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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: CDRW does not read cds
Date: Fri, 27 Sep 2002 00:44:01 GMT
NNTP-Posting-Date: Thu, 26 Sep 2002 17:44:01 PDT
> Chuck Simmons wrote in message news:<3D926F44.A8786603@webaccess.net>...
> > "N. Thornton" wrote:
> > >
> > > firstname.lastname@example.org (email@example.com) wrote in message news:...
> > > > Hello,
> > > >
> > > > I have a panasonic (matshita/matsushita) CDRW , model CW-7585, that
> > > > was working fine on winXP Pro and Roxio Easy cd creator 5 platinum.
> > > >
> > > > Since yesterday it won't regognize cd's blanks or not. I opened it to
> > > > see if I could fix it using the extremely helpful instructions at
> > > > http://www.repairfaq.org/REPAIR/F_cdfaq.html. This is what I found:
> > > > Whenever I close the tray, (with/without a cd in it), the pickup moves
> > > > back and forth on the rack, positions at a specific location and then
> > > > stops. Then nothing happens. (Normally, the cd should start spinning).
> > > > About the laser, I could not see any red spots in a dark room,
> > > > whenever I closed the tray (with/without a cd in). Maybe the absence
> > > > of a cd did not power on the laser, and its appearance covered the
> > > > laser beam.
> > >
> > >
> > > Stop. You will permanently damage your eyesight like this. Do not play
> > > like this with cdrom lasers, nor cdrw lasers. Read up on it if you
> > > doubt me. It doesn't sound like youre taking the necessary precautions
> > > while working with a dangerous laser.
> > Don't blow this completely out of proportion. The CD read power we use
> > in my lab is between 500 microwatts and one milliwatt. It is best not to
> > look directly into the lens but there is no particular problem with
> > scattered light. I have to operate CD and DVD devices open in order to
> > make measurements including optical power output. Write power is more
> > problematic and eye protection should be used when measuring write
> > power.
> > > If the pickup moves but the spindle doesnt turn, the laser focus is
> > > not the issue. Possibles are the sensor not detecting the CD is
> > > present, or spindle motor is dead, or its drive cct. There are many
> > > other possibles of course.
> > Many CD and DVD devices use focus to decide if there is a disk inserted.
> > There is no other sensor in most. If a focus region cannot be found, the
> > drive assumes there is no disk. A CD drive can actually focus and track
> > without spinning the disk. Focusing on a stopped disk is useful but
> > tracking vibrations at one spot is a little futile. DVDROM can focus on
> > a stopped disk but cannot track. Anyway, if the lens does not do a
> > couple of "pushups" when the drive is turned on, it is probably not
> > bothering to look for a disk. The sledge moving to the ID at power up
> > and "tray open" is a feature. If the sledge is not at the ID, in many
> > units the tray interferes with the sledge when it opens or closes.
> > Moreover, the spiral on CDs and on the first layer of a DVD is always
> > outward so the drive must start at the ID.
> If I got this well, this poster is suggesting that the fault is at the
> focus mechanism? If so, what are the possible (SAFE) solutions to it?
> I suspect that I'm better off buying a new CDRW.
There are a number of possible faults. A drive can detect that it can't
spin. It can detect focus failure and it can detect tracking failure
once focus is established.
However, some simple things to check. There are usually two switches
(often in the same plastic housing) to sense tray open/closed. If the
drive cannot get a tray closed signal due to a faulty switch, it won't
try to do anything. The circuit board sometimes has maked teat points.
Verify that +5, +12 and +3.3 (if used) are OK on the board itself.
Sometimes there is a focus drive test point marked in various ways. It
will typically go to a chip made by Rohm which has power tabs on it
(there may be up to three Rohm power IC's. If the input signal to the
Rohm chip focus pin is ramping up and down but the lens does not move,
the Rohm chip is bad or the focus VCM is burned out. Focus and tracking
VCM resistances can be measured with the power off. These should be
about 4 to 10 ohms (usually close to 7 ohms in units I see). An open
focus VCM is fatal.
Anyway, look for the tray open/closed switch if your drive is so equiped
(most are). If this has failed, the problem is simple to correct.
Problems on the optical unit you cannot correct. Note that the optical
unit may be VERY ESD sensitive. Do not disconnect the flex from the main
board unless you are very well practiced with ESD procedures.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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