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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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nanan
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nanan replied on Sun, Feb 17 2019 2:41 PM

You should check R139, R126 and R192 resistor anf the continuity near P4 and P7 on one board and R138, R127, R137 (R95, R96, R94 too) on the other board. 

Let us know what is the outcome.

 

Regards 

chti59
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chti59 replied on Mon, Feb 18 2019 11:17 AM

Hi Nanan

Thank you for your suggestion, but after looking on the PCB after the mentioned component on your post, I found out that someone before tried to fix it, 

R138,R127,R137, TR127, TR128 are not even there anymore. Dozens of components have been unsoldered and resoldered but really not to industry standarts, very ugly soldering technique, looks like they did not have the micro-soldering tools needed for such repairs.

Then I opened the second one and it is even worth, cutted cables, wire bridges, dozens resoldered components etc....

I think that some people should better do plumbing and leave B&O materials for the others.

It's a shame but unless changing both input and crossover PCB's it will use too much time to fix them.

nanan
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nanan replied on Sat, Feb 23 2019 2:32 PM

Hi, I see. What a shame. 

 

I see you live in France, I'm myself living in Switzerland and I'm experienced with repairing various Bang & Olufsen products (BeoLab 4000 is a commun one). Maybe I can help you with the boards. 

 

Don't hesitate to contact me if needed. 

chti59
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chti59 replied on Wed, Feb 27 2019 10:33 AM

Hi Nanan

Yes it's a shame

I will post some pictures when I will get back on it, certainly during the summer, that is when I get some time to work on such time consuming items. Will let you know by PM also.

It is even worth showing what some people are able to do on such nice speakers, and really what not to do on such nice speakers.

Yesterday I worked on a beolab 2500 green led no sound and once open I took out the PCB and connected it back to the speaker with PCB flat on the bench, once connected it started to work ???

No dry solder found. So I suppose that it was somewhere a contact or connector problem but where ??? will have to spray some contact cleaner on all connectors and hope for the best.

 

chti59
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chti59 replied on Thu, Jun 10 2021 6:52 PM

Hi everyone

I am back on these speaker and I am exchanging components from one board to another to fix the one not working.I know it's a long time that they lay around, but life sometimes.....

When I check R126 on the service manual I cannot find it and the PDF is not searchable, I suppose because it is a scan and not made with acrobat writer or else.

Would this mean that I have to trust the value writen on the component ? or do I miss something ?

Could someone explain the numbers around the schematics like B3 or B4 or A8 A9 where do they connect ?
Does it mean that A3 connects to B3 etc...

chti59
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chti59 replied on Fri, Jun 11 2021 3:09 PM

Ok found a reply most of my questions.

Now :

R139 has 29V send to TR122

TR122 : I Have 29V volts on the collector but then ??????

I have changed twice the TR122 to be shure but only 29V on the collector

Tested R95 R96 R94 and R127 R137 R138 and R126 R139 R192 all seem fine, I must not understand something.

 

Any help will be appreciated.

manfy
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manfy replied on Fri, Jun 11 2021 6:40 PM

You have to look at all the circuitry that can activate/deactivate the relay to be able to pinpoint the source of the problem!

Let's start with the most obvious ones:
With the Beolab in standby, connected via powerlink to your Beo amplifier and this unit powered up and running, measure the voltages at following points with reference to GND.

1) emitter of TR93
2) emitter of TR91
3) DC FAIL signal (as seen on bottom left corner of diagramm A) = input side of R92
4) 'speaker on' signal at pin 4 of powerlink socket (= input side of R120)

 

chti59
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chti59 replied on Sun, Jun 13 2021 2:04 AM

 Hi 

Testing R120 showed me a problem the resistance showed E22 and that is a 7.5 MΩ resistor so I replaced with the correct value.

One thing is shure it is that the guy that fooled around before me did a big mess and it is not the first replacement there was also a resistor with 180 ohms and it should have been a 100 ohms, meaning that the guy did not had a microscope.

Anyway

R120 = 4.55V
TR93 = nothing
TR91 = nothing
R92 = nothing

it is 3.h05 AM and I quit for tonight will keep the search tomorrow night as I suppose I have to trace DC fails on diagram B.

manfy
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manfy replied on Sun, Jun 13 2021 7:12 AM

Thanks!

- 'speaker on' signal from power link: 4.5V is good!
The power link specs say: ON-signal should be >=2.5V, OFF-signal <=0.5V

- 'DC Fail' signal at 0V: good!
The signal gives the difference between the two speaker outputs. Normally this should be 0V. If the DC-offset goes beyond approx +/-2V, the DC-Protection circuit (TR91/92/93) will switch the relay off and you cannot on the speaker unless you cycle the power.

- emitter of TR93 at 0V: NOT GOOD!
At standby you should read +23V (or whatever the +23Vstdby voltage at the rectifier D1, PCB1 is) and when the relay switches on, the emitter will drop a bit. I can imagine following reasons for this fault:

a) somehow the standby voltage gets lost between rectifier and DC-Protect circuit, e.g. connector or wiring problem, damaged PCB track, etc.
b) something is causing a short circuit to GND in this DC-protect or relay-control circuit; e.g. sloopy soldering work, shorted transistor, etc.

Power down and disconnect the Beolab. In resistance mode or continuity mode check emiiter of TR93 to GND and other points that are marked with +23V STBY in diagram A. If you measure small resistance in any of thise points, investigate.
But if all those measurements are good, measure continuity from +23V STBY directly at the rectifier D1 to every point that reads +23V STBY in diagram A. If any of those points read more yhan 0-5ohm then investigate.

As soon as you managed to restore 23V at emitter of TR93, we can continue to troubleshoot other problems.

Beobuddy
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Beobuddy replied on Sun, Jun 13 2021 12:25 PM

Depending on which version (left or right) doesn’t work, you should check the traces on the boards. 
Components are affected. Before replacing them you should clean the surface with a fiberglass stick. You will find several broken traces which you won’t see with your eyes when are still covered by pieces of old foam. 
Even around some testpoints there are possible broken traces to be found. All can cause the above described symptoms. 
Start at the places where you found the foam sticked at the board.  

chti59
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chti59 replied on Sun, Jun 13 2021 6:58 PM

Hi Beobuddy

Thank you, it all has been cleaned and traces were repaired under a microscope and tested (my eyes are too old to work without it, and as I also repair cellular phones it is not possible to solder without a microscope. Most repairs are iphones and it is always the same problems, like you guys know better than me with B&O, that is why I ask here ;)

But dit not check around testing point good idea will check tonight.

chti59
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chti59 replied on Mon, Jun 14 2021 7:05 PM

Hi everyone.

I had already replaced R96 but taking voltage again found 29 volts but nothing on the other side.

Could it be that a wrong value ont the parts around it that had the wrong value could have blow the resistor ???

Who knows !!!! anyway it's finaly working, now I just have to order new parts like resistor, transistor, caps etc that I pulled out of a working unit

I alsays use the parts of a working unit because exchanging from one place to another same place is very easy and you know it is working.

Thanks to all for the help and yes that FOAM ROT is a plague that makes us works hours to clean and rebuild the traces, for me this is a problem that was there the day that they have been purchased so B&O should have been responsable for it and recall or sending new foam free at least.

I have a 2008 chrysler grand voyager and the emblem on the stering wheel is hurting when the airbag deploys in an accident.

Well chrysler sent me a letter that they are recalling all the cars even that I am not the first original owner of the car. But today they have acces to our address through our VIN number.

Keep this forum repair up and working as this is good for the earth and saving our kids future house.

chti59
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chti59 replied on Mon, Jun 14 2021 8:57 PM

OUPS... Talked a little too fast, the top speaker is not working but I should managed... The tweeter is dead.

When you change tweter or boomer there is a procedure in the service manual to adjust like the number on the back of the speaker.

Their is plenty of number on the back, which number ?

manfy
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manfy replied on Tue, Jun 15 2021 8:17 AM

Congratz on your successful fix of the original problem!

chti59:
.

Their is plenty of number on the back, which number ?

I just googled the net and it seems that some replacement tweeters do show the db-level on their label while others do not. Here's one example with -0.2dB:

If you don't have that, you're out of luck. All you can do is to assume that it has a flat frequency response and adjust 2R51 as if the chassis were 0.0dB.

Alternatively you could measure the actual frequency response of the speakers, but that needs a measuring mike and some high quality - thus high price - equipment and that's probably not worth it.

Are both tweeters without dB-value, I mean the damaged one and the replacement tweeter? Even the full range speakers? If so, maybe B&O dropped the concept of measuring and adjusting the response due to cost reasons!? Who knows...!
In this case it's probably best to set the amplifier to middle position, i.e. 0.0dB.

 

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