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Harman kardon 635 freezes up when turned on - Audio & Video Receivers

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  • Arts52 Aug 11, 2008

    My AVR 635 freezes intermittly. To restart I have to use the manual on/off ( round ) switch None of the controls will work when in the freeze mode

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You must clean the lens you must use very little pressure. Take a cotton swab and barely moisten it with plain, non-scented, or oily type alcohol. In a swirling motion, very gently rub the lens until you’ve covered it entirely. DVD chassis, you can plug in the unit and check if this helped the player to "see" again. Most of the time you can check as is, though on the combo units you're going to have to slide the chassis assembly all the way back into the cabinet to get it to work because the cables are often too short. If this didn’t fix the problem, please read on.
Other things to check
If the cleaning didn’t help, don’t despair just yet. You can see if there’s a problem elsewhere in the unit by using a few simple tricks and tips.
First thing you want to see if the unit’s laser is in good working order. This method isn’t foolproof, but most of the time works admirably. When you insert a disc, see if you can look up underneath where the disc sits on the turntable. Observe the laser lens going up and down. If the lens is trying to focus, that’s good! After a few seconds of the lens trying to focus, the platter should start to spin. On almost every CD/DVD unit I've encountered, the unit won't spin unless the laser has properly focused on the surface of the disc.
f the unit spins up and and then shuts down, you should check and make sure the laser pick-up assembly slider mechanism is working without any obstructions and that the small chrome rail that it slides on is slightly greased. Don’t go overboard with the grease though, as too much can cause all sorts of problems.
The slider mechanism, depending on the age of the unit and the manufacturer, consists of the small chrome rail, a drive motor, a small gear assembly, and (in some units) a small belt that drives the slider unit via the motor. This small belt causes all sorts of problems. If the belt is broken or slipping, it can cause skipping, dropouts, or simply no start up at all. Also, if the belt breaks in the middle of the disc, the drive mechanism gets hair or dirt wrapped up into the gears, or the pick-up assembly doesn’t return to the start position (called home), the unit will (99% of the time) refuse to release the disc, causing it to become stuck inside the unit. There’s a little micro or leaf type switch located at home position that sometimes gets dirty or breaks and, causing this problem also.
If the disc starts to spin slowly and doesn’t come up to speed, the spindle motor that’s attached to the turntable platter is a common problem. There could also be a problem with the spindle motor driver controller IC or the power supply regulator that supplies voltage to the driver IC. If the disc starts to spin and then spins really fast, or stops and starts to spin backwards, your problem is the laser pick-up assembly or the servo control circuit.
Also, in a DVD/CD player there are many complaints where the disc gets stuck inside of the unit. This could be as described earlier, but there’s also what’s called a drawer/disc tray opener and closer mechanism to contend with. On many models, old and new alike, there’s a small belt that goes bad and wont let the tray open. You can usually put your ear very close to the front of the unit and, if this is happening, hear the motor spinning when you press the eject button. Another cause is the nylon gears, which can get jammed up with dirt and dust. Also, in other cases, you could have a motor problem, or the driver IC could be at fault. If you suspect that the motor is at fault, simply measure the voltage on the tray motor while pressing on the eject button. If the voltage comes up between 6 to 12 volts, depending on the manufacturer, then the motor needs to be replaced.
Alignments
If you continue to have problems after cleaning and checking the other things listed above, you may have a problem with the player's alignment. Of course, one of the problems you'll face checking alignments on a DVD/CD player is that you’re going to need to use an oscilloscope on most of them. If you have the proper tools and equipment, the first thing to look at is the RF pattern of the unit while its playing. It should be a sharp and clear pattern. If it's dull and smeared, then the laser could be weak.
Also, in these units are very critical alignments called the focus/tracking gains and offsets. When these alignments are off, it can often cause intermittent troubles. As the unit ages and parts change value, so do these alignments, and will need to be checked. In my time as service technician repairing DVD/CD players, 65% of the laser pick-up assembles I have tested were good and only needed a small adjustment. Today's technology makes it unfeasible for a shop to hook up a DVD/CD player, and even some recorders, to their equipment and make these adjustments because of the cost involved.

Posted on Jul 16, 2008

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