Searching for a spare part (ic for Beosound 9000

[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

Favourite Product: BeoSound 9000

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[edo69]

Hello, I begin to have some doubts regarding the possibility to repair the PCB32.

Right today, I have readen that the PCB 32 is a multi-layer board (4 layers); do you think that the issue could be in an internal conductive track?

In this case, we can not check nor repair internal tracks.

[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

Favourite Product: BeoSound 9000

My B&O Icons:

[edo69]

Hello,

finally we had the possibility to test PCB32 components with the cooling spray.

the result was that the sound remains for more time cooling the LF33cdt.

So we will buy some and we will replace it in 2 weeks, ’cause the technician is going to holidays.

I will let you know…..

[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

Favourite Product: BeoSound 9000

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