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 TDA1305T

Then 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 unit

Personally, I would avoid buying more “new and original” ICs from unknown marketplace sellers unless they can provide proper traceability.

Unfortunately noone of these suppliers you suggested have the TDA1305t in stock.

I also tried with 12 other sellers, such as: Mouser, Farrell, Tme, etc. and noone had avaliability.

So I decided to purchase an entire DAC board with n. 2 TDA1305T inside, on www.audiophonics.fr; I will keep you updated

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.

Hello,

unfortunately the DAC board I have found on www.audiophonic.fr is not the same mounted on Beosound 9000; It is only used to disassemble one of the two Ic TDA1305T and replace the original one with it.

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.

Hello,

the board with the two TDA1305T is jusr arrived.

The day after tomorrow we will replace it and I will let you know the result.

Good luck!

🤞🏻

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.

Hello

Thanks again for all your help.

The issue is increasingly complex.

As you already know, after replacing the Ic TDA1305T, the issue is still present.

These are today's updates:

First of all, we were unable to find a can of spray cooler, so we did the test with a can of simple compressed air.

We ordered the spray cooler online, and it will arrive soon.

In the meanwhile, we noted that cooling the capacitor C403, the sound come out back; we replaced it, but nothing changed.

Then we replaced the capacitors C401 and C403, 'cause even cooling them, the sound come out back. But the problem persists.

We noted that wnhen the sound disappears, the TR405 output voltage starts to oscillate (from 3,08V to 3,22V, more or less), but we did not find what C403 got to do with TR405 .

So we are taking a pause due to the arriving cooler, that will allow us to make more accurate tests.

That's all for the moment.