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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
Check the standby transformer
Collecting Vintage B&O is not a hobby, its a lifestyle.
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?
Which cap?Photo?
Martin
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?
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.
We've checked the boards, cleaned them, no corrosion from the foam at all. Any other ideas or tips?
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
maybe a stupid question, is the polarity of the cap correct?
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
i would say that the amp board has a short or something, i would start measuring there.
Good luck!
these digital amps....no go...
BL4000 clasic trafo amplifiers MK1 are4ever :)
Sorry ..i have same problems with BL4.
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
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.
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?
solderon29: 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
Thanks Nick, my friend who was helping me with the repair said he checked but I will make sure we check the tweeter again. I expected the cost for two modules to be a lot more so it was a pleasant surprise. Also i really like the speakers so its worth it for me and also I am able to fit the modules myself which I am sure brings down the cost substantially. A friend will bring them to South Africa from the UK on the 14th July so not too long to wait.
Just an update concerning my Beolab 4000. Although mine are the Mk2 and doesn't have the black foam....it does have the black foam wrapped around the wiring. You wouldn't think that it would cause a problem as there isn't much of that foam but on checking under a magnifying glass, the foam has disintegrated partially leaving gunk around the components. I would suggest that anyone with a MK2 should open and clean their 4000's and replace the black foam with a more suitable foam. This is what definitely caused my speaker to fail.