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Beomaster 5500 sound slowly degenerates over 10 seconds

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TheDane
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TheDane posted on Fri, Jan 24 2020 12:35 PM

Hello out all you fellow B&O enthusiasts :)

Thank you for this amazing board, and all there is to learn hereBig Smile

I post this, because I have this problem with my newly bought beomaster 5500.

Everything works flawlessly and the sound is absolutely amazing with my beovox 4702! But recently at has begun to degenerate the sound over a matter of 5-10 seconds, until an almost complete silence at the end. The degeneration at first sounds like a bit of distortion, then it gets worse and worse until it only sounds like a lazy dog farting (sorry for my language use hereStick out tongue)

I can keep the degeneration away by adjusting the volume up and down 1 step at a time, adjusting balance, adjusting bass or treble setting. but the same moment I lay the remote to rest, the sound starts to degenerate.
The exact same failure occur in the head-phones when plugged, and with the exact same sound-degeneration.

What I have done so far:

- Checked the cooling ribs, and they are fine. Not heated.

- I measured resistors in the amp-section, and they are within specs.

- I changed the 22nF and two 10nF caps placed at the power-supply to new ones.

- I have unmounted the accessplate under the beomaster and visually inspected everery soldering

None of this gave any results nor hints of what to do!

Could it be the mute-relay/phone-relay?

No-one has ever described this kind of failure in a beomaster, so I am in a bit of a confused state right now...

Please, any advice is welcome Cool

Best regard, TheDane

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Guy
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Answered (Verified) Guy replied on Mon, Feb 10 2020 9:25 AM
Verified by TheDane

You can rule out the mute relay by connecting your speakers to the Speaker 2 sockets, as these are not fed via the relay.

My only other suggestion is adjusting (or replacing) the idle current trimmers - but that is very much a guess based on reading about the problem of other 5500s!

solderon29
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Check the voltages around the preamp i.c's IC4(TC9177)and IC5(4558)particulary the +12/-12 lines(pins 4 and 8 on IC5)

The fact that both channel's are affected suggests something in common such as psu?

TC9177 could be faulty,I have seen this.Do you have any freezer spray to try,to see if temperature shifts will provoke a return to normal service?

C9 and C10 (near IC5)can be troublesome too.

Nick

Dillen
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Answered (Verified) Dillen replied on Sat, Feb 15 2020 7:53 AM
Verified by TheDane

Buying from China = risk of receiving counterfeit components.
Ask Littlediode in the UK - or me.

Martin

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Dillen
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Dillen replied on Fri, Apr 17 2020 10:07 AM

Backup battery OK?
The Beomaster can do all kinds of strange things, if the backup battery is bad.
It can also lose or mess up settings  - also option settings (remote control = option 1).

Martin

TheDane
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Yes, its brandnew, measuring 3.05V. It all worked the whole day, yesterday, after my rapair on the preamp was overhaued and the new battery was installed. No problems. I also unplugged the BM, and plugged it again yesterday, and evereything worked (all but the memory-settings, which I planned on looking after today)

Do you think it could help replacing the 8031 IC? Or could it be the eeprom?

Kind regards

TheDane

TheDane
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Hey Martin (and other capable tech-oracles Big Smile)

While I am waiting for my spareparts for the microprocessorboard in the BM5500 to arrive, I wondered:

Question: If the change of backup battery messed up some things e.g. the option setting, so that settings switched to "no remote", will I then ever be able to recover the microprocessorboard (You know when I replaced caps, microprocessor i.a.)? And will I ever be able to use a beolink with this particular pcb4 again?

Or am I fooling myself here?

Humble questions
Lars

Dillen
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Dillen replied on Mon, Apr 20 2020 9:39 PM

Yes, the Beomaster still listens to remote commands, it just doesn't respond to anything but option changes.
Press Sound-1-Store on the remote.

Martin

TheDane
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TheDane replied on Mon, Apr 20 2020 10:35 PM

Ok, I Will try that, when i replaced some parts. For now, that trick doesnt work, either in stdby, nor powered on. Also the Tp4 doesnt work, the display only keeps flickering when shorted, which could indicate a worn out 33uf cap, or a fried microprocessor (I guess?) 

Pindsen
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What was the end of this story?

/Pindsen

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