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Beolab 4000 red led no Green led

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chti59
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chti59 posted on Sat, Feb 16 2019 11:43 AM

Hi everyone

Just got in a nice pair of black beolab 4000. I plugged them into my beosound ouverture.

They just stay stuck on red led and never goes to green. What is strange is that they both have the same fault. Checked the forum but only found transformer problems.

Until now

Tested F5 = OK
Tested T1 = 23V
RL1 between 4 and 5 = no voltage to the coil (which was expected)

Wanted to test TR1 but it is behind a plastic holder, so before going further.

so it's in between somewhere If anyone had this problem and knows what to check first.

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chti59
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chti59 replied on Tue, Jun 15 2021 1:30 PM

Hi Manfy

I do not have a replacement, this night I pulled out the treble and open it, the 2 wires were not connected to their little pole, how can that happen I do not know. I have Tried to solder the wire back on their place but the solder is not staying on it, it is running aways and the wire were too short.

Then I have opened the tweeter just to see if inside there is still a continuity to the wire and yes the wire is OK but was too short and impossible to solder.

I will effectively put a new one and as you say put the adjustable resistor in the middle position.

Here is the pictures of mine opened.

 

manfy
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manfy replied on Tue, Jun 15 2021 2:03 PM

Interesting!

I'd say it's unlikely that the voice coil wire broke because of overload. If so, that would have happened somewhere within the coil.
Probably the previous owner was "playing around" and accidentally broke those wires.

Yes, you cannot easily solder them. Similar to transformer wire it is lacquer coated and it can withstand temperatures up to 200+ Celsius.
On thick wire the lacqer needs to be scratched off for soldering, but don't do that here! It could damage the voice coil beyond repair.
Set your soldering iron to max. temperature (which is usually around 400C) and carefully "burn off" that insulation at the last 5mm where you want ot solder the connecting wire. Once that's done, you can solder it easily to a copper strand for connection to the terminal.

Do NOT readjust the amp setting yet if you are using the very same speaker! If it is the original driver, you can assume that the setting is correct.
Fix the wires and test the speaker. If it sounds good (and balanced with the other channel) leave the amplifier setting as is!

---------------------------

PS: An afterthought: You could also use a normal cigarette lighter to burn off the insulation at the end of the voice coil wire! The Butane flame surely burns beyond 1000C and that will definitely burn off any lacquer coating...and it is non-contact, i.e. no danger to the wire because of mechanical forces!

chti59
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chti59 replied on Wed, Jun 16 2021 9:06 AM

Hi

Just checked and the other speaker tweeter is also dead, so certainly to much volume.

Which glue are you guys unsing to reglue the dome of the tweter.?

manfy
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manfy replied on Wed, Jun 16 2021 11:39 AM

chti59:

Hi

Just checked and the other speaker tweeter is also dead, so certainly to much volume.

Hmmmm, I think you're jumping to conclusions -- in this case a potentially wrong one!

It can't be an excursion fault because tweeter coils don't travel that far. It can't be overheating because you would see a fried voice coil or at least signs of overheating. The connecting wire definitely wouldn't fail of overheating -- mechanical stress and aging of the wire maybe, but certainly not overheating.

Additionally, I see in diagram B that the Beo designers added a 'treble protect' circuit to the amplifier. If I read the diagram correctly, it shorts the input to GND if there is an excessive output voltage. That means the tweeter is basically overload protected.

Now I'd actually be more worried that something might be wrong with the amplifier chip or this overload protection circuit.
I guess it's time to measure the output voltage as per service manual: connect a signal generator with a 10kHz, 100mVrms signal and check what you get at the tweeter output. If you measure the input pin1 of the STK4152, you can assess the load level of the chip and the speaker. The STK4152 datasheet shows that an input of 100mV is roughly equivalent to 10W at 40dB gain; 200mV is above 40W, ie. actually beyond the spec'd 30W max output.

If you don't want to check that, you're running the risk of damaging new tweeters quite quickly!

 

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