Technics Audio CD Player - problem
David Longley
After about 6 months of not using the unit at all, I have
switched it on and although everything seems to work, when I put
a CD in, the display does not change and there's no sound.
I've opened it up, bloan on it to get rid of dust, and even
dusted down the laser head (small glass blob). No difference. Can
anyone suggest what the problem is and a solution (apart from
buying a new one!).
--
David Longley
Walt
There are a few things you can do in your case...
if you are a technician,
1) see if you have any moisture buildup on the bottom of the circuit
board. if you do resolder it (if you are lucky the moisture didn't
damage a chip) be extra careful that no leads on a surface mount chip
are bridged (soldered together).
2) you can clean the lens of the CD player with a Q-Tip and rubbing alcool
(both can be purchased at the local pharmacy).
3) get a service manual and check the alignments of the oscillator, focus gain
tracking gain.
4) check to see if the motor is getting the proper voltages to spin the CD. If not
then check the soldering on the motor drivers or see about the moisture that could
of damaged the IC.
if you are not a technician,
1) listen if the CD is spinning in the unit.
if so then you could have just some dust/dirt buildup on the lens. Bring
it in for servicing or take the cover off and clean the lens with alcohol VERY,VERY carefully.
Load disk and try again. If no moisture is in the machine and it was well stored then it
should work
if not then call for an estimate at a service center.
REMEMBER .... Call a service center that is authorized to repair your brand of CD player
because they will have all the latest schematics on your unit from the factory!!!
Other than the above info that is all a non-technician can and should do.
email me at rig...@wincom.net to tell me what happened...
Sam Goldwasser
> David Longley <Da...@longley.demon.co.uk> writes:
> > I have a problem with a Technics SL PJ44 Audio CD Player.
> >
> > After about 6 months of not using the unit at all, I have
> > switched it on and although everything seems to work, when I put
> > a CD in, the display does not change and there's no sound.
> >
> > I've opened it up, bloan on it to get rid of dust, and even
> > dusted down the laser head (small glass blob). No difference. Can
> > anyone suggest what the problem is and a solution (apart from
> > buying a new one!).
> > --
> > David Longley
> There are a few things you can do in your case...
> if you are a technician,
> 1) see if you have any moisture buildup on the bottom of the circuit
> board. if you do resolder it (if you are lucky the moisture didn't
> damage a chip) be extra careful that no leads on a surface mount chip
> are bridged (soldered together).
He didn't say it was stored in the bilge of a fishing tramp steamer!
Under normal conditions, these sorts of problems are very rare.
> 2) you can clean the lens of the CD player with a Q-Tip and rubbing alcool
> (both can be purchased at the local pharmacy).
This is alwasy good advice - just be gentle.
> 3) get a service manual and check the alignments of the oscillator, focus gain
> tracking gain.
These don't drift from non-use unless the adjustment pots develop
corrosion. Also, focus and tracking offset tend to more critical than
the gains.
> 4) check to see if the motor is getting the proper voltages to spin the CD. If not
> then check the soldering on the motor drivers or see about the moisture that could
> of damaged the IC.
Many other faults can cause the spindle motor not to turn - like lack of focus,
bad motor, faulty power.
My bet is on something mechanical - drawer not closing completely causing
disc to not be clamped properly, sled not resetting to inner limit, or a
dirty lens. Perhaps, dirty contacts on an internal connector.
Startup problems can be tackled in a systematic way - disc clamped, sled
resetting to inner limit, laser power, focus, tracking, spindle drive and PLL,
sled drive.
--- sam
Sam Goldwasser
> I have a problem with a Technics SL PJ44 Audio CD Player.
> After about 6 months of not using the unit at all, I have
> switched it on and although everything seems to work, when I put
> a CD in, the display does not change and there's no sound.
> I've opened it up, bloan on it to get rid of dust, and even
> dusted down the laser head (small glass blob). No difference. Can
> anyone suggest what the problem is and a solution (apart from
> buying a new one!).
On a unit that has not been used in a while, I would go with gummed
up lubrication or a worn belt. Confirm startup behavior and get back
to us.
CD Startup Problems:
-------------------
What it should do:
1. Door closes (or with portables, is closed manually) and CD is clamped to
spindle.
2. Interlock (if present, always in portables) engages. In others, there
may be an optical sensor or the laser pickup may act as its own disc
sensor.
3. Pickup resets to starting (index) location toward center of disc usually
found with limit switch or optical sensor.
4. For the following, refer to the diagram below of the photodetector
organization typical in units with a 'three beam pickup'. E and F will
be absent in units with a 'single beam pickup', though there may be
other segments. The four quadrant photodector is present in all systems.
+---+---+
---------_________ +---+ | A | B | +---+
Track---> | E | +---+---+ | F | ________
+---+ | C | D | +---+ ---------
+---+---+ Track--->
The main return beam is detected by the array, ABCD. The tracking beams
return to E and F. E is offset slightly off track on one side and F on
the other. Average signals from E and F will be equal when centered
on track.
4a. Laser is turned on and focus search routine is started to position lens at
correct vertical position. Once correct focus is achieved, focus servo is
activated to maintain it. Focus, which must be accurate to 1 um, operates
as follows: The optical path in the pickup includes a cylindrical lens
which causes the laser beam spot to be circular when correctly focussed but
elliptical otherwise with the major axis of the ellipse being offset 90
degrees depending on whether the lens is to close or too far (e.g.,
major axis of +45 degrees for too close and -45 degrees for too far).
Focus Error = (A+D)-(B+C) = 0 for correct focus since with the circular
spot, the outputs of all four quadrants will be equal.
4b. Disc starts spinning up to 500 rpm and Constant Linear Velocity (CLV) servo
is activated to maintain correct speed. CLV servo uses a PLL to lock
to clock transitions derived from data read off of disc. Data is derived
from A+B+C+D.
4c. Tracking servo is activated to maintain laser beam centered on track.
With 'three beam pickup', 2 additional laser spots are projected onto
the disc in front of and behind main beam. These are offset on each side
of the track just enough so that Tracking Error = E-F = 0 when centered.
With a 'single beam pickup', similar information is derived using only the
main beam since Tracking Error = (A+B)-(C+D) = 0 for correct tracking.
5. Disc index is read and displayed.
6. Unit shuts down awaiting command or goes into play mode depending on
how it was activated.
The steps listed as (4a,b,c) may or may not be performed concurrently.
If any of 1-5 fail, then the laser is turned off and the machine will
display some kind of error no disc message and return to idle mode, or in
the case of a changer, load the next disc and try again.
The following procedure is used when the disc is not recognized but the door
closes completely. Usually, after a few seconds, the machine gives up, or
in the case of a changer, loads the next disc.
First, double check the door closing/opening mechanism.
If the door does not close completely, then the disc may not be clamped
properly or other erratic problems may occur.
Once you have verified that this is ok, you need to determine:
That the lens is clean. In general, the lens should look shiny with a blue
tinge. Any scum or crud can degrade performance. If in doubt, use a
CD lens cleaning disc (if the CD spins), use a photographic air bulb to
blow any dust from the pickup, and/or clean with 91% medicinal or
pure isopropyl alcohol. Be gentle! Use a Q-tip (cotton swab) moistened
but not dripping with alcohol. Gently dry with a second Q-tip or lint free
cloth. You may have to remove the clamper and/or move the pickup by hand
to get at the lens. Don't force anything!
Verify that the pickup has reset itself to the inner (center) track of the
disc. If necessary manually move the pickup away from the center by
turning the appropriate pulley or gear, or in the case of a linear actuator
or rotary positioner (no gears or belts), just push the pickup gently and
observe the behavior when a disc is loaded. The pickup should move smoothly
toward the center, usually tripping a limit switch and stopping. If there is
no movement, then lubrication may be needed or the motor or drive circuitry
is faulty. Measure the voltage on the motor that moves the pickup. If there
is none or it is very low (under a volt or so), then there is a problem with
the motor or driver.
Determine if the machine attempts to focus. On portables, it is sufficient to
defeat the door interlock to get the operations associated with reading of the
disc index to begin (you may need to press play - this is model dependent).
In some component CD players, a disc actually has to be present to block an
optical sensor. You should see the lens moving smoothly up and down once or
twice about 2 mm. If a disc is in place, then the lens should quickly stop at
the appropriate focus position. Admittedly, observing the lens may be
difficult or impossible with the disc in place. Dentists are probably good at
this!
If the focus pattern is identical whether a disc is in place or not - i.e.,
it keeps up the search pattern and then gives up - verify that the laser
is being powered. In most cases, the types of laser diodes used in CD players
produce a very weak spurious red output although the main beam is infra red
(IR) and invisible. From a safe distance of at least six inches and 45 degrees
or more off to one side, you should be able to see this dim red light in a
darkened room while the unit is attempting to focus. If you see this, you can
assume that the laser is being powered though it is not a sure test for an
actual IR laser beam or proper optical power output. In most cases, however,
the red light indicates that the laser is working. An IR detector would
confirm at least that there is an IR emission. If there is no red light, then
either the laser diode is bad, it is not being powered, or the type of laser
diode used in your CD player does not produce this spurious red emission.
You can purchase an inexpensive IR detector card from an electronics
distributer or build one using a photodiode, a few resistors, a general
purpose small signal transistor, and an LED running off a 9 V battery.
This will also be useful for testing remote controls.
Once focus is established (and sometimes concurrent with this operation),
the spindle should begin to turn and quickly get up to 500 rpm. The speed
may be ramped up or controlled in some other search pattern since there is
no speed feedback until the data coming off of the disc is available.
A partially shorted motor will prevent the spindle from reaching 500 rpm
even though the disc will spin. Check the voltage on the spindle motor
when it starts the disc spinning. It should reach 2 volts or more. If less
than a volt but not zero, a partially shorted motor or weak driver is likely.
If zero at all times then there may be a bad driver or the machine may not
realize that focus was established and is not issuing the spindle motor
start command. 500 rpm - just over 8 revs. per second - can be estimated
by using a disc with a dramatic label or putting a piece of tape on the
side of the disc that is visible and watching it spin.
Once the disc reaches the correct speed, the speed control (Constant Linear
Velocity, CLV) and tracking servos will be activated and data wlll be read
off of the disc. Either of these could be faulty and/or misadjusted making
it impossible to access the disc index.
During the time that the disc is spinning and the player is attempting to
read the disc index, listen for that 'gritty' sound that CD players make
during normal operation. It is a byproduct of the focus and tracking servos
constantly adjusting lens position - the rapid movements of the lens produce
audible sound like a loudspeaker - and its presence is a good indication that
(1) the laser is working and (2) focus is being maintained.
On certain CD players, for example many Pioneer models, there is a TEST mode
which enables many of the individual functions such as focus and tracking
that are normally automatic to be manually enabled. This is a very
useful aid is diagnosis and in adjusting a machine from an unknown state
as would be the case if someone else twiddled every internal adjustment
they could find! (Also Pioneer TEST mode is discussed in the FAQ
below which may be of hellp).
Repair Notes are available at:
http://www.paranoia.com/~filipg
--- sam