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Beolab 4000 MK1 St-by , ON and OFF switching problem

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marexy
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marexy posted on Tue, Jun 9 2020 10:39 AM

I have a problem repairing Beolab 4000. Super nice speaker, with a common problem of older versions. The speaker works great via the Powerlik connector. The problem is with the RCA connection. The speaker works normally when it receives a signal. The problem occurs when the speaker goes to ST-by after 2 minutes. As soon as it goes to st-by, it turns on again in a few seconds, and turns off in 2 seconds. This rhythm is repeated. I've already looked at all the connections, measured the transistors and resistors, but I can't find any faults.

something on this topic has already been written, and I have tried just about everything, but I have not found a hidden error :(

Thanks

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lawrencejmcook
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marexy:

I have a problem repairing Beolab 4000. Super nice speaker, with a common problem of older versions. The speaker works great via the Powerlik connector. The problem is with the RCA connection. The speaker works normally when it receives a signal. The problem occurs when the speaker goes to ST-by after 2 minutes. As soon as it goes to st-by, it turns on again in a few seconds, and turns off in 2 seconds. This rhythm is repeated. I've already looked at all the connections, measured the transistors and resistors, but I can't find any faults.

something on this topic has already been written, and I have tried just about everything, but I have not found a hidden error :(

Thanks

Hi Marexy,

Is it because the cable is noisy, i.e. is the cable picking up interference and causing the BL4000 to think it is a signal? Does the cable have a “choke” or not?

I had a third-party RJ45 Powerlink to RCA plug cable that picked up a lot of interference, or hum. I replaced it with the official B&O version which had a choke near the RCA ends, and it eliminated the hum.

Lawrence
marexy
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marexy replied on Tue, Jun 9 2020 11:24 AM

Hi

Same cables for both BL 4000 i try...and no problem with other BL 4000.

I also tried different cables, from cheap one  to double shielded. There was the same error :(

 

marexy
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After an hour of checking components no progress :(

found that post : https://forum.recordere.dk/beolab-4000-klikker-on-off_topic155805.html

 

 

Beobuddy
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This one is tricky.

I have spend some time on this and measured with a scope at several points at the same time.

It has to be with the descending voltage across IC1. The plus and minus voltages are not descending equally. That causes at the entrance (!) on pin 3 a burst, which  triggers the autostart circuit. When you lift pin 3 from IC1, then the BL4000 shuts off and doesn't start again.
But that isn't the solution, simply as IC1 is the first IC in line of the complete audiocircuit.

I've changed IC1, but made no difference. The lifted pin 3 still generates that burst.. Trying to help both voltages to descend equally wasn't successful either.

Btw, my BL4000 had no foam issues, like the ones with the black deteriorating foam. 
Will be continued as the others haven't mentioned the solution either. 

marexy
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marexy replied on Wed, Jun 10 2020 12:09 PM
Interestingly, the error is the same as if an IC actually had an error. Maybe there is even a fault somewhere in bad contact or bad smd element or capacitor but this is really looking for a needle in a haystack :(
This speaker had bad foam, but it was all cleaned and all the contacts restored.

I double check all  isk connections on the pcb, but ..no luck :(

 

marexy
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marexy replied on Thu, Jun 11 2020 8:27 AM

Yesterday i replace all SMD transistors plus some resistors.. and no luck..still same error :(

keep you posted..

Beobuddy
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Parts-firing is that called.... Could have told you on forehand that would not work. Unless it's a left version with old foam. Then there have to be replaced several smd parts.
But again, I have a board with the same symptoms, is clean and unaffected by old foam. Serialnumber starts with 18xxx.

Due to more urgent repairs I've replaced to board to minimize the waiting time for the customer. So, it doesn't have my priority at the moment.  

marexy
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marexy replied on Thu, Jun 11 2020 11:28 AM

 

Thanks for answer :)

my BL4000 is serial No 1302.... so old MK1..with rottern foam problem :(

I clean all rotten foam problem an do some additional work as i wrote..but no luck.

so any additional suggeston will help :)

What parts should i repalace in addition to that what i allready done ?

As you are expert, i am sure you did see many of different erroors on these spekers.

It is interesting as weel that both black speakers are not same black colour ..hmm :)

 

 

marexy
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marexy replied on Sat, Aug 15 2020 3:25 PM

After some time i decided to try fixing that BL4000 again.

I check many components and not find any error... :(

Problem is noly when speaker is in position LINE in.

Onposition PWL is all ok.

I think problem is in voltage regulation for automatic ON -OFF.

So any hint..repair trick or magic stick will be welcome :)

 

 

 

leosgonewild
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What is the BL4000’s connected to when this happens?
marexy
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marexy replied on Sun, Aug 16 2020 11:10 AM

Hi 

it is connected via RCA  to peamp or ipod or tv...or nothing at all...it is the same problem

When switch is on position LINE it has a problem.

when on position L ot R on Powerlink it's all ok.

 

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