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

Martin

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TheDane
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Hi again,

Any ideas, guys?

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!

TheDane
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Thank you for reply. Forgot to say, that the mute-relay works like a charm. Everything works, output 1 and 2 and also the headphones output. All input works aswll and also the radio and so on.

Only Thing is, that All output (speaker 1 and 2 and headphone) play sound which start out perfekt only to distort more and more, until it after appr. 10sec. sound like a farting dog, regardless which input/output I choose.

My Best guess is some caps om the preamp board, since I changed caps around the mainpower.

Any ideas?

solderon29
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Verified by TheDane

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

TheDane
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TheDane replied on Tue, Feb 11 2020 10:17 PM

Thanks solderon

C9 and C10 I have replaced as My first effort. I Will try following your instructions and reply when I'm done.

TheDane
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OK, Im back. I have cooled All ICs on the board to appr. - 30 degrees celcius, and the problem persists. I have noticed, that the backup battery may need to be replaced, because it cant memorise when unplugged from 240V. Can this be the problem? It would be Nice if you know, because otherwise I will need to re-cap the entire preamp soon, to be able to seek-n-destroy the fault.

solderon29
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Did the voltage checks around IC4 and 5 reveal anything?

Nick

TheDane
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TheDane replied on Fri, Feb 14 2020 11:00 PM

Hi again

So I made a "diode-test" on every pin on each IC on the preamp. IC 1, 2, 3, 4 and 5 are in perfectly good and operational condition. But-but-but, IC nr. 6 (the TC9184p from Toshiba) was in poor condition indeed. L/R bass-control aswell as L/R treble-control aswell as some other pins seemed to be shorted, when connected to the GND-pin.

I think the TC9184p IC is burned, and this could explain the particular habit of the reciever, that when it plays parts of music, where there might be extra bass or treble, then the sound starts to deteriorate/degenerate even faster. Maybe...

I still cant figure out, why it plays so well the first 2-4 seconds (some times longer), when/if the IC is faulty (even when cooled down to minus 30 degress celcius).

Ok, I think that I will wait re-capping the preamp for now, because if the failure is the TC9184p IC, then I will not obtain better sound quality from my beomaster, before I have replaced the faulty IC either way.

Maybe I can find my sparepart in China somewhere, so it may take awhile before I can write you the result.

TheDane

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

TheDane
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Yes, Im not happy either to buy in China, but it seemed like the only way. All my searches led to China... until you wrote😊 can we PM on this board?

TheDane
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TheDane replied on Sat, Feb 15 2020 10:35 PM

Re-capped the entire pre-amp board anyways. The problem is still there, but I already had a clue that the caps werent the problem, so HEY, COULD ANYBODY SEND ME A NEW TC9184P IC? Cool if you please🤩😋

Sincerely your truly fan forever if you provide me with a Tc9184p IC

The Dane

Dillen
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Dillen replied on Sun, Feb 16 2020 8:06 AM

TheDane:

Re-capped the entire pre-amp board anyways. The problem is still there, but I already had a clue that the caps werent the problem, so HEY, COULD ANYBODY SEND ME A NEW TC9184P IC? Cool if you please🤩😋

Sincerely your truly fan forever if you provide me with a Tc9184p IC

The Dane

You have email.

Martin

TheDane
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TheDane replied on Wed, Mar 25 2020 10:58 PM

Update: I have now replaced the tc9184 (thank you Martin) along with mcp8554 (ic3 and 5), I have Re-capped the entire preamp, Re-capped the powersupply-board completely, teste idel current (10mV both sides), cooling ribs fine, change backup battery.

Problem persists🙄

However, I may suspect the IC4 (Tc9177p) could be faulty, because I found out, that sometimes I can eliminate the problem for 2-3 minuts by turning loudness on and off. And a New fault (which relates to the Tc9177p) has occured, that the bm5500 always powers on at 42 volume and without loudness, No matter how often I set the memory otherwise.

COULD anyone provide me with the Toshiba chip TC9177p?

Best regards

TheDane

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