Laser surgery on CDM-x - diyAudio
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Old 10th October 2004, 01:53 PM   #1
Thomas is offline Thomas  Denmark
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Lightbulb Laser surgery on CDM-x

For a long time now, I have thourght about why anyone hasn't tried to replace the laserdiode itself on a CDM mechanism. Why? - For obvious reasons. Spare CDM mechanisms are getting harder and harder to find and 99.999% times a mechanism fails are because of the laser had died.

I had a CDM-4 arround which are skipping. I used it for a little 'test'. I don't have any spare laserdiodes arround, so I decided to try remove the old LED and re-inserting it again.

I can't say my first attempt was entierly sucessfull, but I managed to get the job done!

First step was to desolder the LED from the flexband. The flexband won't cripple or burn because of the heat. I used my soldering station set at 250 deg C. The first picture is showing that. I managed to break one of the soldering pads off the flexband. A small piece of wire was later used to 'fix' that.

Pictures at: http://cdmsurgery.diyaudio.dk/

The next step was to remove the LED. I turned the soldering station to 400 deg C. I used the heat and and a thin scalpel to remove it. The LED is held by two blobs of glue only.

Lastly, I re-inserted the LED and soldered the flexband in place. If I didn't break the solder pad it would have been easier.

This is my first (and probably anyone's) attempt to hack a CDM transport. I re-installed the drive in a crappy Philips cd164. When powered and no CD inserted, the motor spins, the arm moves and I can see a red light from the lens. The display then reads 'no disc'. - So far, so good. With a CD in the drive, it searches around for a while and then, the display reads 'E'.

So, the drive can 'see' if there is a disc inserted or not, but it can't actualy reed it. Probably because of missalignment somewhere?? I will peek and poke arround and see what happens. Maby I can get it to work.

I have ordered a replacement laser LED, but I don't have anymore bad CDM mechanisms to try on. Because of the flexband accident I'd rather try with a 'new' burnt out unit next time. If someone could mail me a bad CDM-4.19 it would help further experiments. I hope some day to be able to repair CDM-0/1 mechanisms this way. I would need a whole player with a burnt out laser for that.
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Old 12th October 2004, 07:12 AM   #2
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Read the thead

Sony CD head repairs !!!

might be useful

Gajanan Phadte
_-------________--_-_-_-_-_---__------____-
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Old 12th October 2004, 10:48 AM   #3
Thomas is offline Thomas  Denmark
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The cheap philips player I talked about don't seem to be able to read error codes, so I'm using my CD72 now instead. Still, there is a difference between no cd and cd inserted. No cd reads 00 and when in service mode I get code 7 - no TOC I belive. I got the codes from a CD80 manual, but I'm asuming they are identical?

I have located a source for laser diodes. they are of the exact same specs as the original ones. I still need to figure out how to allign them properly though. Any Ideas?
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Old 12th October 2004, 10:54 AM   #4
Thomas is offline Thomas  Denmark
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Quote:
Originally posted by gmphadte
Read the thead

Sony CD head repairs !!!

might be useful

Gajanan Phadte
_-------________--_-_-_-_-_---__------____-

I'm sorry, but no. I'm talking about Philips products only. I have read just about everything about the CDM's I could find and noone seem to have done this before.
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Old 12th October 2004, 12:42 PM   #5
brianuk is offline brianuk  United Kingdom
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I dont understand Thomas, it looks like it just fits in with the location slot at the side.

Maybe I cant work out from your pictures?
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Old 12th October 2004, 01:21 PM   #6
Thomas is offline Thomas  Denmark
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Quote:
Originally posted by brianuk
I dont understand Thomas, it looks like it just fits in with the location slot at the side.

Maybe I cant work out from your pictures?

You are right. It should fit just back in.

Laser diodes are very sensitive to ESR. Maby it's damaged somehow, but appears to be working. Maby the heat from my soldering iron did something to the diode??? I will find out later this week, when I get my replacement diodes.
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Old 12th October 2004, 01:29 PM   #7
brianuk is offline brianuk  United Kingdom
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Goodluck Thomas, hope it works out, there a lot of precious players out there that need your help!

Apart from that - fixing them is great for the environment too.

Wonder how many CD100 are in land fill
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Old 12th October 2004, 01:47 PM   #8
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From talking to friends who have worked at local repair shops, and having been in electronics repair Myself, for way too many years now , I have found that many of the failures are from the "Flying coil" system too. the Flying coil gets out of spec or alignment, and the diode misses it's mark. You might have one of these failures on the system you are working on.

YMMV!

Tall Shadow
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Old 12th October 2004, 11:05 PM   #9
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Hi Thomas,

Check your PCB and look for a test point labelled RF. Monitor the RF signal on oscilloscope and look for an eye-pattern. It should be 1.5(+ or - 0.3) Vp-p. If it is lower than 1.2V you'll have the problem where the pick-up reads some disks, and does not read ones with low reflectivity. You can increase the laser output by adjusting the little trim-pot located on the pickup itself. Do not go over 1.7 - 1.8 volts.

Regards,
Extreme_Boky
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Old 13th October 2004, 04:51 AM   #10
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I do not know about CDM's, and
it looks like there is no objective lens in there and no coils either

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A skilled carpenter could easily repair a CDM assy if the fault is non galvanic
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