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BeoLab 4000 - Does not turn on - Diode is RED

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Ravsted
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Ravsted posted on Tue, Jan 14 2020 10:36 AM

Hi

I've bought a pair of BL4000 and a BS2300. I knew there were issues with it and I do know about the famous sticky black foam in the Beolabs.

But no risk - no fun.

I took both speakers apart. Cleaned the amp, put new foam in. Success with one speaker ... But not with the other.

It stays in stand by. Does not power on neither via PL or RCA.

I have a multimeter but I am not very qualified in using it and I read a lot of posts in this forum but have not found a step-step guide.

A bit of help would be appreciated.

Would like to bring this beautiful speaker back to life...

 

Regards 

Ravsted

 

 

 

 

 

 

 

 

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ProGram
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ProGram replied on Tue, Jan 14 2020 11:20 AM
Look for broken traces and parts, mostly resistors. Perhaps around P4 on the bigger pcb. It looks not so good on your photo
Ravsted
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Ravsted replied on Tue, Jan 14 2020 11:38 AM

Close up picture of area around P4

Assume P4 + ribbon cable is triggering the relay ? If so... can I bypass that just to check if the amp is working then ?

Ravsted
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Ravsted replied on Tue, Jan 14 2020 12:41 PM

I measure 28V between pin 1 and pin 2 on P4.

According to service manual it should be 23,5 in standby.

 

Fuses F1, F2 and F5 on PCB1 (PowerSupply Board) are fine.

I have also checked TR91, TR92 and TR93 on the Amplifier Board. I get a reading on all 3.

 

What would be the next thing to measure and how do I measure ?

ProGram
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The corrosion was my first idea. Of course there might be an electrical fault as well. But I have no manual right now.
Ravsted
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Manual:

http://www.ravstedlokalhistorie.dk/share/document.pdf

 

Ravsted
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Maybe I am getting closer to a reason

Resistor TR91 and TR120 should be NPN type BC847B

I have correct reading on TR91

But TR120 gives me a reading both ways between Base and Emitter. Guess that is wrong.

Service manual says: Check that 2TR120, 121 and 122 are all pulled on. But what does that mean ? Pulled on ?

ProGram
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I think they mean that they are switching the 23v to ground (over the relay), what activates the relay. (Tr122)
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