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Beolab 4 repair , fix it, bin it,It's worth it ??

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marexy posted on Tue, Sep 3 2019 7:19 PM

but what  IF ..




First of all, I welcome all forums members and users of that  and ozhers B&O products.
Like many of you, I purchase quite a few units during years and after some time some of them needs attention. some more some less..
But most of all, I want to bring to life the Beolab4 speakers.

As my darling wife like to listen to them in office :)

Why 4 broken pcs. Ok…2 of them I purchase from collegue and they work for 2 years then die…ende, vege, game over

And than I purchase oline 2 in perfect condition…yap…you wish…one work for one month and the other for 3 month..


And the reason of course....taaadaaaa





The amplifier board is defective in all of them.
This is also the reason for 95% (or meore) off all errors on these speakers.

Let me highlight the purpose of this post.
Simply, an astronomical price for a spare part that is over € 100 a piece.
With an official B&O service shop 130€ + labor which I find shameful for such a small piece of electronics PCB board.
A friendly user and a true expert on these forum offered me a reasonable price, but it is still too high and un- economical for me.
Let me clarify.

It is not economical to repair on component basis, for customers, because it is too time-consuming and you can not give as much warranty as for new one plus you can not firnd original MOSFET ST9F3LL any more.

In addition, you can actually buy a pair of used working speakers for around € 150. to 250€ .so the same price as spare PCB amplifier borad.

So the repair is not theoretically and economically worth if you not do it for your selfe.
But since electronics is one of my hobbies and relaxing my nerves after a busy day at the company, it will be a bit of a challenge for me to have a little education and a joy to repair. In this modern world where repair is already economically unacceptable, I find all this sad.
Everybody throws away things that can actually be fixed ( ok..some more some less )
I will write this post in stages as I find the time, the moment of inspiration, and the spare parts.
I also hope for your help if you have any broken PCB’s to donate for my experimentation :)

You can find 2 photos of that PCB.

on fist photo you find  some sound processors and on the other MOS transitors that are usuly faulty.

also 10 ohm resistor is damaged and some transistors in the area.

I did fix some of that power boards to my friands but i can not be 100% that they work for long time.












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MCB replied on Tue, Oct 8 2019 7:45 PM

B&O has switched from STS9NF3LL to FDS6294 in later production of the pcb

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marexy replied on Wed, Oct 9 2019 10:21 AM


Try to change only bad one but is better to change all 4 on the same side.


Hemenex ..thanks

Yes it is correct datasheet.

If you check item TS7NF60L it is not so differnt but it is not ok heating badley fast.

If you put finger on ti when speaker is working  and it is can feel it, so from my point of wiew it's not safe to use it.

There are some WWW pager that offer "" original" parts ..but i tihk all are fake.






Top 150 Contributor
521 Posts
Silver Member
marexy replied on Wed, Oct 9 2019 10:36 AM

""Also, should I replace all ST9F3LL mosfets, or once the defective one is found I can leave the others in place? Are they failing because they don't age well or because they are used near their limits? ""


Yes ..maybe they are used near their limits..can't say without shematics and correct service manual.

Or just generaly poor design of PCB from start.

plus i'm not el.rapir geek to be smart and i can give only my point of perspective.

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