The Workbench

Re: Workshop Beogram CD / BeoCenter CD - How to adjust the CD Laser Current

Die_Bogener — Fri, 15 May 2009 07:49:43 GMT

Yes, it is possible to transplant the laser pickup from a newer drive in a older one and the other way. The pickup's are compatible.

Also the foil cable is compatible, the length and signals are identical.

Re: Workshop Beogram CD / BeoCenter CD - How to adjust the CD Laser Current

yachadm — Fri, 15 May 2009 00:40:53 GMT

Hi Martin,

So what you are saying is that you can take a laser pickup unit from a CDM4/19 or CDM4/25 and put it in a CDM2/10 transport?

Is there no problem with different lengths of the foil cables?

Are all the foil cable lengths, the same?

Re: Workshop Beogram CD / BeoCenter CD - How to adjust the CD Laser Current

Die_Bogener — Thu, 14 May 2009 13:52:01 GMT

Yes, i have done some of these replacements. The laser pickup can be removed and installed on the other drive. It's compatible to the old and the newer version. There are just 2 bolts for the assembly... pretty easy. Just take care for the the foil cables, that's all.

The motor itself cannot be disassembled without special tools, but this is usually not necessary.

Re: Workshop Beogram CD / BeoCenter CD - How to adjust the CD Laser Current

yachadm — Thu, 14 May 2009 07:07:20 GMT

Thanks Martin & Martin - good points.

I'm considering changing the CDM2/10 (also labelled CDM-2 03011 - see picture) to a CDM4.

Have any of you ever done this / had experience / know which version of the CDM4 would be suitable? I do have a source for a new CDM4 at a reasonable price, but I would still like to be sure that an upgrade is possible, and with which version.

Menahem

Re: Workshop Beogram CD / BeoCenter CD - How to adjust the CD Laser Current

Dillen — Thu, 14 May 2009 06:22:55 GMT

Also worth noting that some servicemanuals gives a wrong place for measuring the laser current (sometimes also referred to as focus current, which is confusing).

Martin

Re: Workshop Beogram CD / BeoCenter CD - How to adjust the CD Laser Current

Die_Bogener — Thu, 14 May 2009 05:43:27 GMT

Hi Menahem,

the CDM 2 is a little bit different to the CDM 4 drive, the motor and the laser pickup changed. The older CDM 2 drive is specified with a laser current adjustment of 40 mV, the newer CDM 4 with 50mV in the manuals (CD5500 - 7000).

But: the 50mV of the newer drives seems not to be correct, if you check it in a original and never modified CD7000, then there is a adjustment of ~ 40- 42 mV. And the drive works better with this adjustment.

I would recommend to keep the 40-42mV adjustment, even with the newer drives.

Martin

Re: Workshop Beogram CD / BeoCenter CD - How to adjust the CD Laser Current

yachadm — Wed, 13 May 2009 09:56:17 GMT

Now, I could return the CD mechanism back to its normal position in the cabinet.

Thanks to good engineering, a small hole is conveniently located in the cabinet base directly in-line with the pot, enabling access from the underside of the cabinet (I believe that the BeoGram CD has a similar access hole).

The 2 wires are now draped over the CD player, and connected to my DMM, set to"mV".

Position the CD player on a shelf, with the CD part slightly overhanging, to provide underside access to the pot.

Insert a 2mm hex key from the underside of the cabinet into the pot, insert a disc, and press PLAY.

You'll see the mV readings on the DMM, slightly fluctuating, and adjustments can be made to read an average 50mV.

Having done this, my CD's are now playing correctly.

Workshop Beogram CD / BeoCenter CD - How to adjust the CD Laser Current

yachadm — Wed, 13 May 2009 09:47:24 GMT

I have now finished the repair of my Philips CD650.

The most complicated part of the repair was getting the CD to play all my discs, without skipping, or any other problems.

This CD player (made by Philips in Belgium) has the Philips CDM2 CD laser mechanism and transport.

This is exactly the same mechanism as is found in the BeoGram CD5xxx range, as well as the BeoCenter 8000 and 9000 series (Some B&O models have the CDM4, which is basically the same unit, with minor differences).

Even the Printed Circuit Board is identical (minor revisions may be apparent on different models).

On the CDM2 PCB, I replaced all the electrolytic caps, including the infamous C2103 (new 47uF).

So, the last part of the repair was adjusting the laser current.

I have read horror stories about burning out the laser, so I was a little nervous about doing this, but I had no choice other than to jump in and do it, because none of my CDs were playing correctly.

I have the original Philips CDM2 Service Manual, but in Dutch, so I had to refresh my translation skills, and "focused" in on the area which deals with laser adjustment.

Simply, to set the laser current correctly, potentiometer R3106 - the 1KOhm pot in the centre must be adjusted in order to give 50mV +/- 5mV across R3102.

So, knowing that it is impossible to adjust and measure at the same time, I soldered 2 longish wires onto either side of R3102.