B&O Beosystem 2500 (type 2606): CD not recognized

On my workbench is a B&O Beosystem. The symptoms are: CD is not recognised, CD won’t start spinning.
In most cases these machines have worn belts for the glass doors, CD cover and tape deck. Most also have doors that need adjustments. This one was no exception, but I discovered that the CD was also not working. Let’s see what is going on:

To understand where to look for the defect, we need to know the steps it is going through upon initialisation. The steps are for most CD players the same, except for the start of the spindle motor that turns the CD. In some cases the motor is started in the early phase, but mostly when a cd is “seen” by the laser. That is: laser light is reflected onto the CD and picked up by the laser pickup sensors.

The steps are as follows:

  • When CD tray/door is closed
  • Move Laser to starting position*
  • Turn on laser light
  • Start focussing sequence (Depending on system, repeat this several times, sometimes move the laser tracking position.
  • When CD is detected, start spindle motor.
  • Look for lead in track and read TOC (Table of Contents)

*) Linear tracking and radial tracking servos move the laser to the start position when this process is started. That is not the case when motor/gear tracking systems are used. With that system the laser is mostly moved to the beginning of the CD upon power on, upon CD tray close/open and upon stop command.

Focus sequence not working

With the knowledge of these startup steps I started to test the system with and without a CD in the player. The spindle motor was not started and the CD was not recognised.
Without a CD in the player, I could see whether the laser tries to find a CD and tries to focus on it. That wasn’t happening at all, also the laser was not moved to the center of the CD. So that makes sense that the CD is not detected. I know that this Philips based system uses no feedback on laser light “on”, so it would try to focus anyway regardless of whether the laser is on or not.

After I mechanically loosened the CD cover, I could safely try to confirm that the laser in deed was working. Gently because I didn’t want to damage my eyes. I had a quick look at the laser from a distance and from an angle while keeping the laser in the shadow of my hand. A little faint red dot was enough for me to see and know that the laser was fine.

Measurements

I started to see whether there is any voltage on the tracking and focus servo, there was nothing on there.
Next I checked the schematics to see how the tracking and focus servo are driven:

Focus and Tracking servo schematics

There is one half of a dual opamp used for driving the focus servo, the other half for the radial tracking servo. I first checked the positive and negative power lines, both were not present. In the schematics the negative power line is pictured on the focus servo opamp, the positive is on the tracking opamp. Both power lines have 1 Ohm safety resistors. Those were both defective. That was not directly visible on the resistors as shown in this picture:

As a precaution I removed and replaced four of those resistors. Then it showed that at least one had been a bit to warm.

New resistors installed

And the CD is working again!

To see whether the laser current is still within specifications, I looked up the procedure in the service manual. The voltage should be measured over R16, which is a SMD type resistor.

The voltage was perfectly within specs, so no need for adjustment.

8 comments on “B&O Beosystem 2500 (type 2606): CD not recognized

  1. Hi Mark
    I found your guide very useful to identify the problem of my Denon CD Player UCD-F88 (part of the UPA-F880 system) spindle motor that doesn’t start running.
    In the first place I tought it was an error from some sensor, since the player had a misaligned feed and frame, so the door won’t close correctly, and i had to disassemble and reassemble the unit. Then I had a problem with a sliding feed motor belt, that was been probably overheated and deformed by the motor’s spinning in it, since the feed slot was blocked.
    Now, my problem is that a service manual for this unit seems to be unavailable, and, despite of the really clear main board ID for every component, jumper and voltage, I can’t understand how to check the laser lead in return and motor input voltage (on its connector is 0)…
    Could you help in any way?

    • Hi Luigi,

      For what I can tell based on a Google search for that cd player, it’s pretty different in comparison with the B&O cd system.
      I think the Denon is built on a Sony assembly, don’t know what type it is exactly. KSS213 or KSS240, I would guess.
      When you move the laser assembly to the middel of the slide and then power up the player, does it then move towards the spindle motor?
      If that works, then you can be sure the tracking motor circuit is working.
      Next is to check the spindle motor, but with most Sony systems the spindle motor only starts after a cd is “seen” by the laser. So laser control, focus and laser pickup signals should work.

      Kind regards,
      Mark

  2. My beosound 2500, while playing a CD there is a poping sound/ cracking sound. Plz help how to resolve it. Thanks

    • Hi Atif,
      It’s very difficult to pinpoint what is causing this sound from a distance. Does it happens all the time? Or only when the beosound is cold? What have you tried to resolve the issue? Does the CD turn freely when the CD door is closed? You can try if the problem gets worse or not when you lay down the beosound on its back or tilt it that way.

      Kind regards,
      Mark

      • Hi Mark,
        Thanks for the reply.

        Does it happens all the time?
        YES THIS HAPPENS ALL THE TIME.

        Or only when the beosound is cold?
        NO… same response all the time.

        What have you tried to resolve the issue? Show it with one mechanic… but he is not a B&O expert… but he tried some flukes but nothing happend.

        Does the CD turn freely when the CD door is closed?
        Every thing works perfect except this cracking sound… Recognize CD, change tracks…. I mean every thing works fine but the POPING or CRACKING SOUND

        You can try if the problem gets worse or not when you lay down the beosound on its back or tilt it that way.
        I have tried but no change same problem…

        Plz help how to fix this… or is there any specific laser lens no. for this CD player? so we can change the lens or any thing else?

        Many Thanks & Regards,

      • Hi,

        Those B&O systems have different cd player systems installed over time. The older (better) ones were the CDM4 laser units (swing arm) with TDA1541A DAC board that is located on the right side of the system (behind the shiny black cover).
        That is the one that is shown here in the images. The other one is a CDM12 kind of laser unit with a control PCB at the back of the laser unit. These are not so great to repair.
        When you have the version with the CDM4, then it’s most likely never the laser unit. These are extremely reliable. The crackling/poping noise could be related to the DAC or Oversampling chip, or its power supply.
        Check the -15V and -5V signals to the TDA1541A. Are they stable and have little ripple on them?
        If you have an oscilloscope available, play a test CD with pure sine wave, 1kHz is commonly used. View this on the scope and look at the shape of the crackling/poping noise. That could point you to the cause of the problem.
        With the CDM12, you never know what is causing the issue. Sometimes you could replace the complete laser assembly with laser and motors, but it’s hard to get one that is actually new. I see lots of reused motors and “new” lasers fitted into them… 🙁

        Hope this helps you a bit.
        Kind regards,
        Mark

  3. Hi Taraus25,

    Sorry for the delay in my reaction. Somehow I didn’t get a notification.
    In most cd-players the spindle motor wil only start if the laser light is reflected on the disc and detected by the pickup.
    I have never seen a damaged spindle motor before that is completely dead, so to me that’s highly unlikely. In cases where the spindle motor is defect is that it does not run fast enough or is unstable due to worn bearing.
    The following sequence of steps is the best way to troubleshoot:
    1. Check if laser tracking servo moves the laser to the center of the CD
    2. Check if laser is emitting
    3. Check if focus lens is moving
    4. Check the voltage from the spindle motor driver to the motor

    If step 4 fails, it might also be the laser current that needs adjustment (Only with CDM swingarms, not with CDM12 in later BeoSounds.)
    The service manual also states that the laser current needs adjustment after replacing the laser. Remember that for the best adjustments you need a reference disc that meets Red Book specifications.

    Kind regards, Mark

  4. My beosound 2500 after changing the laser still could not work. Understand the issue is not just the laser lens but the spindle motor could not spin the disc . Does this mean the spindle motor is damaged and need replacement ?

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