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Beomaster 8000 Channel distortion (SOLVED)

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hamacbleu
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hamacbleu posted on Thu, Aug 1 2013 11:43 AM

Hi to all,

My Beomaster 8000, which has been unfaulty and perfect since 3 months now, displayed yesterday some strange behaviour. The right channel (which has never displayed any faults at all) has now a lot of distortion in the low frequencies. This is most apparent as I turn the volume up.

-Caps and trimmers are all new

-It is not caused by the speaker switch

-It is not caused by the speaker

-When using the headphones, I don't hear that problem

With my past experiences, and having learned from some of you, i'm suspecting a crack solder joint somewhere on the output board. (It's getting old and hot in there because of the power supply). Or could it be the yellow output wire to the speaker that can be loose since the sound from the headphones appears to be fine?

 I'm confident I'll rule this problem out easily, even if i'm nervous to open that thing again, but does anybody has experienced the same thing before and what was your solution? For now, I'll check in the next few days if it's intermittent or not...

Thanks!

Guillaume

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Dillen
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hamacbleu:
(It's getting old and hot in there because of the power supply).

What's wrong with the power supply since the amplifiers get hot ?

Martin

chartz
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chartz replied on Fri, Aug 2 2013 10:40 AM

What gets hot in mine is only the display circuit!

The amps hardly ever get more than lukewarm.

My guess is a contact/solder problem of some sort. Trace the signal!

Jacques

Jacquesboo
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My came back from servicing with the same problem !

Sorry but my technician is in holyday during august and will work on it again in september to fix the problem. As he test all the electronic part of the amp (everything seems to be perfect), I think it could come from speakers socket (they are quite loose in my BM).

Do someone know if there is a separate amp for headphone in the BM8000 ?

I'm interested to know if you find a solution. When I will fix the problem, I will also post the answer.

BR,

Jacques

 

hamacbleu
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Thanks to all,

No, the amps are not getting hot at all. I just meant that since the power supply and display circuits are just below and above the right output amplifier, maybe that the board ages more badly than the other side. After a few hours, its getting somewhat warm above the display fins... as a comparison, It appears to me the the heatsinks of the amps, after the same time spent, seems to display much less heat that these ventilation fins...

Yesterday I let the amp plays and tried to understand what was happening. The distortion occurs at about 3.8 and up, and only if I turn the encoding wheel real fast. if I go slowly, it's stays fine.

My assumption is a broken solder joint or, a failing transistor.... But if it would be a failing output transistor, wouldn't the sound be distorted too in the headphones output: it's not... (when the speaker switch is off)

Probably a broken solder joint: I don't know how time this machine spent in a box before I acquired it. Now that I use it frequently, maybe weaknesses starts to appears. And it's probably not the only one I'll met...

I'm not ready to open it yet but I will post photos and explain what I've done on his thread when I'll do it.

Thanks to all...

To Jacquesboo: from what I understand, the output for the headphones comes from the same source but it probably drives much less power than a speaker. (Please, somebody, correct me if i'm wrong!)

Guillaume

 

Step1
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Step1 replied on Fri, Aug 2 2013 12:10 PM

Is that channel louder than the other channel when distorted? Sounds like a funny fault! Maybe you don't get it in your headphones becuase they don't have the range, or perhaps because they are not loading the amplifier - try headphones at same time as speakers if you can isolate the sound from each...?

Olly

hamacbleu
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Step1:

Is that channel louder than the other channel when distorted? Sounds like a funny fault! Maybe you don't get it in your headphones becuase they don't have the range, or perhaps because they are not loading the amplifier - try headphones at same time as speakers if you can isolate the sound from each...?

 

No, they are at the same level... When I put it to spec 3 months ago, I've put the offset outputs dead down to 0V. Both channels shows now, after a 1 hour run, 6m V. Not that bad I suppose, maybe a little above the prescribed 5m V, but it does not seem to be the problem.

As for testing with the speakers on, it's really hard to tell since I hear the distortion coming from it at the same time. I'll try with the speaker against the wall with a cushion in front of it! But I suppose it will be distorted since it's loading from the same source?..

...Just saw in the technical manual that Jacques posted a few months ago a whole chapter on "supression of noise spike from the volume control" Maybe it will lead me somewhere..

hamacbleu
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...Hmm that chapter leads to the preamp.. I haven't changed these caps... but if it would be the case, the sound would be distorted too in the headphones isn't it..?

Guillaume

hamacbleu
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Just came back from work in hope to make some test with headphones, as mentioned by Olly...

Of course, I can't make any test... the problem has completely disappeared !

It reminds me of my cdx that was only working above 21 celcius.. until I reflowed every griplets

I'll have to open that thing again someday, probably a solder joint of one of those two #$%$# BF857, or that row of resistors.

I'm happy however it's not the left output amplifier as i'm a "Beomaster 8000's left side" hater...

Thanks to everyone for your inputs

I'll keep you informed of the progress

Guillaume

hamacbleu
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The problem becoming more permanent, I decided yesterday to have a look at the right output amplifier. With a magnyfing glass, I was happy to find some joints that would soon become problematics... I reflowed them  and check for their good continuity afterward...

Sadly however, the problem is still there. I noticed that if at startup the volume is set relatively low (2), and then cranked up really slowly, the distortion does not occur and the sound stays good (until it goes 4 +, but I never put it that loud).

I tried the test with headphones: can't hear the distortion in them, but it's really hard to tell even with the speaker turned against a wall...

My present assumption is that maybe an output transistor is failing: When I first acquired the beomaster, last year, it was sold with the "right side too hot" problem. Maybe some of them badly aged, giving me the current problem... A big job that i'm not ready to tackle yet...

hamacbleu
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Hi to all...

Back with my distortion problem which has been unresolved since the past 4 month... In the last month I reopened the machine two times and found out some strange behaviours. I'd like to have an opinion on that:

- A few weeks ago, after a first check-up, the clipping light shows out for the first time. So the distortion is a clipping problem...

-Probably a crossover distortion problem: the idle current adjustment is set to about 4mV Surprise.

However, turning the pot clockwise does not change a lot: I could go all the way up and it would barely go to 6 mV. (I'm avoiding doing that, I know how it is supposed to respond when operating properly, and I know the relative position of the pot when it's set to 18mV. I let it this way to avoid any fireworks. (pointing at about 35-40 minutes...)

Assuming that the pot is brand new, that all the caps have been changed and that the emmitter resistors still shows a good value, what can be the cause of this too low voltage between them when idled?

-The offset is set dead down to 0V

-The distortion occurs sooner or later depending on the level of the input

-The distortion does not occur using headphones and turning off the speakers switch.

-I've reflowed the solder joints, especially under TR207 and TR2011 which showed some cracks...

Thanks to all for your input... 

Guillaume

hamacbleu
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SOLVED!

... I know it's been almost a year. It's just that I didn't wanted to change the TIPS by myself because of a lack of experience.

The TIPS were the problem indeed. It was not surprising: when I acquired that machine 2 years ago, I could have cook an egg on the right sink... 

All 6 were changed. 

Both amplifiers are now like new...

The combination with the Beogram 8000 is something really powerful: practically no noises during silences and then Bang! when a piece starts it hits you in the face... I'm no audiophile at all, but there's definitely something here...

Having used my Beomaster 2400 since a whole year as a substitute, I'm still amazed when I get back to this mammoth. Though I must admit that the 2400 is really decent, beautiful and reliable...

On a side note: it's strange how some audiophile salesman denigrates B&O here in Quebec... I've been told that the "pivot" on the Beogram 8000 was crap... what was that about??

It reminds me of the useless war between Mac and PC's... If both things exists, that's probably because they both answer a particular need?... Same goes for B&O..

Anyways...

Guillaume

sonavor
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Congratulations Guillaume. I'm glad to hear you are enjoying a functioning 8000 system again. I agree with you that it is a great system...and under rated by a lot of people. -sonavor
Søren Mexico
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hamacbleu:
Having used my Beomaster 2400 since a whole year as a substitute, I'm still amazed when I get back to this mammoth. Though I must admit that the 2400 is really decent, beautiful and reliable...

Compliments Guillaume, to find the failures and solve the problems, brings more joy to the listening, I have a BG 2404 and I must say it comes very near to my BG 5000 (pizza box) and as you say about your 2400, always reliable and a very good TT. At the moment I am testing MMCs, MMC2 and MMC4s from Axel, I never thought that the difference between MMC2 and 4 would be that big, now I wonder why I ordered 2 pcs. MMC4 and 1 pcs. MMC2, and not 3 pcs, MMC2

Collecting Vintage B&O is not a hobby, its a lifestyle.

chartz
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chartz replied on Fri, Jun 20 2014 10:07 AM

hamacbleu:

On a side note: it's strange how some audiophile salesman denigrates B&O here in Quebec... I've been told that the "pivot" on the Beogram 8000 was crap... what was that about??

It reminds me of the useless war between Mac and PC's... If both things exists, that's probably because they both answer a particular need?... Same goes for B&O..

Anyways...

The pivot is perfectly fine, and just don't listen to those nay-say audiofools and incompetent retailers, listen to your equipment and enjoy it!

Smile

 

Jacques

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