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.

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
  #1   Report Post  
Posted to sci.electronics.repair
Brad
 
Posts: n/a
Default "Initial" Track on CD Rom Disk (Physical Stop or "Seek")

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   Report Post  
Posted to sci.electronics.repair
Cliff Top
 
Posts: n/a
Default "Initial" Track on CD Rom Disk (Physical Stop or "Seek")

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   Report Post  
Posted to sci.electronics.repair
Sam Goldwasser
 
Posts: n/a
Default "Initial" Track on CD Rom Disk (Physical Stop or "Seek")

"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   Report Post  
Posted to sci.electronics.repair
 
Posts: n/a
Default "Initial" Track on CD Rom Disk (Physical Stop or "Seek")

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.

Reply
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules

Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
LG DVC6500 behaves like 'stop' button pressed with DVD HandyMan Electronics Repair 3 October 1st 05 07:29 PM
WANTED: PLANER Jim Woodworking 25 August 24th 05 01:21 AM
OT - 386 code Cliff Metalworking 40 January 24th 05 05:47 AM
safety question - many short cut-offs using a stop igor Woodworking 16 November 21st 04 02:17 AM


All times are GMT +1. The time now is 07:41 PM.

Powered by vBulletin® Copyright ©2000 - 2023, Jelsoft Enterprises Ltd.
Copyright 2004-2023 DIYbanter.
The comments are property of their posters.
 

About Us

"It's about DIY & home improvement"