Beocenter 9000 CD problem

Hi

 

First post here, after reviewing many, many threads about the CD4 mechanism and board used in the Beocenter 9000. I have the usual problem of disk rejection, failing to play, etc, with the occasional play on really clean disks. Naturally C2103 is the assumed culprit.

I replaced C2103 with a Vishay 030 BC 47uf 16v capacitor, axial. I think the problem is improved but not much. Is it because the capacitance is wrong or the type (030 series)? I've ordered a Vishay "MAL203851339E3 33 µF, 50 V, 038 RSU Series, ± 20%" from Farnell in the UK, it's an 038 series capacitor. I've read that 47uF is OK if its a Vishay cap, but I'm not sure what the difference is in spec between 030 and 038 series caps - anyone care to enlighten me?

Also, I'd like to measure the laser voltage (50mV) but I can't see where the test points are on my board. It's because there are no markings for any of the resistors and I don't have a schematic or layout despite searching the Interwebz for ages. Yes, I found various pictures and other information about the CD4 as used in the 9000, but they seem to have different PCBs to mine. I also found a Beocenter 9000 service manual in Dutch and French but it hasn't got the CD PCB layout or schematic.

I've attached a picture of the board (click to see it all). Can anyone provide a schematic / board layout for it so I can work out where the test points are, please? Best I could find was the 9500 service book but it has the wrong PCB version.

Finally, I noticed the player seems to work better when it is on its side (in the "maintenance position" as the manual calls it). Not sure what this points to.. maybe the ribbon to the head is marginal? Looks OK..

Thanks

JonB

 

 

From memory (not clever nowadays) you measure between pin 28 on the big IC and the link wire in the bottom right corner of the board. It should not need adjusting if you have only changed c2103.

You are supposed to play a special test cd without faults.

Beware! It is very easy to ruin your laser!!!!

Yeah.. I'm thinking that I don't want to go there if it's not necessary. But I'm disappointed the cap swap hasn't cured it. So many of them seem to have been fixed by virtue of this one component.. not mine though! Unless the cap I put in is wrong?

I assume you mean the points marked on the attached picture.

Sorry for the multiple posts, the forum only allows me to attach one picture to any single post.

 

So, I attached a scope to the measurement points and got the unit to play a CD (seems to like working on its side for some reason). The wave form is attached. 

This doesn't look like the correct place to measure the 50mv for the laser. Although if it was, I'd expect a meter to show ~75mv as the average.

Found the servo PCB in the 9500 service manual on page 2-13. It's called "Board 30" and it matches mine more or less exactly.

 

Now to do some tests....

R3105+R3106 measures .51K Ohm. It's supposed to be 1K according to the manual.

R3102 has 42mV across it (should be 50mV).

...but dare I turn the potentiometer...?

In the spirit of impatience, I set the potentiometer to 1K Ohm and started the player. I measured 21mV across R3102 yet the unit is playing. So I have to assume that the 1K setting (R3105+R3106) is a safe starting point for setting the 50mV across R3012, is that correct?

I have gone through my library of B&O manuals which are not on Beoworld and found a couple which may be helpful.

The CD of these units was changed and if you have the CD4 which I think you do, then that is the newer version.

Attached is the servo layout which may be your version, please check?

jonbr:

In the spirit of impatience, I set the potentiometer to 1K Ohm and started the player. I measured 21mV across R3102 yet the unit is playing. So I have to assume that the 1K setting (R3105+R3106) is a safe starting point for setting the 50mV across R3012, is that correct?

I think you are on the correct track here

 

Thanks Keith, but it looks like this version (note twin potentiometers). Should I up the voltage to 50mV..? Or wait until the 33uF cap I ordered turns up, fit that, then adjust?

 

 

Further testing shows it is behaving oddly. When loading a CD it fails to read track 1, but select 2 and it will play. Then, select 1 again and it plays that! How come it can't play Track 1 when loaded, but a skip forward and back again and it works? Is this indicative of any known problem?

(By the way, I still have the 47uF Vishay cap at C2103 and the laser voltage at 21mV.)

 

Edit: Also I suspect a loose wire somewhere. On reseating the drive in its normal position it rejects the disk. Back in Service position and it is rejecting the disk. Settle it back down in its proper position and it plays. More testing (different CD) and it is rejecting, than after slight movement of the player mechanism, playing.

 

Edit 2: Scratch that - the servo board was shorting against the chassis (d'oh!) causing the disks to be rejected. It is still failing on Track 1 as before).

Don't touch the potentiometers unless you replaced the laser (or already messed with them).
Most read errors are down to bad (or wrong type) capacitors on the servo board, cracked solder joints at the large filter capacitors in the
power supply module and/or craced solder joints at the large transistors on the decoder board (depending on drive version).

And note that some manuals give a wrong point for measuring the laser "current" - a point that will never reach the stated readout, allowing the laser current to be set high enough to burn the laser.

Martin

Too late, Martin, I set the R3105+R3106 measurement to 1K per the manual and got 21mV across R3102 (previously it was 48mV). Unit is playing better now, but is unable to read Track 1 when a disk is first loaded - but after seek to Track 2 then back to Track 1 it plays. I've been searching the forums all day looking for answers. One post suggested it may be caused by dirt in the laser mechanism and that I should clean it, but I could not find any clear instructions on how to do this. I have cleaned the outer face of the laser lens but that is all I could get at. I've not removed the laser housing / cover yet. Any ideas how to proceed?

 

Edit: But.. there is a small bump stop on the laser carriage that looks to have become slightly dislodged. Its white plastic, like a little dimple that looks as if it slides in a groove. I pressed it home and cleaned it a little. Hasn't really helped, but I found if I load a disk then (when it is trying to play track 1) touch CD, it plays. Maybe it is going to pause when loading?

Just a thought.

When you LOAD a CD, is it supposed to start playing automatically, or do you need to touch CD to make it play? I've just reviewed the instructions, and it seems that LOAD on its own won't make it play. It just closes the door and indexes the disk. Which means that the behaviour I'm observing is normal. If I touch LOAD, then put in a CD, then touch CD it seems to work properly!

I think I've stumbled into a working repair... thoughts?

Hi jonbr,

Yes - this behaviour is normal. Opening the CD door, inserting a CD, then touching the LOAD button will close the door, spin the CD and load the table of contents. The BC9500 displays the available tracks and waits for you to either program a track sequence or just play the whole disc (by touching CD).

Alternatively, once you have inserted the CD, touch the CD control to do all the above automatically (obviously no track programming).

My BC9500 is my most beautiful, logical, well thought-out B&O product that I own.

Lawrence