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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.
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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
- Does the sound always disappear after roughly the same amount of time?
- And does it return again after the unit cools down?
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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.
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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!
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Thank you, that is a very important additional test.
If I understand correctly:
– BCK remains OK
– WS remains OK
– DATA remains OK
– VDDA / VDDD / VDDO remain stable at 5V
– MSUB remains at 5V
– and the analog audio signal disappears directly at the output pins of the TDA1305TThen I agree: this makes the TDA1305T itself the most likely cause.
At this point the problem is probably not the CD mechanism, not the digital signal going into the DAC, not the supply voltage and not the mute line.
The difficult part is finding a trustworthy replacement. Since the TDA1305T is an old Philips/NXP DAC, I would be very careful with Ebay or AliExpress parts. They may be reclaimed, relabelled or fake, even if they look correct.
I would try:
– NXP authorized distributor network
– Rochester Electronics
– professional obsolete component suppliers with traceability
– or possibly a donor board from another known-working unitPersonally, I would avoid buying more “new and original” ICs from unknown marketplace sellers unless they can provide proper traceability.
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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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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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Hello,
today I have bad news and good news.
Bad news: after replacing the TDA1305T, the problem persists.
so you were right, being not convinced that the fault was in said Ic.
good news: the techician tried to cool down dhe PCB32 board after the BS9000 became mute, and the sound came back.
now we have to find out which one is the component that overwarming itself cause the problem.
do you have any suspect?
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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