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 

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.

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. 

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.

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...

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.

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)

 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.

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.