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Beolab 4000 questions - foam rot

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h1npw
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h1npw posted on Sun, Mar 5 2017 2:06 PM

I'm looking to buy a couple of pairs of these great speakers from flea bay... Can anyone tell me 

1) How can you differentiate between those with the black foam inside them that eventually turns to goo, and those with the "stable" white foam, without asking sellers to take their speaker to bits?

2) Did they change the foam when they started production of the Mk2?

3) Did the serial numbers continue in sequence from Mk1 to Mk2?

4) is there a specific serial number point when the foam changed?

Any info will be greatfully received!

Cheers

Nigel

 

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Beobuddy
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StKong:

That would speak for disassembling in situ rather than loving them too much.

I've done several sets for customers who bought them and came home and then had the surprise of a non-working speaker. They had seen them in working order.

 

Beobuddy
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marexy:

You can use fome simelar to what is inside. do not buy original ..to expencive.

The costs (few euros) are negligible to the actual trade value. So, why not using original proper fitting foam?

 

marexy
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marexy replied on Mon, Mar 6 2017 12:40 PM

Beobuddy

what's your contact mail ?

you can send me p.m.

marexy
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marexy replied on Mon, Mar 6 2017 12:41 PM

sorry ..yes ..how much is original new foam ?

Beobuddy
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marexy:

 

i have repair more than 20 pairs ..and it's no problem.

 

if there is fault on PCB you must check SMD conection on amplifier board on the spots where had beed rotten foam!!

that is all.

 

I have a drawer filled with SMD resistors, capacitors and transistors. All used during several repairs, like with the BL4000.

You can't state that a non-working BL4000 is caused and solved by removing the old foam and some soldering on smd parts.

The tricky thing with the BL4000 is, is that when the BL4000 was assembled at the production-line, the places of the foam differs a little and therefore the location of the culprit. Starting between the difference of a "left" or "right" BL4000.

That makes that even when you have fixed a BL4000, that is it possible after a short period of time  the BL4000 again stops working. Due to traces/joints which are affected by the rotting proces, and finally break. Even when you have cleaned it thoroughly.

A dealer can't afford this and most of the time a complete new amplifierboard is mounted. Which works rock-solid.

That costs you €200,-

 

StKong
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marexy:

Does anyone know if certain factors expedite foam decomposition, such as heat or humidity?

- bad material, not tested enough and after 15 years ...it's like that.. :(

i have repair more than 20 pairs ..and it's no problem.

Take apart spekar

remove, fret, drivers, plastic front, transformator board, remove ALL rotten foam,clean ALL foam left overs on PCB boalrds!!!... with gasolin or isopropanol ( hand desinfective )..

be carefull ...do not spill ..do it wih ear cleaners :)

add new foam...or like..an than put together in reverse order.

spekar not working...than..

if there is fault on PCB you must check SMD conection on amplifier board on the spots where had beed rotten foam!!

that is all.

B&O service will take 200€ for that job...OMG... :(

Thanks, Marexy.

The old forum is full of similar instructions, but the links are usually broken, as in this case: http://archivedforum.beoworld.org/forums/p/41548/344807.aspx

I will give it a go with one speaker and see how it goes. Unsure
StKong
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Beobuddy:

The costs (few euros) are negligible to the actual trade value. So, why not using original proper fitting foam?

Beobuddy, where would one acquire the correct foam?

I remember that someone in a previous thread told me that new foam was unnecessary, bur I am rager to retain my speakers as close to original as possible.
OldJack
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I have a pair of BL4000  for a long time,bought from new,type 6636 , serial no.1644....

Recently I opened one of them for another reason.and found foam to be white,like new.Now,by yours experience,

1) Anybody found foam rot on this (white) foam?

2) Is it recommended to remove and/or replace it ,or i just leave it,as it looks brand new?

 

 

 

 

 

 

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Beobuddy
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Nope, as I already mentioned, this version has fine foam. Just leave it that way.

marexy
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Agree..

some of SMD resistors, capacitors and transistors must be new!

and all the connection where the rottren foam was  must be renew resolder.

In 7 years non of my repaired BL4000 have not stop working.. :)

As you say ..problem are serial no 13,14, and i think some of 15....

Can you tell me the price of white foam for L&R speaker plaese.

Beobuddy..are you official B&O service ?

 I write you mail..did you receive it ?

 

 

Beobuddy
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h1npw
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h1npw replied on Mon, Mar 6 2017 11:06 PM

Wey hey!!!!

We're making progress narrowing down the serial number switch from black to white foam.

if you've got a pair between serial numbers starting 1378 and 1644 can you have a peak inside and let us know the colour of your foam - as previously mentioned, two screws to remove the tweeter and lift it out - you should be able to see the foam.

I'd really like to close the gap!

Cheers

Nigel

marexy
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marexy replied on Tue, Mar 7 2017 12:15 PM

hmm ..hmm...yeah...interesting reaction

Beobuddy
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Don't make it more than it is. There isn't a "gap". Just all BL4000 mk1 prior to serialnumber 15-16 have the same foam.

marexy
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 not written in relation to this topic :)

but ok.. it does not matter..

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