Sign in   |  Join   |  Help
Click here to tell us about your new email address

Beolab 4000 power fault

rated by 0 users
Not Answered This post has 0 verified answers | 16 Replies | 1 Follower

BenSA
Top 75 Contributor
Durban, South Africa
1,059 Posts
OFFLINE
Bronze Member
BenSA posted on Sat, Jun 24 2017 11:23 AM

Hi

One of my Beolab 4000 MK2 speakers has developed a problem. it keeps blowing a cap on the amp board. With the help of a friend we managed to trace the issue to the power supply board. There is no -12V output on pins 4 and 5. it seems impossible to trace which component is at fault. Anyone have any ideas or does someone have a board to sell me?

 

Thanks

Ben

All Replies

Søren Mexico
Top 10 Contributor
Mexico City
5,934 Posts
OFFLINE
Bronze Member

Check the standby transformer

Collecting Vintage B&O is not a hobby, its a lifestyle.

BenSA
Top 75 Contributor
Durban, South Africa
1,059 Posts
OFFLINE
Bronze Member
BenSA replied on Sat, Jun 24 2017 6:33 PM

Hi Soren

Thank you for replying. We checked the standby and it measures 12V so surely it can't be the transformer?

The speaker powers up but after a few seconds the cap blows. It just seems impossible without a circuit diagram to be able to trace which part could be faulty. I have the service manual but they just recommend to change a module when there is an issue. Is changing the module the only option?

Dillen
Top 10 Contributor
Copenhagen / Denmark
9,420 Posts
OFFLINE
Founder
Moderator
Dillen replied on Sat, Jun 24 2017 6:48 PM

Which cap?
Photo? 

Martin

BenSA
Top 75 Contributor
Durban, South Africa
1,059 Posts
OFFLINE
Bronze Member

Hi Martin

i was hoping you'd read my thread :)

I have attached a photo of the amp board where the cap blows on the -12V input line. its the one with the arrow pointing to it. These are the original caps that were fitted to the speaker. We then changed those 2 caps as the originals were swollen. On powering up again we had only the one cap blow.

As previously said we found that there is no -12V output from the power supply board. The +12V line and the +12V standby line are fine. -12V pin 4 and  pin 5 are reading zero Volts. Any ideas?

Thanks

Ben


Dillen
Top 10 Contributor
Copenhagen / Denmark
9,420 Posts
OFFLINE
Founder
Moderator
Dillen replied on Sat, Jun 24 2017 9:26 PM

Check copper traces on the board(s) where foam has been in contact.
It's quite common to find that it has eaten away at the copper. 

Martin

BenSA
Top 75 Contributor
Durban, South Africa
1,059 Posts
OFFLINE
Bronze Member
BenSA replied on Sun, Jun 25 2017 9:23 AM

Hi Martin

We've checked the boards, cleaned them, no corrosion from the foam at all. Any other ideas or tips?

Thanks

Ben

solderon29
Top 200 Contributor
U.K.West Midlands
276 Posts
OFFLINE
Gold Member

These Mk2 Beolab 4000's employ the B&O Icepower amplifier modules.Although tiny,they are quite complex and not really designed or indeed practical to repair.

It's quite common for the tweeter to fail short circuit,and it might be worth checking this,but otherwise I think you will have to be resigned to replacing the module?

I wonder about the debris on the board shown in your photo?

The Mk2 version doesn't usually suffer from the common "evil foam residue"issue as B&O of course stopped using the old black stuff with this and contemporary models.

Regards,

Nick

marc
Top 500 Contributor
netherlands
55 Posts
OFFLINE
Bronze Member
marc replied on Sun, Jun 25 2017 10:45 AM

maybe a stupid question, is the polarity of the cap correct?

BenSA
Top 75 Contributor
Durban, South Africa
1,059 Posts
OFFLINE
Bronze Member
BenSA replied on Sun, Jun 25 2017 5:49 PM

Hi

Polarity of the cap is correct, I double checked again. (Any check is worth mentioning)

We did some more checking and now understand the circuitry a bit more and this is what we have found:

1. The -12V line switches on correctly when a signal is applied to the speaker. 

2. The +12V line is on all the time, regardless if a signal is applied or not. We have checked on the other working Beolab and this line should be off       when no signal is applied. 

3. With no amp board connected that status LED switches from Red to Green when a signal is applied to the speaker.

4. With the amp board connected the status LED pulsates rapidly.

Any thoughts on this findings?

Thanks again

Ben

marc
Top 500 Contributor
netherlands
55 Posts
OFFLINE
Bronze Member
marc replied on Sun, Jun 25 2017 5:51 PM

i would say that the amp board has a short or something, i would start measuring there.

Good luck!

marexy
Top 200 Contributor
286 Posts
OFFLINE
Bronze Member
marexy replied on Mon, Jun 26 2017 12:48 PM

these digital amps....no go...

BL4000 clasic trafo amplifiers MK1  are4ever :)

Sorry ..i have same problems with BL4.

 

 

BenSA
Top 75 Contributor
Durban, South Africa
1,059 Posts
OFFLINE
Bronze Member
BenSA replied on Mon, Jun 26 2017 12:53 PM

marexy:

these digital amps....no go...

BL4000 clasic trafo amplifiers MK1  are4ever :)

Sorry ..i have same problems with BL4.

 

 

So clearly its better to have the MK1 speakers! Such a pity as they are impressive the MK2. I have asked for a quote for new boards from B&O but I suspect the price will be astronomical....otherwise I must look out for one lonely BL4000 speaker.

Thanks everyone for the help though.

.Ben

BenSA
Top 75 Contributor
Durban, South Africa
1,059 Posts
OFFLINE
Bronze Member
BenSA replied on Mon, Jun 26 2017 1:41 PM

Just for everyone's information, the cost of the power board and amp board is around 133 pounds. That's not bad. I am ordering one of each.

solderon29
Top 200 Contributor
U.K.West Midlands
276 Posts
OFFLINE
Gold Member

Thanks for sharing info,that costing makes the repair "do-able",although I imagine when you factor in labour costs,it  could be at least double that if the work were done by a B&O service agent ?

Check the tweeter before fitting and powering up the new modules?

Regards,

Nick

Page 1 of 2 (17 items) 1 2 Next > | RSS