Question about Sony MHC-991AV Shelf System
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Posted on Jan 02, 2017
Some possible causes:
a) dusty laser lens - cleaning it is the solution, you may use the lens cleaner disc (the one that uses liquid), this can be purchased in many shops. I prefer to clean the lens manually, using a cotton stick and some ethyl or isopropyl alcohol (DO NOT use acetone, benzene or similar strong solvents, these will ruin the lens).
b) dirty brush contacts inside the spindle motor (i repaired quite some CD players that had this kind of trouble). They cause the motor to spin with less power so the driver tries to compensate putting more power into the motor, which causes a feedback effect on focus (it may not work properly). The best solution for this is to replace the spindle motor (if you can find one), the second best solution is to clean the brushes and the commutator (that's what i usually do), but this is a pretty delicate and somewhat complicated procedure since you have to open up the motor, clean it and then put it back together in a correct way. I wouldn't recommend doing this unless there is absolutely no way to obtain a new motor (if you are truly interested in learning how to do it, post me a message, i'll explain it).
c) the main power switch has oxydized contacts, which means that the voltage on the primary of the power transformer is a bit lower, and, consequentially, all of the secondary voltages are lower, too. I know it may sound weird, but i had some players in which i cleaned the lens (on BOTH sides plus the mirror inside the laser), opened and cleaned all of the motors, but they would still not work correctly. Only after i've cleaned the contacts on the main power switch did they return to normal functioning. Obviously it's much easier to change the switch to solve this (if you have a spare one). You can check if the switch is the cause if you bypass it (you need to bring the mains voltage directly to the primary of the power transformer, but do it with caution as mains voltage can be LETHAL to you and your CD player - i don't recommend this either if you're not trained in electric safety).
These are just some of the possible causes. It may as well be that the real cause is something else, so don't take any of these for granted, they are just suggestions.
Anyway, i hope you can fix it (or at least have someone do it for you).
Good luck and best regards
Posted on Jul 18, 2009
All you can do is get a lens cleaner and hope that clears it up, otherwise you are looking at what might be an expensive replacement of the CD/lens/laser unit.
Posted on Dec 22, 2009
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Nov 28, 2013 | Sony Audio Players & Recorders
A malfunctioning stereo may least allow feature buttons to perform extractions of CDs. Depending on how the stereo was installed, the car would have to be powered on to attain stereo functionalities. Second, CDs have to be inserted with the readable media side facing the appropriate lenses to achieve results. A wrong insertion of the CD into stereo compartment may require forceful extraction. Observe the type of stereo to ascertain CD extraction also known as reset buttons. Usually a tiny area, the reset button allows inserting an object that forces the car stereo to eject stuck disks. Every mean to eject stereo disk have to be performed while the car is turned on to utilize the source of power. An unsuccessful attempt to dislodge CDs in stereo compartments would require auto electrician's consultation. An unsuccessful dislodge attempt usually requires acquiring a new stereo in replacement of the malfunction.
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