new 1/13/2003
Looking for help diagnosing problem with cd changer in trunk on a 99 SHO.
Whenever I try to play a CD I get "bad CD" message on all 6 CD's. I know
the CD's are good and believe the problem is with the CD unit. Before I
spend 200.00 for a new changer does anyone know of something I should check
on first. Thanks for any help you may be able to provide.
Brad DeGroft
My CD player had a "No CD" problem about 2 years ago. I found a fix to this problem and my CD player has worked flawlessly for the last two years since the fix. I'm not sure that your problem will be the same since you get a "Bad CD" message, not a "NO CD" message but you may want to try it if you are game to open up the CD changer.
I have copied my original post from two years ago below. I also have photos illustrating the key CD player components pertaining to this fix if anyone is interested (the file is a few Mb due to the picture resolution).
My CD player has been acting up lately skipping disks positions in the magazine and reporting "no disk" when this happens. This problem was erratic and slowly became worse over time. Ejecting the magazine and pressing it back in would allow all the CD's to be recognized again albeit for a short time in some cases. This weekend I finally had time to take apart the CD unit to fix it.
What I found is that the jack screw mechanism, which aligns the player to each of the disks in the magazine, was misadjusted slightly. Once adjusting this, the player always recognizes all the disks in the magazine and I saved about $300 for a new CD player compatible with the head unit.
In the case of my unit when diagnosing the problem, I watched the CDs move half way into the mechanism only to return back to the magazine when the CD disk transport time exceeded the limit programmed into the control logic. If I tilted the whole unit on end to allow gravity to help the disk move into the mechanism, it worked correctly every time. This is how I determined that I had a traction problem with the rollers.
Description of Fix
The CD player mechanism moves back and forth on jackscrews to align itself with the position of the selected disk in the magazine. This alignment system has a rotating vane sensor with slots in it and a photo-sensor that counts the slots as the jackscrew rotates. The CD player uses this to determine the distance the mechanism must travel for each of the CD positions in the magazine. While the system knows the distance it must move from disk to disk, it doesn't know if it is properly aligned to the disk when it stops at each position. This must be manually adjusted. It appears that over time this adjustment can drift off if the vane sensor ever errors in counting the vane slots.
On the top of the CD player behind the plastic sliding cover is a lever that has a pointer that identifies the position of the mechanism. This pointer must be set to be exactly equidistant between the tick marks stamped into the housing (There are tick marks for each of the 6 positions but if you disconnect the player without the magazine inside, it will be sitting in the default 1st CD position). This can be accomplished by rotating the vane sensor by hand, which will manually move the mechanism to a new home position. Note that moving this by hand causes the worm gear on the little DC motor to jump the teeth on the jack screw gear so only do this enough to realign the mechanism.
While you have the unit apart, you should clean the disk transport rollers. This is accomplished with alcohol and small cloth. Greasy rollers equal slip and poor operation. These are two rubber-covered rollers that resemble two rolling pins. They are about 3 ½ inches long and small in diameter. Their purpose is to catch the CD between them as it is ejected from the magazine and to quickly move the CD into position over the CD drive hub. The roller with the rubberless gap in the middle is the free spinning idle roller while the other is the drive roller that does all the work. They are normally spread apart but they squeeze together with the disk in between and rotate when commanded to move one disk back into the magazine and the next from the magazine into the mechanism. If the magazine is out of position, the CD disk may press more against the idle roller and less against the drive roller due to the misalignment and cause the drive roller to loose traction and slip. This causes the disk to move slowly or hesitate. The mechanism is impatient and the control logic will conclude that no disk is in that position if any hesitation occurs. It remembers this once that happens and will no longer search that position for a CD until you eject the magazine.
The last part of the mechanism (for reference) is a disk eject finger that pokes into the CD magazine and pops the CD out for the rollers to catch. This finger engages one of 6 plastic pins that are built into the CD magazine that engage the white lever mechanisms you use to manually remove CDs from the magazine.
It is a good idea to wash your CDs or make sure they are free of grease and oils before inserting them into the unit. Over time all of this is transferred to the rubber rollers as they roll over the entire CD surface on both sides picking up whatever junk is there.
I have some pictures of the components mentioned above and can post if there
is interest.
Don R
Note the black plastic gear with the slots at the top - This is the vane sensor gear and it is mounted directly to the jackscrew that raises and lowers the mechanism. The DC drive motor is to the left of the gear and it has a worm gear that engages the vane sensor gear. The vane sensor gear must be rotated by hand to readjust the alignment.
This lever indicates the mechanism position. Note the alignment tick marks. The mechanism is currently in the first position and properly aligned.
Note the two long skinny rollers. The top one is the drive roller while the bottom one (partially visible just below it is the idle roller. These rollers are normally separated but this gap is closed under spring pressure when they operate. Note the small metal finger projecting out between the far end of the rollers. This is the disk eject finger. This finger moves in and out to eject a disk from the magazine.
Many thanks to Don for an excellent write up. As I gave up on the skipping problem two years ago and bought a 10 Disc that works flawlessly, I know that this will help lots of folks.
U.L.