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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
References: <3D926F44.A8786603@webaccess.net> <3D93A9C1.8F29D7EC@webaccess.net>
Date: Fri, 27 Sep 2002 23:06:26 GMT
NNTP-Posting-Date: Fri, 27 Sep 2002 16:06:26 PDT
> Chuck Simmons wrote in message news:<3D93A9C1.8F29D7EC@webaccess.net>...
> > "email@example.com" wrote:
> > >
> > > 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.
> > > > >
> > > > >
> > > >
> > > > > 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.
> > Chuck
> I appreciate your help. However, being a novice, I did not quite
> understand your tips. Maybe real **detailed** instructions, (if anyone
> has the time for it) would help.
> By the way, I have some more info on the subject: I managed to see a
> red spot on the lens (appearing after closing the tray). So that maybe
> an indication that the laser may work ok.
Did the lens move up and down while there was a red glow? (Best not to
look into the lens - view from the side.) Did the spindle turn?
I can't give really detailed instruction. I could tell you haow the team
I'm on does this stuff but that's no help because the drive you have
wasn't designed by us.
The laser is problematic. I can't even tell if a DVD laser is up to
power by eye let alone a CD laser. I have a power meter for that. If the
power is low, the device may refuse to operate. Note that the drive can
sense this condition.
If the lens moves but the spindle does not turn, the spindle driver may
be bad. The spindle driver is in one of the power chips with large tabs.
It is usually combined with some other power function(s). Can't help you
on spindle drivers. Rohm must have more than 10 different types - forget
that there are a couple of other makers.
If the spindle turns but the lens does not move, the focus driver or the
focus coil may be bad. The focus driver is in a chip with tabs (many
models of this turkey - it gets confusing - often Rohm). If the spindle
turns, there is an 0.5mm pitch flex connector for the optical unit flex.
It has a lot of pins (30 to 50 in the examples I have). The focus and
tracking coils are usually the four end pins at one end or the other.
The order of the pins varies. During initial power up, one pair of those
pins should have a voltage that ramps. If you can probe 0.5mm pitch pins
with a regular voltmeter or scope probe, I give you a lot of credit. I
usually short all kinds of things out when I try. If you find the
ramping but the lens does not move, the focus coil is burned out. You
can't fix that. The entire optical unit must be replaced.
Even if you can get a replacement optical unit, the unit may present
challenges. The type I currently use has a spring we call the "Oh Damn"
spring because when it flies across the room never to be seen again, the
only thing you can say is "Oh Damn."
... 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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