100 4 Y Because the signals on a magnet optic disc are recorded vertically as north-south and south-north magnetism, thenorth and south magnetic poles appear on the surface of the discs magnetic film. These signals are played backutilizing a phenomenon called the Kerr effect which occurs when a weak laser beam strikes the magnetic poles.Y Light has wave vibration directions called planes of polarization. (Polarization refers to a light wave whichvibrates only in a fixed direction.)Y With normal light, because the wave vibration directions are all mixed, no planes of polarization appear.Y Because a laser beam is artificially generated light, it is possible to align the planes of polarization.Y When a laser beam strikes something that has a magnetic field, the direction of the plane of polarization of thereflected light varies very slightly in accordance with whether the magnetism is north polarity or south polarity.When playing back a magnet optic disc MD, these slight changes in the direction of the plane of polarization areread.Y To further explain the principle used to read the signals recorded on a magnet optic disc, first a laser beam isdirected at the disc. If the direction of the magnetism recorded on the disc is upward (north polarity), the plane ofpolarization of the light reflected from the disc rotates very slightly clockwise as a result of the Kerr effect. Conversely,if the direction of the magnetism is downward (south polarity), the plane of polarization rotates very slightlycounterclockwise.Y When the reflected laser light is passed through a Wollaston prism, the light is distributed to photo detector 1 if thedirection of rotation is clockwise or to photo detector 2 if the direction of rotation is counterclockwise.Y The light striking the two light receiving elements is converted into electrical current and a subtraction is performed.If the result of A-B is plus, a 1 is detected, and if the result of A-B is minus, a 0 is detected.Y An MD player is compatible with both optical recording and magnetic recording, changing the reading system inaccordance with the type of disc that is loaded.D Playback of a recordable MDU Playback of a recordableMDU Reading of magnetic signalsChanges in the polarization axisdue to the Kerr effectPlayback of recordable MDSJ-MD100 5 Y The signals recorded on an MD are rewritten using a new process called “magnetic field modulation overwriting”*.Y In this process, a laser beam spot of about 5 mW is focused on the location on the disc to be rewritten, heating thatlocation to the Curie temperature (180pC) and thus canceling the magnetization.Y At the same time, current flows to the optical pickup and to the magnetic head opposite it, between the two of whichthe disc is held, thus generating a magnetic field.Y When the disc revolves so the laser spot moves from the location to be rewritten, the temperature drops below theCurie temperature and the magnetic field generated by the magnetic head re-magnetizes that location.Y At this time, if the direction of the current flowing to the magnetic head is reversed in accordance with whether thedata being recorded is “1” or “0”, the direction of the magnetic field also changes between north and south, andaccordingly, the direction of the magnetization of the recording film changes between upward-facing and downward-facing. Thus, it is possible to directly magnetize the recording film on the disc in accordance with the “0” and “1”digital signals.Y Thus, the new recording data is overwritten regardless of the direction of the previously recorded magnetization,eliminating the need for an erasing head.Y This process is called “magnetic field modulation overwriting”.Y Because this “magnetic field modulation overwriting” makes it possible to directly overwrite the new signals on topof the old signals in a single process, re-recording on a MD is just as easy as with a magnetic tape, making the MDideally suited for use in personal audio equipment.D Rewriting action of a magnet optic discU MD rewriting processU No need for a erasing headMagnetic field modulation overwriting*Overwrite means to write new data while erasing the old data.SJ-MD100 6 Y With a disc, high-speed random access is possible, something which is not possible with a tape.Y The optical pickup moves quickly in the radial direction, thus directly accessing the start of each track.Y With an optical disc, which is capable of playback only, the addresses in the TOC (table of contents) in the lead-inarea are all read beforehand in order to access the start of each track.Y With a recordable MD, which is capable of both recording and playback, blank guide grooves, called “pre-grooves”,are formed around the entire surface of the disc at the production stage.Y As shown in the illustration below, the pre-grooves wobble very slightly in a regular pattern, and that curve is fine-modulated (at intervals of 13.3 ms) to record beforehand the addresses of the continuous time data.Y Technically speaking, the pre-grooves in the disc is not perfect spiral but is wobble with : a typical amplitude of 30 nm. a spatial period of 54 to 64 m.When this wobble is locked to a frequency of 22.05 kHz, the velocity of the disc should be in the range of 1.2 to 1.4 m/s.Y In this way, even if the MD is blank, because the addresses are already recorded around the entire circumferenceof the disc, when the MD is recorded, those addresses are read in order to control the movement of the