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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Hi,
Thanks to everyone for pointing me in the right direction with regards to the "initial" track position (inside) when you first insert a data CD. Another very important question: Is there a physical "stop" that stops the head (the head moves toward the center of the CD and "hits" a physical stop) at that "initial" track position, or is this done by "seeking" that "initial" track? Thanks in advance, Brad Before you type your password, credit card number, etc., be sure there is no active key logger (spyware) in your PC. |
#2
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There is always a limit switch/home position the laser sled returns to to
start reading. The start of the spiral track will be directly under the laser at that point. At the end of the disc there is ~2mins of 'stop code' so that when the laser finds itself here, it will know it must trigger 'stop' mode. CD writers are a little different since they can access an earlier porion of the disc for power calibration tests. AW "Brad" wrote in message ... Hi, Thanks to everyone for pointing me in the right direction with regards to the "initial" track position (inside) when you first insert a data CD. Another very important question: Is there a physical "stop" that stops the head (the head moves toward the center of the CD and "hits" a physical stop) at that "initial" track position, or is this done by "seeking" that "initial" track? Thanks in advance, Brad Before you type your password, credit card number, etc., be sure there is no active key logger (spyware) in your PC. |
#3
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"Cliff Top" writes:
There is always a limit switch/home position the laser sled returns to to start reading. The start of the spiral track will be directly under the laser at that point. At the end of the disc there is ~2mins of 'stop code' so that when the laser finds itself here, it will know it must trigger 'stop' mode. Note that the "start" of the spiral track is about 1.6 um wide. The limit switch gets you in the ball park. ![]() --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. CD writers are a little different since they can access an earlier porion of the disc for power calibration tests. AW "Brad" wrote in message ... Hi, Thanks to everyone for pointing me in the right direction with regards to the "initial" track position (inside) when you first insert a data CD. Another very important question: Is there a physical "stop" that stops the head (the head moves toward the center of the CD and "hits" a physical stop) at that "initial" track position, or is this done by "seeking" that "initial" track? Thanks in advance, Brad Before you type your password, credit card number, etc., be sure there is no active key logger (spyware) in your PC. |
#4
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Sam Goldwasser wrote:
"Cliff Top" writes: There is always a limit switch/home position the laser sled returns to to start reading. The start of the spiral track will be directly under the laser at that point. At the end of the disc there is ~2mins of 'stop code' so that when the laser finds itself here, it will know it must trigger 'stop' mode. Note that the "start" of the spiral track is about 1.6 um wide. The limit switch gets you in the ball park. ![]() My guess is the limit switch (or with the simple magnetic linear motor used, just sending it to one end and waiting until it can't possibly still be in transit) just gets you "inside" the starting track from which point you can start a search in a known direction. Figure the eccentricity of the disk's rotation is going to be many, many track widths wide, all the real alignment is done by error signals from reading the tracks themselves, it's not mechanically anywhere near that accurate in absolute position. I could be mistaken, but I think I've actually seen the control loops in simple players respond to an unreadable disk by doing a spindle speed search that includes going all the way down through stop and beyond, so they are spinning in the wrong direction! Could be wron about that, or it could be an artifact of a brushless motor drive circuit rather than the control loop though. |
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