Philips CDM-2/10 Laser Tuning - diyAudio
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Old 8th July 2012, 07:24 PM   #1
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Default Philips CDM-2/10 Laser Tuning

I am looking for step-by-step instructions, with photos, to show how to set the CDM-2/10 laser diode voltage to 50mV for correct focusing of the TOC on a CD. I have the Philips C.D.M.-2 service manual, but it is not specific on which resistor on the control board (CB) must be used. I have seen comments here that it is located in the bottom right corner of the CB. I believe this to be R3131.

I remember searching the web and finding a site where this information was contained, but have since lost that history on my browser. I have read Laserology by, and while very informative, it is not specific enough for me. Yes, it shows the pots and what they are used for, but not the resistor location on the underside of the CB.

I have also read CDM2 Revision by Bakura, and while informative, not what I am looking for. The closest I have found is the CDM 4/19 to CDM2/10 laser swap blog on - and while getting close to what I need, it is still short of what I once saw on the web.

Any pointers or URLs are most welcome.
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Old 9th July 2012, 05:37 AM   #2
absolon is offline absolon  Canada
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Find it here in the Condor Audio Magnavox CD650 restoration guide, top of page 6
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Old 9th July 2012, 06:05 PM   #3
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Yes, this will work. It is not the one I saw previously since it had two wires connected to R3102 and hooked up to a volt meter showing 53mV. Nevertheless, this provides the necessary resistor number and location for the tuning.

Thanks a bunch.

Off to the lab...
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Old 9th July 2012, 09:34 PM   #4
absolon is offline absolon  Canada
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Actually, this does specify that you solder a jumper wire long enough that you are able to flip the transport right side up to either side of that resistor and measure the voltage on them, yellow lines at the resistor in the picture on page 5 indicate the locations to install the jumpers.
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Old 10th July 2012, 05:01 AM   #5
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For Philips models with the floating loader, the mech can be very easily flipped up on its nose and secured in a slot moulded into the base for the purpose. Nothing else needs to be removed or disconnected. It can be run and adjusted in that position, in which case it is wise to remove the drive belt in case you accidentally hit "eject".

I have never found the laser test voltage to be out of range, luckily. Old presets can be difficult to adjust without becoming unreliable.

It's worth checking the voltages supplied to the mech. The CD650 supplies unregulated DC at voltages way out of spec for the servo board, and a transistor gets very hot as a result. Rather than adding regulators to the servo board, I inserted pre-regulators ahead of the main +5V -6V supplies. This method has the advantage of dissipating heat to the main heatsink rather than under the mech. Seems to work well.
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Old 13th April 2014, 02:42 PM   #6
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I have tried to adjust my CD555 compo system, but it seems I can't get more than 32mV to the laser even if the potentiometer is turned all the way. I just went through the service positions and the mech could only get the focal point when the voltage was maxed. And that didn't work every time either. In the service position 2 it seems the rpm is maxed. In the manual of CD-371 it says that "If the HF signal is not well coded or no disc is present, the turntable will start rotating at maximum speed".

So, what could cause the low voltage? ATM, the player wont recognize CDs.
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Old 14th April 2014, 02:25 AM   #7
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It's pretty darn certain you have caps going bad. Specifically the European-made electrolytic caps in the servo area. To make any of these old Philips units reliable, the best thing is to simply go through and replace any lytic caps that aren't already Nichicon with Nichicon.
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