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Thread: CD no disc

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    Default CD no disc

    Hi all,
    Got one of those midi type stereo systems that wont read a CD.
    It's a Sanyo unit with a 3 cd changer.
    I haven't had much to do with this kind of fault before.
    The laser head moves, the disc turns a little then the error "No Disc" is displayed.
    I've cleaned the laser lens and put a drop of lube on the disc spin motor shaft.
    I've also replugged some cables.

    What should I look at next ?



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    The first step after the pickup assembly reaches the inner home position is the laser diode is turned on and a focus search is activated to determine whether a disc is present. You can see the red light if the LD is working (don't look straight into it). No red light = dead laser diode. There is an LD on command from the control electronics, fed to the PU assembly via a Flat Flex Cable. The FFC from the PU assembly to the PCB is often the culprit as it is continually subjected to movement and can fracture. Pioneer players were particularly subject to flex cable failure (I used to keep them in stock).
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    Thanks for that.
    Looks like the cable from the laser is some of that audio coax about 1.5mm diameter and running to the main board.
    Also individual wires grouped to another plug near the laser probably for motor control. That also goes to the main. No flat ribbon on this one.
    I'll put a meter over all of those.

    PS. Is the focus search mechanically operated ?...Meaning, would I see the lens move back and forth ?
    Last edited by loopyloo; 15-05-13 at 10:03 PM.

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    I can only get a really low angle view of the laser lens and can't see any red.
    Could it be infra red ?
    Last edited by loopyloo; 15-05-13 at 10:38 PM.

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    780 nm wavelength for CDs is at the end of the visible spectrum. I know the type of cable to which you refer; these rarely give any trouble. Sanyo tend to make their own laser PU assemblies whilst many others use the Sony KSS series. Look for a sticker on the PU assembly for a part number and a quick search will reveal its pin outs. The lens is driven axially and radially by a simple coil arrangement similar to a speaker voice coil. Basically you will see it move up and down during a focus search.

    Last edited by TVguy; 16-05-13 at 08:17 PM. Reason: error
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    Ok thanks I'll check up on it.

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    Hi Loopyloo

    The norm with cd/dvd players is the laser fires and gets a signal then tries to focus by spinning the disk to get data as to type of disk CD/DVD/Data then it loads the right prg to play the disk. So defeat the interlock and see if the laser turns on a red light from the lens (Do Not look straight at it) Then load a disk with the interlock defeated did the disk spin up quickly? No the spindle motor could be at fault. If the disk did not move it may be the laser or a pcb fault. Now you have to decide you time and cost of parts.

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    I managed to remove the round capture plate that sits on top of the disc. With that out of the way and no cd I could see the laser but no red operation.
    The spindle turn fairly quickly only a few turns with no cd, but slowly a couple of turns with the cd. Naturally the spindle would take more time to spin up with the weight of a cd to turn. I assumed the circuit would see no disc fairly quickly and just abort after it started the spin up.
    I did try to help it spin up with my finger but only managed to scratch the cd when the mech dropped out of the way and the cd spun to a stop on the platter.
    The cables from the laser to the mainboard tested ok.

    So, in order of operation, is the laser supposed to check for a cd before the cd spins, meaning it wouldn't bother spinning it at all if it didn't see a cd ?
    Last edited by loopyloo; 16-05-13 at 01:13 AM.

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    It is possible that it spins then turns on the laser.

    Can you see the lens move and does the laser travel back and forward a mil or 2 ?

    There is a small push switch that tells the micro that the laser is at the start position if you can try and wind the laser away from the center a 4 or 5 mil and see if it returns to the center when you load a disk.

    If not you possibly have a faulty micro or driver ic or a power supply problem.

    If moves back to the start and the lens moves i would say a dud laser assembly

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    Quote Originally Posted by loopyloo View Post
    Hi all,
    Got one of those midi type stereo systems that wont read a CD.
    It's a Sanyo unit with a 3 cd changer.
    I sorry I have to disagree with some coments above but a true CD player only uses an infra red laser(unless that has changed just lately).
    Also DVD/CD devices have infra red and red laser combos.

    Try viewing through it a digital camera before you assume a dead laser.

    780nm is normally not viewable by the humble human.
    Last edited by Uncle Fester; 16-05-13 at 02:51 PM.
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    True enough (my mistake) that 780 nm is in the infra red range, but I have been working on CD players since 1986 and definitely can see a red glow when the laser is on (as have my co-workers). It is only faint and I have never had to use a camera yet; I must be seeing some of the near IR range. I had training from Japanese engineers at Panasonic who pointed out this method of checking from an angle or using a piece of white paper held above the lens to see the spot.
    Last edited by TVguy; 16-05-13 at 09:29 PM.
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    I've seen plenty of Red Laser lights on CD players.

    AFAIK, the cd must spin upto a set speed, and then the laser has to read (i think), a TOC (Table of Contents), like a menu where everything is, to start to 'play/read' the whole CD.

    Sometimes the PU can be very slightly off, but if no TOC then it doesn't play/read.

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    ...and I have seen plenty in sole CD players that don't glow and work fine.

    Some might emit weak visible light in their back ground spectrum but this is not even evidence that it is lasing (or lasing enough) because monochromatic 780nm lasing on it's own is invisible.

    Also a dead DVD laser can still glow red.



    My first experience with IR laser diodes was 1978 when I worked in a lab in Germany that designed and manufactured attenuation meters for fibre optical cables. I still have a near IR 27 watt pulse laser diode from that time and it certainly doesn't glow red.
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    I tried placing white paper over it but saw nothing.
    Couldn't see the lens move.
    If I wind the laser trolley away, it returns to attempt a scan.
    And dang,,,I have known about the camera trick for years but for some reason I always forget to use it as a test.

    One place I worked at we used IR emitter/receivers a lot. My mate would make a tunnel around the emitter with his fingers and hold it right up to his eye. He'd say "yeah that ones working, see"?...No I couldn't see it. Conclusion is that the spectral sensitivity of the human eye must vary from person to person. Hmmmm...Does that mean that maybe some people can actually see ghosts ?
    Last edited by loopyloo; 17-05-13 at 04:01 PM.

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    you will find trim pots on back of pic up try marking it where it is and turning clockwise bit by bit till it read disc allso had them go dirty so just a turn ever way and back got them going

    I have bean a Sanyo service agent for ner on 30 years and the old Sanyo cd player with the Sony pic up did not glow red
    we used to use a inferred power meter to see the power of the laser only ever see the red glow on cd dvd pic ups that have 2 laser

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    Checked the laser with a camera and found it to light up steady orange after the laser has moved into position against the cd. (No cd for check).
    There are no trimpots.
    Also, just noticed that the laser does move like for a focus check.

    If it helps, the model of this unit is Sanyo DC-S350U.

    Loopyloo

    Last edited by loopyloo; 20-05-13 at 11:03 AM.

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    Wait. I found a trimpot.
    Will have to remove the back to get at it.

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    Trimpot adjustment didn't work.
    I'll give up on this one and hand it back tomorrow.

    Thanks anyway guys.

    Loopyloo
    Last edited by loopyloo; 20-05-13 at 11:58 AM.

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