CD drive spindle servo logic

I've been given a radio/cassette/cd player with a faulty CD portion to play with.

The CD spindle does not spin, but the motor operates if given 4+ volts from a battery (and draws a variable current depending on mechanical load).

The laser actuators appear to work, because they attempt to hunt for a CD to read. What I am not clear about is whether the focus process can work with a stationary CD.

I consulted

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*.html which suggests that if the spindle does not start this may because of failure to focus, implying the answer to my question is "yes"; but how?

Reading the specification for the "RF Amp + SSP" chip (KA9220C) does not help me much either. However it does say "The KA9220C is designed for 3- spot type optical pick-up assembly. ... The photo detector A,B, C and D detect audio modulation signal on the disc and generate focus error signal." That suggests to me that the disc needs to be rotating for focus to happen. But if the above answer were "no" we would have a Catch-22 situation!

Can anyone explain, please?

Mike.

Reply to
Mike
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** All the CD mechanisms I can recall seek focus before spinning the disk.

The most common failure seen in budget CD mechanisms is a weak or dead laser diode - which would produce the scenario you describe.

... Phil

Reply to
Phil Allison

Or dirty.

Reply to
jurb6006

Also, there is the possibility of a bad motor driver. This is not always an IC. It oculd be just a ocuple of transistors. If the spindle motor starts pulling too much current it can blow the driver. If in doubt, follow it bac k to whatever drives the motor to see if it is getitng dsrive but not drivi ng. In that case the spindle motor might be bad.

The circuit is usually simple as hell. It is off when the buffer is almost full and on when the buffer is almost empty. And a transistor maybe for bra king, if it even has that it usually just shorts out the motor so to load i t and stop the disc. They don't use a negative voltage usually they just ca lculate the mass of the disk and with the motor loaded by the short it must stop ithin a certain time.

You say it is a combo unit ? Expect the absolute cheapest of circuitry. In fact if it has a pop up door instead of a drawer it probably has no braking and just has one transistor to drive the motor, on or off. Might even be a DTC something because the current is low.

Or supposed to be.

If you can get a print and find the FOK line and check it that is fine, but if whatever drives that motor is not told to turn on you can pretty much a ssume you don't have it.

I would clean the laser. what's more if you clean the laser and it starts w orking, tap on it with a screwdriver handle or something and see if it skip s easily. then you got a weak laser. It will work for a time, BUT it is reg ulated so it will not last.

If you decide to tweak up the laser power ith that little pot, remember it is not going to last long and probably will still skip easily until it fail s.

It is nice practice probaably fixing those thihgs but you are not goiung to make a fortune at it. Also, in some cases you can get the whole CD drive f or about the cost of the laser. (I had a bad new one once and had to franke nstein the damn thing between parts from the new and old because the job ha d to go out, piece of shit)

Reply to
jurb6006

Thanks very much to all three of you for your comprehensive answers.

The unit is an Alba CX500L which is a budget brand and I haven't been able to find any schematics or service manual. So I have left the four tweaking pots on the PCB strictly alone! They are marked only with schematic IDs. However the PCB does have numerous test points marked so I may play a bit more... Also the actuator and spindle motor drivers are combined in IC KA9259D and I have a specification sheet for that.

This is merely a learning hobby exercise. As soon as it gets too boring the unit will get junked; I am unlikely to spend any money on it!

Mike.

Reply to
Mike

I've been out of the consumer electronics service business for 15 years so this comment may be off base. Back then cheap cd spindle motors would begin turning at 3 volts not 4. Have you blasted the brushes with contact cleaner, spun the motor at a higher voltage for a few minutes, and cleaned and lubricated the bearings? When Pioneer cd player motors went bad, spinning the disc by hand would start them playing. If this works, you'll know the motor is bad. Chuck

Reply to
chuck

Yes I'm in the U.S. I used to work at Best Buy's corporate headquarters. I was pretty sure that the motors turned at less than 3 volts but I couldn't remember the exact voltage. It was likely that, if it didn't turn until 4 volts, the motor was defective. Chuck

Reply to
chuck

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