I've been given a radio/cassette/cd player with a faulty CD portion to
play with.

The CD spindle does not spin, but the motor operates if given 4+ volts
from a battery (and draws a variable current depending on mechanical load).

The laser actuators appear to work, because they attempt to hunt for a CD
to read. What I am not clear about is whether the focus process can work
with a stationary CD.

I consulted http://www.repairfaq.org/REPAIR/F_cdfaq*.html which suggests
that if the spindle does not start this may because of failure to focus,
implying the answer to my question is "yes"; but how?

Reading the specification for the "RF Amp + SSP" chip (KA9220C) does not
help me much either. However it does say "The KA9220C is designed for 3-
spot type optical pick-up assembly. ... The photo detector A,B, C and D
detect audio modulation signal on the disc and generate focus error
signal." That suggests to me that the disc needs to be rotating for focus
to happen. But if the above answer were "no" we would have a Catch-22
situation!

Can anyone explain, please?

Mike.

"Mike" wrote in message
o.uk...
I've been given a radio/cassette/cd player with a faulty CD portion to
play with.

The CD spindle does not spin, but the motor operates if given 4+ volts
from a battery (and draws a variable current depending on mechanical
load).

The laser actuators appear to work, because they attempt to hunt for a CD
to read. What I am not clear about is whether the focus process can work
with a stationary CD.

I consulted http://www.repairfaq.org/REPAIR/F_cdfaq*.html which suggests
that if the spindle does not start this may because of failure to focus,
implying the answer to my question is "yes"; but how?

Reading the specification for the "RF Amp + SSP" chip (KA9220C) does not
help me much either. However it does say "The KA9220C is designed for 3-
spot type optical pick-up assembly. ... The photo detector A,B, C and D
detect audio modulation signal on the disc and generate focus error
signal." That suggests to me that the disc needs to be rotating for focus
to happen. But if the above answer were "no" we would have a Catch-22
situation!

Can anyone explain, please?

Mike.


It is perfectly normal for the spindle servo not to be turned on until the
laser has obtained focus. When the spot is out of focus at the disc surface,
it will be eliptical, so the reflected beam will not illuminate all four
central pickup diodes equally (ABCD). The focus servo will move the lens
until this situation is corrected, indicating that the spot is now properly
round and in focus. The spindle motor is started up at this time. The
tracking servo is turned on once the disc is rotating (roughly the right
speed but not yet servo-locked), and makes use of the two other beams which
run equally either side of the 'groove'. If the central beam is off to
either side, the two side beams will be off position also, illuminating the
E-F pickup diodes unevenly. The tracking servo bends the lens to one side or
the other to correct this and keep the central beam running right over the
groove. The spindle servo is turned on as soon as valid data is being
recovered. The data recovery rate is used to lock the spindle servo to
control the rotational speed of the disc. This is constantly altering as the
disc plays. As the laser moves to the outer edge of the disc, the angular
velocity changes, so the disc is progressively slowed by the servo to
maintain a constant data rate.

If you want to get yourself a real in-depth understanding of the subject,
have a read of

https://books.google.co.uk/books?id=...tems& f=false

Not sure how the post will cope with a link that long, but I'm sure that you
will work it out :-)

How the beams within the optical block are used to obtain the various servo
locking signals is explained around about page 46 or so.

If focus is not obtained during the initial attempts - which are usually
three and bust - some players will 'kick' the disc to rotate it a little so
that a different disc area is exposed to the 'hunting' beam. This is in case
the disc is dirty or damaged at the initial try-out point. Again, this is
usually a 'three and bust' sequence. Some players do spin the disc
immediately the laser has checked that it is home, and focus is attempted on
the rotating disc. This is not common, however, as it introduces another
potential error term for the focus servo to cope with whilst trying to lock
in the first place, if the disc is warped or the turntable is not flat. Far
better that focus is obtained on a stationary disc.

If you are able, look under the disc and watch the lens. It should move up
and down just once and stop at some roughly midway position, indicating that
focus has been obtained. The FOK signal within the player will be asserted
at this time. If the lens moves up and down several - probably three - times
and then stops, then the laser did not obtain focus. By far the most
common - although not the only - reason for this is a defective laser. This
can be because it is simply worn out, or because of dust / film on the
surface of the lens, or dust / film on the critical-angle mirror or pickup
diode array inside the optical chamber. If the lens surface is clean, you
can try holding the lens gently to one side with a scalpel tip, and using an
air duster to blast a shot of air down the gap. Sometimes works ...

Most of the common lasers - Sony KSS series, Sanyo SPF101 series etc, are
incredibly cheap now, so usually worth a punt if you suspect a bad laser.
Most modern players are fully self-adjusting for servo gain and balance etc,
so a replacement laser job is pretty much just a case of 'drop it in'. If
the player does have adjustments, these are extremely easy to carry out with
a scope on the RF test point, or in the absence of a scope, are nearly as
easy to adjust with the benefit of a scratched disc and the mk 1 ear-'ole
.... :-)

If you have never replaced a laser, and end up giving it a go, you should
note that there is a blob of solder across a pair of shorting points on the
back of the little pcb on the laser. This protects the laser diode from
static damage when it is not connected to anything, and needs to be removed
when the laser is installed.

Arfa

Mike wrote:

I've been given a radio/cassette/cd player with a faulty CD portion to
play with.

The CD spindle does not spin, but the motor operates if given 4+ volts
from a battery (and draws a variable current depending on mechanical load).

The laser actuators appear to work, because they attempt to hunt for a CD
to read. What I am not clear about is whether the focus process can work
with a stationary CD.


** All the CD mechanisms I can recall seek focus before spinning the disk.

The most common failure seen in budget CD mechanisms is a weak or dead laser diode - which would produce the scenario you describe.



.... Phil

On Friday, January 9, 2015 at 12:45:52 AM UTC-5, Phil Allison wrote:
Mike wrote:

I've been given a radio/cassette/cd player with a faulty CD portion to
play with.

The CD spindle does not spin, but the motor operates if given 4+ volts
from a battery (and draws a variable current depending on mechanical load).

The laser actuators appear to work, because they attempt to hunt for a CD
to read. What I am not clear about is whether the focus process can work
with a stationary CD.


** All the CD mechanisms I can recall seek focus before spinning the disk.

The most common failure seen in budget CD mechanisms is a weak or dead laser diode - which would produce the scenario you describe.



... Phil

Or dirty.

Also, there is the possibility of a bad motor driver. This is not always an IC. It oculd be just a ocuple of transistors. If the spindle motor starts pulling too much current it can blow the driver. If in doubt, follow it back to whatever drives the motor to see if it is getitng dsrive but not driving. In that case the spindle motor might be bad.

The circuit is usually simple as hell. It is off when the buffer is almost full and on when the buffer is almost empty. And a transistor maybe for braking, if it even has that it usually just shorts out the motor so to load it and stop the disc. They don't use a negative voltage usually they just calculate the mass of the disk and with the motor loaded by the short it must stop ithin a certain time.

You say it is a combo unit ? Expect the absolute cheapest of circuitry. In fact if it has a pop up door instead of a drawer it probably has no braking and just has one transistor to drive the motor, on or off. Might even be a DTC something because the current is low.

Or supposed to be.

If you can get a print and find the FOK line and check it that is fine, but if whatever drives that motor is not told to turn on you can pretty much assume you don't have it.

I would clean the laser. what's more if you clean the laser and it starts working, tap on it with a screwdriver handle or something and see if it skips easily. then you got a weak laser. It will work for a time, BUT it is regulated so it will not last.

If you decide to tweak up the laser power ith that little pot, remember it is not going to last long and probably will still skip easily until it fails.

It is nice practice probaably fixing those thihgs but you are not goiung to make a fortune at it. Also, in some cases you can get the whole CD drive for about the cost of the laser. (I had a bad new one once and had to frankenstein the damn thing between parts from the new and old because the job had to go out, piece of ****)

On Thu, 08 Jan 2015 23:27:40 -0800, jurb6006 wrote:

Also, there is the possibility of a bad motor driver. This is not always
an IC. It oculd be just a ocuple of transistors. If the spindle motor
starts pulling too much current it can blow the driver. If in doubt,
follow it back to whatever drives the motor to see if it is getitng
dsrive but not driving. In that case the spindle motor might be bad.

The circuit is usually simple as hell. It is off when the buffer is
almost full and on when the buffer is almost empty. And a transistor
maybe for braking, if it even has that it usually just shorts out the
motor so to load it and stop the disc. They don't use a negative voltage
usually they just calculate the mass of the disk and with the motor
loaded by the short it must stop ithin a certain time.

You say it is a combo unit ? Expect the absolute cheapest of circuitry.
In fact if it has a pop up door instead of a drawer it probably has no
braking and just has one transistor to drive the motor, on or off. Might
even be a DTC something because the current is low.

Or supposed to be.

If you can get a print and find the FOK line and check it that is fine,
but if whatever drives that motor is not told to turn on you can pretty
much assume you don't have it.

I would clean the laser. what's more if you clean the laser and it
starts working, tap on it with a screwdriver handle or something and see
if it skips easily. then you got a weak laser. It will work for a time,
BUT it is regulated so it will not last.

If you decide to tweak up the laser power ith that little pot, remember
it is not going to last long and probably will still skip easily until
it fails.

It is nice practice probaably fixing those thihgs but you are not goiung
to make a fortune at it. Also, in some cases you can get the whole CD
drive for about the cost of the laser. (I had a bad new one once and had
to frankenstein the damn thing between parts from the new and old
because the job had to go out, piece of ****)

Thanks very much to all three of you for your comprehensive answers.

The unit is an Alba CX500L which is a budget brand and I haven't been able
to find any schematics or service manual. So I have left the four tweaking
pots on the PCB strictly alone! They are marked only with schematic IDs.
However the PCB does have numerous test points marked so I may play a bit
more... Also the actuator and spindle motor drivers are combined in IC
KA9259D and I have a specification sheet for that.

This is merely a learning hobby exercise. As soon as it gets too boring
the unit will get junked; I am unlikely to spend any money on it!

Mike.

On Thu, 08 Jan 2015 16:55:33 -0600, Mike wrote:

I've been given a radio/cassette/cd player with a faulty CD portion to
play with.

The CD spindle does not spin, but the motor operates if given 4+ volts
from a battery (and draws a variable current depending on mechanical load).

The laser actuators appear to work, because they attempt to hunt for a CD
to read. What I am not clear about is whether the focus process can work
with a stationary CD.

I consulted http://www.repairfaq.org/REPAIR/F_cdfaq*.html which suggests
that if the spindle does not start this may because of failure to focus,
implying the answer to my question is "yes"; but how?

Reading the specification for the "RF Amp + SSP" chip (KA9220C) does not
help me much either. However it does say "The KA9220C is designed for 3-
spot type optical pick-up assembly. ... The photo detector A,B, C and D
detect audio modulation signal on the disc and generate focus error
signal." That suggests to me that the disc needs to be rotating for focus
to happen. But if the above answer were "no" we would have a Catch-22
situation!

Can anyone explain, please?

Mike.

I've been out of the consumer electronics service business for 15
years so this comment may be off base. Back then cheap cd spindle
motors would begin turning at 3 volts not 4. Have you blasted the
brushes with contact cleaner, spun the motor at a higher voltage for a
few minutes, and cleaned and lubricated the bearings? When Pioneer cd
player motors went bad, spinning the disc by hand would start them
playing. If this works, you'll know the motor is bad. Chuck

I've been out of the consumer electronics service business for 15
years so this comment may be off base. Back then cheap cd spindle
motors would begin turning at 3 volts not 4. Have you blasted the
brushes with contact cleaner, spun the motor at a higher voltage for a
few minutes, and cleaned and lubricated the bearings? When Pioneer cd
player motors went bad, spinning the disc by hand would start them
playing. If this works, you'll know the motor is bad. Chuck


When Pioneers had a bad spindle motor, the disc still used to at least try
to turn, and it squealed like a stuck pig. Although other players tend not
to squeal like this, bad spindle motors are still common. On most players,
the disc will either rotate very slowly, or will rotate at a
'reasonable-looking' speed, but never actually reach a 'working' speed. It
is fairly rare for the motor not to start at all. The spindle motors will in
fact run at way less than 3 volts, as will the sled motors. The standard
test recommended by Pioneer was to connect the motor across an analogue
multi-meter set to its low ohms range. On this range, the impedance of the
meter was low enough that the internal 1.5 v battery could supply enough
current to run the motor. As well as running the motor, it also gave you an
indication of its 'resistance', which should be above 10 ohms. You could see
this figure climb from a few ohms when the motor was stationary, to over 10
ohms as the speed picked up, and back EMF started to contribute a term to
the meter reading.

You are quite right about squibbing switch cleaner in through the small
holes in the back-plate, and then 'blasting' the motor with excess voltage.
I do this with four or five short blasts of 12 volts first in one direction,
then the other. As you say, this is just a check though, and if the motor
runs and passes the 'meter' test afterward, it should still be replaced, as
it won't last long ...

Interesting that you used to employ this exact technique when you were in
the trade - presumably in the U.S. ? I first published it in a UK trade
magazine many years ago. Just goes to show that great minds think alike, for
you to have come up with it as well ! :-)

Arfa

On Sat, 10 Jan 2015 00:48:38 -0000, "Arfa Daily"
wrote:




I've been out of the consumer electronics service business for 15
years so this comment may be off base. Back then cheap cd spindle
motors would begin turning at 3 volts not 4. Have you blasted the
brushes with contact cleaner, spun the motor at a higher voltage for a
few minutes, and cleaned and lubricated the bearings? When Pioneer cd
player motors went bad, spinning the disc by hand would start them
playing. If this works, you'll know the motor is bad. Chuck


When Pioneers had a bad spindle motor, the disc still used to at least try
to turn, and it squealed like a stuck pig. Although other players tend not
to squeal like this, bad spindle motors are still common. On most players,
the disc will either rotate very slowly, or will rotate at a
'reasonable-looking' speed, but never actually reach a 'working' speed. It
is fairly rare for the motor not to start at all. The spindle motors will in
fact run at way less than 3 volts, as will the sled motors. The standard
test recommended by Pioneer was to connect the motor across an analogue
multi-meter set to its low ohms range. On this range, the impedance of the
meter was low enough that the internal 1.5 v battery could supply enough
current to run the motor. As well as running the motor, it also gave you an
indication of its 'resistance', which should be above 10 ohms. You could see
this figure climb from a few ohms when the motor was stationary, to over 10
ohms as the speed picked up, and back EMF started to contribute a term to
the meter reading.

You are quite right about squibbing switch cleaner in through the small
holes in the back-plate, and then 'blasting' the motor with excess voltage.
I do this with four or five short blasts of 12 volts first in one direction,
then the other. As you say, this is just a check though, and if the motor
runs and passes the 'meter' test afterward, it should still be replaced, as
it won't last long ...

Interesting that you used to employ this exact technique when you were in
the trade - presumably in the U.S. ? I first published it in a UK trade
magazine many years ago. Just goes to show that great minds think alike, for
you to have come up with it as well ! :-)

Arfa


Yes I'm in the U.S. I used to work at Best Buy's corporate
headquarters. I was pretty sure that the motors turned at less than 3
volts but I couldn't remember the exact voltage. It was likely that,
if it didn't turn until 4 volts, the motor was defective. Chuck