[KolfMAKER]

Thank you for the update.

Actually, I think this gives us another important clue. The fact that you were able to play two complete CDs without any problems strongly suggests that the laser and CD mechanism are fundamentally working correctly.

When the fault occurs:

• the CD is recognised,
• the disc spins,
• the time counter advances,
• you can change tracks and even change CDs,
• but there is simply no audio.

To me, this now sounds less like a CD reading problem and more like an audio routing, muting or initialization issue.

I have one question that may help narrow it down further: When CD is playing with no sound, could you try the following?

1. Switch to RADIO and confirm that radio audio is present.
2. Then switch immediately back to CD.

Does the CD audio return, or does it remain silent?

 

If switching sources restores the CD audio, that would point towards a source selection or muting problem.

If the CD remains silent even after switching back from RADIO, then we should continue looking around the CD audio path on PCB32.

 

I think this simple comparison could provide a very useful clue.

Location: The Netherlands

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[KolfMAKER]

Thank you, that is important information.

I also have another thought.

A worn laser in a Beosound 9000 usually causes problems reading the disc itself. In that case, you would typically expect symptoms such as difficulty reading the TOC, long “Reading…” times, failure to start playback, or skipping during playback.

However, in your case the CD appears to be recognised correctly, the counter starts normally, and the disc continues playing.

That seems to suggest that the digital data is being read successfully, making a laser problem less likely.

Can you confirm one detail?

When there is no sound, does the time counter still continue to advance normally from 00:00 as if the CD is playing correctly?

If the answer is yes, I think that points even more towards a problem after the data has already been read from the disc, rather than a laser or optical pickup issue.

I still think the key is to compare the “sound OK” and “no sound” situations and determine exactly what changes between those two states.

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[KolfMAKER]

Great!

Out curiosity:

– Which one?

– Picture?

Location: The Netherlands

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[KolfMAKER]

That is an interesting observation, but I am not yet convinced that it is directly related to the CD audio problem.

To me, it sounds more like a separate issue involving the sledge positioning or calibration.

If TM71 always fails because the sledge crashes into the disc in position #2, I would first suspect:

• incorrect home/reference position,
• sledge position feedback (sensor or encoder),
• mechanical alignment,
• or a servo control issue.

The important question is:

Did this behaviour already exist before replacing the LF33CDT, or is this the first time TM71 has been run?

If TM71 has never completed successfully, it may simply be revealing a second, unrelated fault.

On the other hand, if this behaviour only appeared after the recent work, it would be worth checking whether anything around PCB32, its connectors or the servo-related signals has changed.

For now, I would treat the TM71 failure and the intermittent CD audio as two separate problems unless there is clear evidence that they are connected.

Location: The Netherlands

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[KolfMAKER]

Sorry to hear that Edo. The new symptoms actually make the diagnosis even more interesting.

The fact that:

• the CD spins correctly,
• the counter advances normally,
• radio always works,
• and sometimes switching to Radio first and then back to CD restores the sound,

suggests to me that this may no longer be a simple thermal failure.

I now wonder if there is an initialization, muting or power sequencing issue on PCB32.

The replacement of the LF33CDT may have improved the original thermal problem, but there could still be another fault in the same area.

I think it would be useful to compare two situations:

1. Cold start → select CD → no sound.
2. Cold start → select Radio → then switch to CD → sound OK.

In both cases I would check:

• Is the analog audio present at the output of the TDA1305T?
• Is the 3.3V output of the LF33CDT stable (preferably with an oscilloscope, not only a multimeter)?
• Does the muting circuit behave differently between the two cases?

I would also carefully inspect and, if necessary, reflow the solder joints around the LF33CDT, its input/output capacitors, nearby vias and connectors. A marginal solder joint or via could easily explain why the behaviour changes after source switching.

The good news is that the investigation now seems to be focused on a much smaller area than before.

Location: The Netherlands

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[KolfMAKER]

I do not recognitie it as a B&O part, but it might still be one. Looks to me as something that is to be pushed in some kind of frame (with the 4 upstanding feet). And keep two cables/wires apart from each other on both sides.

If you have some extra pictures from different angles, my Ai-part finder might help.

Location: The Netherlands

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[KolfMAKER]

Hi Martin,

Can you upload mor pictures, of all sides?
And add the dimensions?

Best,
Ernst

Location: The Netherlands

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[KolfMAKER]

That is excellent news! Congratulations on finding the real fault.

This has turned out to be a very interesting troubleshooting case.

In hindsight, the LF33CDT explains many of the symptoms. A regulator can become thermally unstable without completely failing, so measuring a nominal voltage with a multimeter does not necessarily mean the supply is healthy. Small voltage dips, oscillation or excessive noise can easily upset the DAC and surrounding circuitry.

I think your systematic approach deserves credit:

• Verifying the digital signals,
• Replacing the suspected DAC,
• Using thermal testing,
• And finally narrowing the fault down with freeze spray.

Thank you for taking the time to report the final solution. Threads like this become very valuable for other Beosound 9000 owners who may encounter the same problem in the future. Great info for the community!

Enjoy your rescued & fully working BS9000!

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[KolfMAKER]

Thanks for sharing again Edo. This is actually the most promising clue so far.

What caught my attention is that cooling the LF33CDT does not just bring the sound back temporarily, but appears to extend the operating time before the fault occurs. That makes the LF33CDT a much stronger suspect than the components investigated earlier.

Since the LF33CDT is a 3.3V regulator, a thermal problem there could potentially explain many of the symptoms observed so far, including why the DAC initially appeared to be the culprit.

If I were troubleshooting this, I would not only replace the LF33CDT, but also:

• Inspect and reflow its solder joints,
• Measure its input and output voltages before and after the fault,
• Monitor the 3.3V rail while the unit warms up,
• Check whether the output voltage changes when the regulator is cooled.

At the moment, this seems like the strongest lead you have had so far. Please keep us updated after the replacement.

Location: The Netherlands

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[KolfMAKER]

Great to hear you have practical helping hands to support you. Good for you!

For the interest of others reading this topic, please come back when your issue has been resolved. And ask your friend to write a short summary of the cause and how he solved it.

 

Location: The Netherlands

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[KolfMAKER]

Thank you, the photos help understanding.

A few things are still unclear to me:

1. During your test with the Pioneer headphone output, approximately where was the volume control set?
   Very low, medium, or normal listening level?
2. For your tests, did you put the  small switch on the bottom of the BeoLab 8000, to the lower position (LINE – see picture) when using the RCA input: yes/no? (The speaker may not work correctly from the RCA input when the switch is in the PowerLink position)
3. Can you connect the working BeoLab 8000 using exactly the same setup:
   • same Pioneer amplifier
   • same cable
   • switch in the lower (LINE) position
   • same volume setting
   • Can you share the results of this check?
4. Also, when the faulty speaker LED is green, do you hear absolutely nothing at all?
   No hiss from the tweeter, no hum, no clicks from the drivers?

This information will help narrow the fault down considerably.

 

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[KolfMAKER]

Hi Christian,

One important question that may help us narrow this down: How exactly are you testing the speaker?

Are you using:

• PowerLink from a B&O source?
• The RCA input?
• Something else?

You mentioned that the LED turns green when you power the speaker on. Does it also stay green while music is actually playing?

Knowing how the speaker is being driven is important, because it helps us determine whether the amplifier is receiving an audio signal at all, or whether we should focus on the audio input stage first.

The fact that the LED goes green and the relay clicks is still encouraging, as it suggests that a large part of the electronics is functioning normally.

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[KolfMAKER]

Thanks Christian, for posting the photos.

I don’t immediately see any obviously burnt components, damaged tracks or leaking capacitors, which is hopeful. Before measuring anything complicated, can you tell us exactly what the speaker does? (When connected via PowerLink/Line-IN and starting music):

• Does the LED stay red permanently?
• Does it change from red to green when a signal is present?
• Do you hear any clicks from inside the speaker, when music is started?
• Does the other speaker still work normally?

Let us know your findings.

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[KolfMAKER]

Hi Christian,

The fact that the red LED still comes on is actually encouraging. If the main fuse had completely blown, I would normally expect the speaker to be completely dead.

Since the speaker was accidentally connected to 220V while still configured for 110V, I suspect the standby power supply may still be working, but another part of the power supply could have been damaged.

My suggestion would be to start with the basics:

• Check the mains fuse with a multimeter (power disconnected).
• Post clear photos of both sides of the power supply board.
• If you are comfortable using a multimeter, measure the secondary supply voltages coming from the power supply.

Also, did you hear a pop, smell anything burning, or see any smoke when it happened? And does the other speaker still work normally?

Those details may help narrow down the fault considerably.

Good luck, and don’t give up on them yet — the fact that the LED still lights up is a positive sign.

Location: The Netherlands

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[KolfMAKER]

I would not worry too much about the 4-layer PCB at this stage.

Yes, an internal track or via failure is possible on a multilayer board, but based on the symptoms I do not think it is the most likely explanation yet.

The reason is that you already have several strong clues pointing towards a localized thermal issue:

• cooling around C401/C403 restores the sound,
• replacing C401/C403 did not solve the problem,
• TR405 starts oscillating when the fault occurs,
• the behaviour is repeatable and temperature-dependent.

To me, that still sounds more like a component, solder joint, via, regulator, transistor or local control circuit problem than a hidden internal PCB track.

I would wait for the proper freeze spray and continue narrowing down the exact area by cooling individual components one at a time.

In particular, I would focus on:

• TR405,
• components directly connected to TR405,
• nearby capacitors, resistors and diodes,
• and any ICs or regulators in the same section of PCB32.

Only if the freeze spray testing fails to identify a specific component or area would I start considering an internal PCB defect as a more likely possibility.

At this point I still think there is a reasonable chance that the actual fault can be isolated and repaired.

Location: The Netherlands

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[KolfMAKER]

Hi Edo, thanks for your update.

I actually think this is progress. The fact that replacing the TDA1305T did not change the behaviour strongly suggests that the DAC itself was not the root cause. What I find more interesting is that:

• cooling around C401/C403 restores the sound,
• replacing C401/C403 did not solve the problem,
• and TR405 starts oscillating when the audio disappears.

That makes me wonder whether C401/C403 are simply close to the actual faulty component, rather than being the fault themselves.

At this point I would focus on TR405 and the components directly around it. It may be useful to measure the base, collector and emitter voltages of TR405 before and after the fault occurs.

Once the freeze spray arrives, I would also try cooling TR405 and the surrounding components individually rather than cooling a larger area of the PCB. To me, TR405 and its local circuitry now look like stronger suspects than the DAC.

Location: The Netherlands

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[KolfMAKER]

Hi edo,

That is actually very useful news! If cooling down PCB32 brings the sound back, then the problem now looks clearly thermal and the TDA1305T itself is much less likely to be the root cause.

My first suspects would be:

• voltage regulator(s) on PCB32,
• electrolytic capacitors around the DAC / audio supply section,
• local decoupling capacitors,
• mute / output stage transistors,
• bad solder joints or hairline cracks,
• possibly a clock/buffer component around the DAC section.

 

Suggested steps:

I would not cool the whole board anymore, but use freeze spray very locally, component by component.

Start with the power regulators and capacitors around the DAC/audio section, then the muting/output stage components, and finally any logic/clock components feeding the DAC.

Also, it may be worth checking the DAC supply rails again with an oscilloscope, not only DC voltage. A regulator or capacitor can still show 5V DC while having noise/ripple or instability when warm.

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[KolfMAKER]

Good luck!

🤞🏻

Location: The Netherlands

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[KolfMAKER]

That sounds like a reasonable approach.

As far as I know, there are no known Beosound 9000-specific versions of the TDA1305T. The TDA1305T is a standard Philips DAC, used in many different audio products of that era.

Therefore, if:

• the donor DAC board is working correctly,
• the donor TDA1305T is healthy,
• the IC is removed without damage,
• and it is soldered correctly onto the BS9000 board,

then I would expect it to work in the Beosound 9000 as well.

What makes your case particularly interesting is that the replacement will also act as a diagnostic test.

If the donor TDA1305T works normally and the fault disappears, that would strongly confirm the original DAC was defective.

If the donor TDA1305T shows exactly the same behaviour as the original IC, then I would start to suspect that something else around the DAC stage may still be contributing to the problem.

In any case, using a known-working donor IC from a complete DAC board gives a much higher level of confidence than buying loose ICs from unknown marketplace sources.

Please keep us updated on the result after replacing the TDA1305T with the donor board one.

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[KolfMAKER]

I think purchasing the complete DAC board was probably the best decision at this point.

After all the measurements, the diagnosis now seems much clearer:

– digital data signals remain present,
– clocks remain present,
– supply voltages remain stable,
– mute line does not change,
– CD mechanism continues operating correctly,
– but the analog signal disappears directly at the DAC outputs.

That combination now strongly points to an internal DAC failure.

Also, the fact that one replacement IC worked briefly before failing could indeed suggest reclaimed, marginal or counterfeit parts.

Using a complete donor DAC board is a much safer approach because it also eliminates possible uncertainties regarding soldering, surrounding components and PCB-related issues.

Please keep us updated — this has become a very interesting diagnostic case.

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