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Old 04-04-2010, 07:32 AM   #1
PowerAmpFreak
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Default Micromega CD player repair

I was doing a ordinary change of a laser unit and mechanism on a Micromega stage CD-player. The laser unit is a Philips CDM12.4.
After laser change, player refuse to play one single cd. Here is what happens:
Tray closes. Laser succeeds focusing. Cd starts to spin, though way too fast,
3 seconds later display shows "ERR".
If closing tray without having a cd in, the display show "No disc" which means the laser can focus correctly and actually works, right?
The CDM12.4 laser has an onboard RF amp, as can be seen in the picture.
Before the laserchange the player actually worked, but had reading problems.
Any advice is appreciated.

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Old 04-04-2010, 08:12 AM   #2
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Default Re: Micromega CD player repair

disk spinning out of control is an unreadable signal.
you can get this if the bias or gain on the laser is wrong.

another symptom is the disk moving in small bursts & the laser lens clicking.
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Old 04-04-2010, 08:31 AM   #3
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Default Re: Micromega CD player repair

Thanks for fast reply, stj!
There are no adjustments for gain or bias, only laser power which is set as the old pickup.
The cd spins up maximum speed for 3-4 seconds, drops to near zero, and repeats again.
I wonder what I can do to make it work..
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Old 04-04-2010, 12:47 PM   #4
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Default Re: Micromega CD player repair

scope the eye & look at the pot on the laser assembly.
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Old 04-04-2010, 12:48 PM   #5
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Default Re: Micromega CD player repair

and look at the caps in the psu, there may be ripple causing the laser to not read clearly.
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Old 04-05-2010, 03:20 AM   #6
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Default Re: Micromega CD player repair

Quote:
Originally Posted by stj
scope the eye & look at the pot on the laser assembly.
You mean scoping the RF amp data output, and watch for the "eye" pattern?
What do you mean by "looking at the pot"?
Didn't check for PSU ripple, but all +5VDC was nice and stable.
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Old 04-05-2010, 08:03 PM   #7
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Default Re: Micromega CD player repair

Does the laser emit?

Most laser assemblies have a switch or a piece of flexible wiring which can be safely cut off (read the service manual first), to protect the laser diode from static.
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Old 04-06-2010, 10:57 AM   #8
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Default Re: Micromega CD player repair

Quote:
Originally Posted by japlytic
Does the laser emit?

Most laser assemblies have a switch or a piece of flexible wiring which can be safely cut off (read the service manual first), to protect the laser diode from static.
Guess it's not possible to focus correctly if laser doesn't emit, right?
The player can determine if there are a CD or not inside, which I assume is a result of focus ok...
With no cd display show "No disc", with a disc inside it show "ERR".
Other lasers I've replaced all did contain a solder jumper which must be desoldered (for ESD protection), but I can't see any on this dude.
May be probably due to the RF amp fitted on the laser assembly itself, minimizing ESD problems, since laserdiode is "already connected" and properly terminated to the RF frontend.
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Old 04-06-2010, 10:42 PM   #9
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Default Re: Micromega CD player repair

no, it may focus well enough to detect a disc, but not well enough to actually read it.
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Old 04-07-2010, 05:22 AM   #10
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Default Re: Micromega CD player repair

Quote:
Originally Posted by ratdude747
no, it may focus well enough to detect a disc, but not well enough to actually read it.
Yes, so the answer to the question "does the laser emit" must be YES since it's actually able to focus at all, though doesn't read it correctly, right?
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Old 04-09-2010, 02:04 PM   #11
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Default Re: Micromega CD player repair

The laser gives a decent 1V peak-peak RF signal measured right at the RF amp output. The "eye pattern" is visible but not that clear. If memory serves me right the eye pattern should be pretty sharp and clear. So could this mean the new laser is actually bad?
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Old 04-12-2010, 10:28 PM   #12
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Default Re: Micromega CD player repair

Believe it or not, but it appears my "new" laser was an old used one which the company where I ordered it, cannot explain. A new laser unit is on delivery!
Hope for better luck next time.
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Old 04-17-2010, 10:20 AM   #13
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Default Re: Micromega CD player repair

The new laser arrived, this time it was new and not used...
Unfortunately it didn't make any difference to the repair. It still shows "ERROR" in the display. There are just above 1V peak RF amplitude, and the "eye pattern" is visible. Have no idea why the player refuse...
There are no adjustments except for laser power which appears to be good since the RF level is ok. There are a few screws on the laser unit covered with glue so you shouldn't touch these.
Anyone having a hint?
Regards,
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Old 04-17-2010, 04:10 PM   #14
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Default Re: Micromega CD player repair

Checked the draw is closing and activating any relevant switches correctly.
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Old 04-18-2010, 01:11 AM   #15
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Default Re: Micromega CD player repair

yes, that seems fine, as soon as the tray enters "home" position, the laser unit begin to focus, cd starts to spin, but it speeds up too much, probably because it isn't able to read the disc properly (for any reason)...
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Old 03-14-2014, 02:18 AM   #16
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Default Re: Micromega CD player repair

Hi All,

I have the same issue for this case on my micromega player too. have anyone resolve this issue ? Thanks
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