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

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marexy
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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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marexy
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PCB mosfet side


marexy
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Regarding some fault indicator..

If the spekaker is defective and make pulsing sound than you have 30% chance to fix it.

IF the spekar have bad- muffed , distorted sound and bass driver is pushed in or out ..than you have 10% chance for repair.

That is my experiance...maybe  or. .. I am sure ...some forum members have way more success and experience than me.

From my experience , most of the errors are on the woofer part, followed by distortion on both channels, and then error on the tweeter part.

 

 

 

 



 

 

 



 

jvezina
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I own a pair of Beolab 4000 MkII and they have exactly the same amplifier boards. After 10 years, they start to make a loud scratching noise, as if there was a bad contact in them. I have the amplifiers replaced but I kept the defective  boards. I will try to repair them as a hobby and keep them as spares as there is nothing to lose.

Which components have to be checked and eventually replaced? The 10 ohm resistors and the MOSFETs?

There is no schematic so the repair has to be done by trial and error.

Is 9F3LL the official part designation? I checked in the ST Thomson (the manufacturer) web site and I wasn't able to find a MOSFET with similar identification.

Thanks in advance,

Jean

 

marexy
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Interesting story.
A colleague of mine has a friend who take for repair a pair of Beolab 4 speakers to an official B&O repair shop.
Because the cost of repairing and replacing the new parts was too high, he said that he would take the speakers back and sell them as broken.
The next day he came to pick up speakers.

Coincidentally, I met this person few month later and offered that i look at what I could check or fix as a second opinion and as a favor to a friend.
When I opened the unit, I was very surprised.
That's how PCBs look when I take them out of the speakers.
To me, the way that the official B&O repairer returns such plundered parts of the unsuspecting client I find very low.
He probably kept the existing ones for himself, but installed back ones that are total garbage.
A really bad experience and an even worse commercial for this brand and this repair shop.


marexy
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and other side


Dillen
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I wrote about this level of service a.o. some time ago.
Mainly in danish but Google is your friend..
https://forum.beoworld.org/forums/p/7854/69582.aspx#69582

Martin

marexy
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Martin

100% aggree with you.

I's shame that some official B&O repair shop do that kind of dirty practice.

So i try to give my best to fix some boards.

any of your " hint " is welcome :)

 

 

marexy
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ok..let's go on

on these WWW site you can find  interesting data.

https://ham.brugtgrej.dk/forum.php?mode=thread&obj=68196

Did some additionla repair and did fix one board with STS7NF60L mosfet  BUT...it's overheating and FET going to 106 degree in 3 minutes when playing.

for test ..I switched back for the original ones and the overheating is gone.

therefore, are not correct FET components or some elements need to be replaced before the FET transistor.


 

 

 

 


jvezina
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marexy:

ok..let's go on

on these WWW site you can find  interesting data.

https://ham.brugtgrej.dk/forum.php?mode=thread&obj=68196

Did some additionla repair and did fix one board with STS7NF60L mosfet  BUT...it's overheating and FET going to 106 degree in 3 minutes when playing.

for test ..I switched back for the original ones and the overheating is gone.

therefore, are not correct FET components or some elements need to be replaced before the FET transistor.

 

Thanks a lot!

Jean

 

marexy
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marexy replied on Tue, Sep 24 2019 7:20 AM

Now i do have some problems as i have no additional PCB's for more testing and trying to find best way and alternative to fix different errors on that PCB.

So if any of you have faulty, broken, not working or partial working PCB would be happy to buy or if you wish to donate them for ""for scientific purposes""  :)

My shipping costs. 


 

marexy
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If any of you wish to repair it by DIY you need SMD heat gun + smd soldering iron with reguleted temperature.

plus optional accessories such work!

As some of smd component's are 1mmx2mm and on tight space and you can  can easily destroy PCB connections on the board.

 

 

 

 

With some effort I was able to repair one unit and it has been playing successfully for 3 days.

I advise you not to go into repair without at least a basic knowledge of electronics.

One of the  ""professional "" tools .. ha ha


 

 


 

 

 

 

 

 

 

 

 

 


marexy
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marexy replied on Tue, Oct 8 2019 11:05 AM

Hi Jean

Yes...bl4000 Mk2 have the same boards.

There are no PCB Shematics....as i know of...

Maybe some inside B&O info will help...hmmm

In 50% ...maybe 50%... it is ok to change mosfet ST9F3LL but only with the same one as till now i did not find any other option to work and all 4 per clanalle should be changed. And i do not have datasheet for ST9F3LL.

10 ohm change if broken...no need if it is ok.

In many cases there are faults on the top side of board or bad connection inside board.  Note....Repair only with correct smd tools.

any other questtion..PM me

 

jvezina
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marexy:

Hi Jean

Yes...bl4000 Mk2 have the same boards.

There are no PCB Shematics....as i know of...

Maybe some inside B&O info will help...hmmm

In 50% ...maybe 50%... it is ok to change mosfet ST9F3LL but only with the same one as till now i did not find any other option to work and all 4 per clanalle should be changed. And i do not have datasheet for ST9F3LL.

10 ohm change if broken...no need if it is ok.

In many cases there are faults on the top side of board or bad connection inside board.  Note....Repair only with correct smd tools.

any other questtion..PM me

 

Thanks a lot for your very valuable advice!

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?

Regards,

Jean

 

hemenex
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I think the correct FET's devicename is STS9NF3LL

https://www.st.com/resource/en/datasheet/cd00002691.pdf

But they are obsolete... Sad

Regards,

  hx

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