I am not fully convinced yet that the TDA1305T itself is the root cause. The fact that the CD keeps spinning and timing continues, while only the audio disappears after 1-2 minutes, could also point to a thermal issue, power supply instability, muting circuit, soldering problem or an issue around the DAC/output stage. Also, the different behaviour with the replacement IC’s does not automatically prove they are fake. One important question: Which version of the Beosound 9000 is this exactly? MK1, MK2 or MK3? There are differences between revisions/boards and that may matter here. Do you know: - the exact type / MK version? - whether the service manual matches this unit? - if the supply voltages around the DAC were measured when the sound disappears? - if the mute signal changes state when the audio drops out? To me this still sounds more like a surrounding circuit issue than a pure DAC failure.

Hello, sure I know which version of Beosound 9000 I have; is a Mk3 (type n. 2571). We are consulting the BS9000 MK3 service manual. Thanks for your opinion, I'll send it to the technician. Any other suggestions will be appreciated. Kind regards    

Thank you, that information helps. Since it is a MK3, at least we know the technician is working with the correct service manual and the correct DAC type (TDA1305T). However, the behaviour still does not fully convince me that the DAC IC itself is the primary problem. The fact that:

• the CD continues spinning correctly,
• timing continues normally,
• and the audio first becomes intermittent before disappearing,

still sounds more like a thermal or surrounding circuit issue to me. Possible areas worth checking:

• power supply stability around the DAC/audio section,
• voltage regulators,
• electrolytic capacitors,
• mute circuit/transistors,
• solder joints or hairline cracks,
• temperature-sensitive components around the DAC stage.

Especially because the failure develops after some operating time. A useful diagnostic step could be freeze spray / controlled heat testing around the DAC and surrounding circuitry to see if the behaviour changes immediately. Questions

1. Does the sound always disappear after roughly the same amount of time?
2. And does it return again after the unit cools down?

Hello, let me correct you: the issue with the original Ic TDA1305T is that in 1-2 minutes the CD audio becomes mute, the CD keep spinning and the timer goes on while with other sources (radio, n. radio, n. music) there are no problems at all. Individuated the Ic TDA1305T as the responsable of the issue by the technician, I providet to buy on Ebay n. 2 spare parts (original and brand new, they said). When arrived, we replaced the original IC with a new one: we tested functioning, and after abour 30 sec. the cd signal became intermittent, then disappeared. So we replaced the new Ic with the other new Ic; testing functioning, we had no sound at all. Finally, we replaced the Ic with the original one, and everything came back the same as before (soun disappear in 1-2 minutes). So we had 3 different responses by 3 different Ic's. What do you thingk about that?

Thank you, this clarification is useful. What I now think is: The fact that the original IC always returns to exactly the original behaviour probably means: - the board itself was not permanently damaged during the IC replacements, - the original fault is still present in the same signal chain, - and the Ebay IC’s may indeed be questionable, but they still do not automatically prove that the original DAC IC is the root cause. The 3 different behaviours with the 3 IC’s are interesting: - original IC → sound disappears after 1-2 minutes, - replacement IC #1 → intermittent sound after ~30 seconds, then mute, - replacement IC #2 → no sound at all. This could mean: - the replacement IC’s are fake / reclaimed / defective, - or they are more sensitive to an existing surrounding circuit problem. At this point, I personally would not continue buying more TDA1305T IC’s before doing more measurements around the original IC. I think the important next diagnostic step is determining: Does the audio already disappear directly at the analog output pins of the DAC, or only later in the muting/output stage? That would help confirm whether the DAC itself is really failing. I would suggest checking: - DAC supply voltages before and after audio disappears, - BCK / LRCK / DATA signals, - mute line / muting circuit, - analog output directly on the DAC pins, - freeze spray / thermal testing on the DAC and surrounding components. To me this still feels more like a surrounding circuit or thermal issue than a confirmed pure DAC failure.

Thank you a lot; I will send your post to the technician and I'll update you on what will happen. Kind regards.

Goodevening, today with the tachnician we check these line: pin: 4. BCK -> Signal ok 5. WS -> Signal ok 6. Data -> Signal Ok 19. MSUB - > before and after audio stop remain on 5v 1. VDDA - > 5v, before n after 10. VDDD -> 5v, before n after 28. VDDO -> 5v before n after.   Technician reamin on idea that the issue is the DAC.

Thank you, that is useful information. If BCK, WS and DATA remain OK, and VDDA / VDDD / VDDO all remain stable at 5V before and after the audio disappears, then the digital input signals and supply voltages to the TDA1305T seem to be present. That does make the DAC a stronger suspect than before. However, I think there is still one very important measurement missing: Is the analog audio signal still present directly at the output pins of the TDA1305T after the sound disappears? If the analog output from the DAC disappears while BCK / WS / DATA and all 5V supplies remain OK, then I would agree that the DAC itself becomes very likely. But if the analog signal is still present at the DAC output pins, then the problem must be after the DAC, for example in the muting circuit, output stage or coupling components. So in my opinion the next decisive test is to check the analog output directly on the DAC pins before and after the fault occurs. Let me know the outcome!

Sorry, I missed to tell you about this test, that we already have done: The result is that when the sound disappears, even the analog audio signal disappears at the output pins of the TDA1305T . At this point, I think we have no more any doubt regarding the need to replace the TDA1305T to fix the problem. As you already know, we already tried to replace the original DAC with other two, that I have purchased on Ebay, and, no obstain the Ic's were guaranteed as "original" and "brand new", noone of them, once mounted, werk properly. Do you know any reseller of electronic components who could sell me a truly original and brand new Ic? Thank you a lot for your precious cooperation