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Old 28th March 2012, 07:10 PM   #11
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Thanks Mooly.

I just got the service manual, and found the places where the signals are coming from the microprosessor to the motor driver.

Since I do not have a scope, I will check with my multimeter, just to see if the signal ends after a second or so, or that that the processor is continuing driving the motor.

If I do not get further, I will get a scope. Or a cheap Philips CD723 player. The 723 and the CD4000 share the same mechanics (and electronics).

Haik
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Old 29th March 2012, 07:07 AM   #12
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A scope is the best tool for faultfinding.

When the servo loses lock on the CDR's then it's a bit like a computer crashing or locking up. There's no fault as such but nothing works or responds until the processor is reset.

There won't (99.999% sure) be a processor or motor drive fault. It's down to the way it's "seeing" the data on the CDR's.
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Old 29th March 2012, 11:52 AM   #13
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Interesting. What is then the next step? Is it the laser unit? If I replace it, will the problem be solved?
The VAM1201 is available on the internet for around € 20.

Haik
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Old 29th March 2012, 03:57 PM   #14
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I'm surprised that a CD player is able to spin backwards. The facility to reverse polarity to the motor must be there for a purpose, presumably for braking?

I'm not an expert, but one purely logical explanation for both problems is that the servo has lost its sense of the motor going too slow. Fast backwards is just an extreme case of too slow. Are CDRs more densely packed, requiring the disc to slow from some nominal speed more than usual? Maybe it then slows too much at the first guess and can't recover. Similarly with the brake, where the "too slow" signal should result in switching off the motor. Long shot...just encouraging positive thought.

If the fault changed as a result of you cleaning contacts, it could be that just handling the board restored a poor connection until either it got warm or was disturbed by the operation of the drawer or laser sled. By the same token the fault is unlikely to be component failure.

Is there somewhere an analogue voltage that represents motor speed error? You could examine that with a voltmeter, and check that errors of both polarities are reaching their intended destination. Look for dry joints or cracked tracks (use a magnifying glass) in that area. Similarly for parts of the servo circuit that get hot or stressed by the mechanics of operation, or handling. Check for hairline cracks in ribbon connectors too.

I've got a Marantz CD50 that's sticks in fast forward every time I replace the front panel. It's driving me mad.

Ian
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Old 29th March 2012, 06:03 PM   #15
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Quote:
Originally Posted by haik View Post
Interesting. What is then the next step? Is it the laser unit? If I replace it, will the problem be solved?
The VAM1201 is available on the internet for around 20.
Haik
The next step is this

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The answer to this is to look with a scope at the signal. Unless you do detailed tests and gather and understand all the information then you are just guessing as to the cause.
There is no guarantee that a new pickup will fix this. It may or may not. Without actually confirming the quality of the signal from the laser it's all guesswork.
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Old 29th March 2012, 06:19 PM   #16
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Are CDRs more densely packed, requiring the disc to slow from some nominal speed more than usual?
CDR's are fundamentally different in the way they "reflect" the laser light.

A transistion (which is interpreted as a change from logic 1 to a logic 0) in a normal CD occurs every time there is a change from a "pit" to a "land" on the reflective layer. The pits and lands are equally reflective but due to the wavelength and the monochromatic nature of the laser light, if the lens is "focused" on say the lands, then the light reflected from the pits is not seen by the photodetector sensor as it is seeing the "null" point in the reflected light here. Bit hard to explain easily

A CDR uses a dye that is "burned" to make the pits and lands. There is no reflective property where the dye blocks the light from being reflected. The sensor still sees a transition though.

The problem is that CD's are pressed and have accurately defined pits and lands with clean edges. CDR's are not as precise and the point where the burned dye starts and finishes is not as clean and abrubt change as in the pressed CD's. This show up clearly on the recovered signal when viewed on a scope.

The problem with the front sounds like it's pressing on one of the tact swithes.
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Old 29th March 2012, 08:04 PM   #17
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I have read the service manual. There is a service menu so you can run the CD player is a test mode.
I tested everything. Spinning CW and CCW. Moving laser to the edge of disk and back. Everything works. The CD accelerates well, and stops also fine. So the signals coming from the processor are good.

What fails is the "FOCUS". It gives an error. There is a way to change the focus by defining CD-R or CD-A disk. Both fail in the test (but in real life, only CD-A originals are working).
I also tested the focus of the laser, and it fails (the going up and down of the laser lens). The lens goes up and down, that works, but does not find the focus. Cleaning the lens did not help.

So I still think the processor gets wrong information, and does not find or know about the CD. That is why it does not stop the reverse spinning.

So Mooly, you might be right. I think I will order the laser unit (especially now in the manual it is shown how to disassemble the mechanical unit).


Haik
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Old 29th March 2012, 09:54 PM   #18
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Quote:
Originally Posted by Mooly View Post
CDR's are fundamentally different in the way they "reflect" the laser light...
Thanks.

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The problem with the front sounds like it's pressing on one of the tact swithes.
Sorry, I mean the motor runs forward, fast. Not like pressing the fast forward key. The buttons all click and work as far as expected with no CD loaded and the motor permanently running. It's not an earthing thing either, and the boards are all seated properly and appear relaxed.

Having solved the problems it had when I got it, I'm now upset and it's in disgrace. I'll look at it again when I feel calmer. Thanks all the same.

Ian
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Old 29th March 2012, 11:06 PM   #19
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I think we agree that the processor is not getting the right information. The problem is why not.

I'm surprised that the machine relies entirely on feedback from the laser to determine its spin speed. I'd assumed two nested loops, with the inner one derived from the motor itself. Oh well...logic isn't always the best guide.

I'm new to CD players, which is why I'm here, so I'm learning, thanks.

So, if a player of this kind loses focus whilst playing a CD, it's normal for it to go into a fast reverse spin if "stop" is pressed?

Ian
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Old 30th March 2012, 06:27 AM   #20
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Quote:
Originally Posted by haik View Post
I think I will order the laser unit (especially now in the manual it is shown how to disassemble the mechanical unit).
Haik
Without a scope that is probably all you can realistically do... lets hope it's a fix.
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