The Workbench

Re: Test CD / Laser Focus?

auric — Fri, 07 Nov 2008 15:54:40 GMT

Marc, Martin:

Thanks for your assistance with this. The problem turned out to be the spindle table height.

The spindle motor was replaced with new a new one and the table was too high.

Derek

Re: Test CD / Laser Focus?

TheTinman — Tue, 28 Oct 2008 11:22:22 GMT

You would ideally need an oscilloscope. Adjust the focus offset on a burned disc for clearest eye pattern. Then go back and adjust laser current to spec. You did (stupid question) clean the lens with 99% alcohol?

Not quite by the book, but I find that I can get finer alignments by using the scope to see what the laser sees.

Of course, the laser may actually be getting tired, in which case increasing the current will help, but only a short time. It will actually die even faster if that's the case.

I know these mechs can all read CD-R's. Even my CD-100 reads CD-R's, but I did have to fine adjust it to get optimal results. There were a few it would hickup on. I have one CD-100 that turned out to have dirt in the optical assembly. I took it apart and ultrasound cleaned it.

Let me tell you, it took forever to get it aligned again, but I did save it. This is a pre-production sample without ANY part numbers. I was highly motivated to make it run.

Re: Test CD / Laser Focus?

auric — Tue, 28 Oct 2008 10:51:22 GMT

Thanks Martin.

So just use a commercially pressed CD and adjust for 400mV per the service manual?

Derek

Re: Test CD / Laser Focus?

auric — Tue, 28 Oct 2008 10:49:41 GMT

Marc:

My 9500 (similar Phillips cd mech) as well as all of my other players plays these CDRs just fine so its not likely the media.

How do you fine tune the focus offset on the philips radial mech?

Derek

Re: Test CD / Laser Focus?

TheTinman — Mon, 27 Oct 2008 18:07:31 GMT

Even today, playing back CDR's can be a hit and miss proposition on any CD player. It depends on the media type and how FAST it was burned. You should see the poor eye pattern I have seen on the scope when playing lousy media.

What always works for me with all my philips based players is to use good media and burn at 4X or slower.

You might want to fine tune the focus offset before you mess with the laser power, btw.

Marc

Re: Test CD / Laser Focus?

Dillen — Mon, 27 Oct 2008 02:16:26 GMT

There's nothing like a good test CD. If you have the original B&O set with two CD's, the one with "intended defects" is particularly good for testing the result of the service (obviously, this is what it was made for).

Having said that, it's correct that replacing the caps on the decoder board will improve things slightly. Focus (and radial balance) do have some mechanical limits though but all B&O decks will normally play CDR's without problems. The focus is the problem with CDR's, because where the info layer in a normal factory CD lies in the center, sandwiched between two layers of polyester or similar, the CDR has the info layer sprayed onto one side of a thick polyester carrier, so the focus point is further away from the laser lens on a CDR. A CD player will normally be able to compensate for CD's that are not perfectly flat (wobbling slightly up and down as they rotate) but take a cheap CDR and maybe even a particularly wobbly one, and you will have a focus problem.

Failing to read and/or track some CD's could also be as simple as too low laser current, that's an electronic adjustment that can be made with a normal audio CD and even, in the case of f.e. the Beogram CD50, without a CD.

Check capacitors in the power supply as well.

Martin

Test CD / Laser Focus?

auric — Sun, 26 Oct 2008 12:41:11 GMT

Dillen:

Is there any way to adjust laser current on the CD players with the Philips radial mechs without using the Test CDs?

I replaced the 47 uF cap on a BC2500. It plays pressed CDs fine but has trouble with CDRs. Sometimes the audio distorts slightly, other times it plays fine and then just stop mid way.

Dig Bogner suggested in an earlier post better filter cap and focus current will allow better compatibility of discs.

Suggestions?

Thanks,

Derek