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.

Tanks for your opinion and suggestios.

Is not the first time I check the TM71, and it always went fine.

Just the first times, when i tiried this test, I haven't readen that the position #1 must be without the CD; once learned this, this test never gave me any problem.

I try to remember that the last time I did test TM71 was after the replacement of TDA1305T, and went fine.

Me too I'm thinking that TM71 fault and intermittent audio are due to different reasons.

The strange thing is that sometimes the CD works perfectly, even for hours, and sometimes works with absolutely no sound.

 

 

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.

Hello, in response to your question, yes, the time counter still continue to advance normally from 00:00, even in case of no sound.

That's incredible,

with the BS9000 at home, linked with Beovision7 and Beosound5 via master link, as usual, this morning the CD worked fine; I have listened to 2 whole CDs.

After lunch, I turned on again the CD, and it worked, but no sound at all.

As usual, the CD was spinning and the time counter advancing. I changed track and CD, but always no sound.

I really I don't know what to think.

HAve a nice weekend

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.

Hello, I did the test you suggested me, more times.

When I turn on the CD, i have no sound; switch to radio and it works; come back to CD and again, no sound.

What is happening now is that I turn on the CD, and there is no sound, if I let the CD go, after some minutes, the sound comes out, and goes on....

This is actually a very significant new observation. The behaviour has changed from: “the sound disappears after some time” to: “there is no sound at first, but if I let the CD continue playing, the sound appears after a few minutes and then remains stable.” To me, that points much more towards a temperature-dependent analogue circuit than a CD reading or source selection problem. The fact that:

• the CD is recognised immediately,
• the time counter runs correctly,
• tracks can be changed,
• Radio works normally,
• switching Radio → CD does not restore the sound,
• but simply waiting does,

suggests that some part of the audio circuitry only starts working once it has warmed up. At this stage I would try the opposite of freeze spray. Instead of cooling components, I would carefully warm individual suspect components or small areas (for example with a hot air station set to a low temperature or a hair dryer from a safe distance). If warming a specific component causes the sound to appear much sooner, that would be a very strong clue. I would start with the area around the LF33CDT, TR405 and the surrounding analogue circuitry on PCB32, since that area has already shown temperature sensitivity during your earlier tests. One additional thought: although the LF33CDT has been replaced, I would still verify the 3.3V rail with an oscilloscope during the first few minutes after power-up. Since the earlier thermal tests pointed to this area, it would be useful to confirm that the regulator output is not showing excessive ripple, oscillation or instability while the unit is warming up. It would also be worth carefully inspecting the solder joints and nearby components around the replacement regulator.

Hello,

some days ago I went to my repair boy to take my BS9000 at home, perfectly functioning (this said the technician).

He was right, the cd now works properly, and the audio, by the earphones plug is perfect.

He did just replace a capacitor (not reported in the diagram into the mkIII service manual) (!!!) to fix the problem.

But he had not the possibility to check the master link plug; I did it at home and now the sound is present, but at a very very low volume.

He now suggest to replace ALL the capacitors in the PCB 32 board (about 30), having them 25 years of working behind them.

We will do that, as soon as we  have procured all the capacitors, and I will let you know.

I'm thinking that this will be the right time.

See you

Ik zou het vriendelijk formuleren, maar hem wel adviseren om vóór een volledige recap eerst nog een paar gerichte metingen te doen. That is good news regarding the original CD problem, but I would personally hesitate before replacing all ~30 capacitors on PCB32. The fact that CD audio is now perfect through the headphone output suggests that the original CD/DAC audio problem has actually been solved. The remaining problem now seems much more specific: CD audio is present through Master Link, but at a very low level. Before doing a complete recap, I think a few checks could help narrow this down:

• Which capacitor did the technician replace to solve the original problem? Its value, location and what circuit it is connected to would be very interesting, especially since it is apparently not shown in the MK3 service manual.
• Does RADIO still play at normal volume through Master Link while CD is very quiet?
• Is the low CD volume the same through both the BeoVision 7 and BeoSound 5?
• Can the technician trace the CD audio signal from the now correctly functioning CD/DAC section towards the Master Link circuitry and find where the signal level drops?

Especially if RADIO has normal volume through the same Master Link connection while CD is very quiet, that would suggest that the Master Link connection and at least much of its circuitry are working correctly. I would therefore try to locate where the CD signal loses amplitude before replacing every capacitor. There has already been quite a lot of rework on PCB32, and replacing another 30 SMD components on a multilayer board also introduces some risk of damaged pads, vias or new soldering problems. So my preference would be: diagnose first, then replace components selectively. And please let us know which mysterious capacitor finally solved the original problem — that may be one of the most useful findings from this whole repair!