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Old 7th February 2010, 10:36 AM   #1
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Default Compact Disc Motor and Turntable - Advices for Replace and Motor Service wanted

There are two kinds of disc motors: those that are suitable for disass'y (brushless in most cases) and those for "one way" use, not suitable for disass'y without destroy.
By today's cd/dvd mechanism in most cases the last mentioned are in use. Naturally the complete mechanism is renewed in case of a failure inside in disc motor. And if this mechanism no longer available (by older models very often to observe) an other solution than throwing away the complete compact disc player I wanted.

To make matters worse additional pressed turntable are to find in most cases instead such with set-screw for exactly hight adjust
I perform the remove of such pressed turntables and and re-press to a new motor device several times (mostly by Linn Karik), but this is a very unpleasant work. I want to know better solutions.

About post #16 #19 and #21 about
All Diyaudio Threads about not available Optical Pickup's from Sony's KSS-Series
you will find first ideas
But because the thread there is a complete other topic, I start this thread here.

It would be very interesting to know, which brands offers several motors suitable for complete disass'y (removable sinter bearing and removable sliding touch in case of not brushless versions).
If there are brushless versions for 1:1 exchange (same sizes, same arranged screw holes and same shaft diameter than the common used Mabuchi's), it would be also interesting to know.

I have found this URL in this case:
?PHILIPS???????????CDM9????_jjjjjj1_????
interesting, but all motors not suited for 1:1 exchange

Additional various turntables (motor-pulleys) with set screw for exactly hight adjust are very helpful for motor service by cd mechanism. Therefore brand names for this I want to know. Because there are various clamper forms in use (arround 10 different versions I know) is always necessary to choice the each matched turntable.

Thank you for all advices.

Last edited by tiefbassuebertr; 7th February 2010 at 10:48 AM.
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Old 26th April 2010, 09:35 AM   #2
Salar is offline Salar  Germany
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What is the exact distance between lens and disc surface of CD-players?
Is it based on the focal length each manufacturer can choose in a limited rance, so distances differ between manufacturers,
or is the focal lenght given by a standard ?
All the best,
salar
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Old 26th April 2010, 10:31 AM   #3
Mooly is offline Mooly  United Kingdom
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No known standard as far as I know... as each optical block has it's own characteristics and optics.
I don't even think there is a standard for turntable height either, although it is adjustable on some models (the original Sony D50 mk1 Discman for one).
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Old 26th April 2010, 11:10 AM   #4
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I have note, that the finding of the right distance between lens and surface of compact disc is possible about follow steps:
1) try to find a compact disc without warp, that uses the maximum playing time
2) put in the cd and select the last title
3) about the search funktion forward to about 30 seconds before the end
- Now you will see one half of the lens - if there are one or more warp, lens goes up and down while playing (focus servo error correction). Then choice an other device. Or the lens goes from front to back (tracking error correction) - rare but not impossible, if there are tolerances in the diameter of the hole or motor pulley (CD-turntable).
If the lens reasonably stable reserves its position, pull the mains plug and take a close look changing the lens position.
If the lens in its position does not change (i. e. it does not fall down and not come up more than quarter millimeter), the height adjustment is correct.
This residual tolerance is compensated by the focus servo error correction.
Higher tolerances are even processed yet but lead to thermal overloading of the focus power amplifier (look at that one from NAD502 main PCB and you will note, that height adjustment from loader factory was not correct (at least by the devices, that I have had for service).

BTW - the plastic disc surface is not governed, but those surface where the pits are present and to be read out.

Last edited by tiefbassuebertr; 26th April 2010 at 11:17 AM.
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Old 2nd August 2010, 06:02 AM   #5
anatech is offline anatech  Canada
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Hi tiefbassuebertr,
No.
I am afraid that you are passing along incorrect information here, or information that may only be valid for specific mechanisms. You really have to stop doing this as you are confusing other members who only know as much as you do, or less.

There are many different distance to CD surface requirements as Mooly has correctly stated. In fact, just thinking logically about this should give you this answer. So let's look at a few situations and clear things up a little bit.

Plastic tables that are glued onto the spindle (disc) motor shaft. I don't like these either, but they are in fact serviceable. The adhesive is normally lock-bond (for nuts and screws). These are installed with a jig to set the precise distance. The only problem with this is that we normally don't have those jigs or get the information we need to replicate the setting. Some of these are designed to come out with the motor. These will have a pair of holes that line up with the fixing screws that hold the motor to the chassis. Guess why? In these cases, remove the entire assembly so you can test the motor properly before messing around with the disc table (please!). If you can prove the motor has a fault, heat the motor shaft up a bit with your soldering iron. At some point, the adhesive will soften and the plastic table will release and slide off the shaft. Be careful not to melt or twist the plastic disc table. It helps to measure the exact distance between the bottom (or top) of the disc table to the front mounting surface of the motor before any attempt is made to remove the table. Write this figure down in the service manual you got for the CD player. No manual? Don't touch the CD player! Honestly, even seasoned pros make sure they have the service information for that CD player - or manuals for other machines using the same laser head and motors, and also for the servo section.

The rules for properly adjusting a CD mechanism is pretty common sense. Confirm the mechanism is properly aligned mechanically first. If this is out, the rest of the correct adjustment will not be possible. Don't kid yourself, optical alignment is critical. Once this has been confirmed to be correct, the electrical alignments can be done. Normally there are a number of DC bias voltages that are first up. These can be close to zero volts DC, or may have a bias of 100 mV or so. Read the darn manual a few times before you start so that you understand what you need to do. Read the procedure as you do each adjustment. Note that many multi-meters will peak detect any AC voltage as well. Normally they detect the DC and the positive peaks of any noise. Know you meter (Don't guess), if you aren't sure, assume the worst case for that adjustment. This is where a decent oscilloscope comes in handy as a sanity test. Also near the beginning of the alignment will be the VCO frequency setting. There are a few common frequencies, and most adjustments are done with the control voltage shorted out or turned off. If you are unsure, don't mess with this. The frequency counter you use will be indicating in the 4.3 MHz range, use a X10 probe for all 'scope and frequency measurements. It's helpful to run the frequency counter off the Y1 output of your 'scope. A frequency counter that updates rapidly will make your life much easier here. I would recommend HP/Agilent counters especially, these do update the display more quickly than most others will.

The next adjustments are less critical, the focus and tracking gain settings. Some older machines also have a "kick gain". Don't touch these - ever. There is one adjustment that is very critical, and that is the "E-F Balance". It's very touchy, and if you get it out, the CD player will not play. In fact, it may run the head assembly completely to one end or the other. Breaking nylon gears will probably be the next sound you will hear. I kid you not! Broken nylon parts can not be repaired by any method I know of, time for a donor machine.

If you mess things up, take the machine in for service and tell the technician exactly what you did and in what order. This should be easy from the notes you took while working on it - you did take notes, didn't you?? I still do. Don't lie to the tech, because they will eventually figure it out. This will cost you more money and may invalidate their normal procedures. For instance, I normally don't charge for estimates. If I get someone in who lies about what they did and it causes me trouble, they will be charged for an estimate. Don't lie, it's a stupid thing to do.

As for physical alignment errors from the factory, those will be extremely rare. however, some disc tables can become loose and drift down the disc motor shaft. Same for set-screw type tables. Keep in mind that whoever the OEM was, they make thousands of transports. They are going to use a jig that any mindless fool can successfully use all day long. There are as few measurements made as possible in factories, because each measurement is an opportunity for error and a huge waste of time.

Quote:
BTW - the plastic disc surface is not governed, but those surface where the pits are present and to be read out.
You lost me here. Each and every surface of a CD is dimension controlled. The center clamping area has a specific distance to the surface of the reading side of the CD. The mass is also controlled, because the servo tuning depends on how much spinning mass it has to control. Those stabilizing rings and any other coating are messing up the servo gain and filtering. Don't use them! Same goes for any top surface coatings.

Quote:
Higher tolerances are even processed yet but lead to thermal overloading of the focus power amplifier (look at that one from NAD502 main PCB and you will note, that height adjustment from loader factory was not correct (at least by the devices, that I have had for service).
Well, maybe if that NAD model had a service bulletin that admitted to this problem, otherwise I'm suspicious of your conclusion. It is possible, but certainly uncommon. Having said that, it is true that many CD players had poor servo output designs. Many required larger output transistors with heat sinks attached. The one biggest source of servo outputs overheating is excessive gain settings. That is typically technician induced trouble. The positive (or up polarity) output on the focus servo works harder than the one pulling the lens down because it has to fight gravity. Incorrect table height will also cause this. Normally this is another technician induced fault.

Last tip. I buy the spindle (disc) motors with long shafts. These can be easily cut using a Dremel and cut-off wheel while applying power to spin the shaft. A bit of patience and there you go, the correct shaft length. Break the corners though!

-Chris
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Old 2nd August 2010, 09:19 AM   #6
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Yeah if you dont know what ylu are doing , take it to a tech, we will know if the mech has been messed with and it makes repair that much more difficult,
one quick way to tell if your spindle motor of bad is to hold the assemble on it's side and manualy spin the spindle motor, normaly it should be smooth and you will not feel any vibration, if you do the spidle motor may be shot, it is also too easy to bend the shaft of the motor if you pry of the disc table. Also some disc tables have holes in the to get to the screws that hold the motor to the chassis. If you suspect the laser (most common fail i see) you need a scope to look at the rf test point you need to set the scope to see an eye pattren, if it is fuzzy or has low amplitude that may be the fault. Grease has been known to migrate into the optical block(laser assy) on older sony models and cause problems, sony has since changed the type of grease. I have been able to dissasemble some blocks and clean them but you need to be very careful as first surface mirrors are easy to damage, dust gets in there as well and effects things.
Sadly with newer machines focus bias and tracking gain are automatic and may not compensate for an aging laser, also another tip is to never mess with the pots on the optic block it's self, it may get an older laser working agen but will greatly shorten the life of any block as it over drives the laser diode past the automatic power control the system has.
please don't take what i say as fact it's just my working experice i have seen while employed as a repair tech and as others have pointed out, get the service manual if at all possible. I too don't charge a bench fee, but the shop i work for does, it seems more common that service shops do this so people don't just give us junk they find at the side of the road lol.
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