Hi!

I have a Beomaster 4500 hooked up to my Beovision MX 6000. Beomaster 4500 has two left and two right audio channels. The first left channel is dead, I think i might have shortcut it by mistake long ago. However the second left channel works perfectly fine but I would like to be able to use the first channels since I want to use my MCL on the second channel. Also, the mute function only mutes the first channels, so I need them to be working. I have opened the Beomaster and i find no fuses to the audio channels.

So my question is: How do i fix this and is there a fuse I might have blown? I am pretty good at soldering so I might be able to fix this, I just don´t know where to look.

There are no fuses to blow in the outputs.

You have already pretty much diagnosed that you need a new muting relay (the one that clicks when you operate mute). The 1st speaker outputs are routed through it. Don't bother trying to clean it unless you want to do that regularly in the future, that fix will never last long. This is a common problem with all Beomasters and Beoenters from that era.

I haven't been inside a BM4500 myself, but you might find a more specific description if you search the forums. New relays are probably available from B&O, but if you can find a generic replacement it will be cheaper.

Of course check first that the problem isn't simply in the output socket or its wiring.

Thanks a lot for the help! I took some time taking pictures inside my Beomaster 4500, and I found the "clicking" muting relay, wich is marked "speker relay" on the motherboard. I marked this one on the third picture. Over to the pictures:

Is it just to go to a local Bang & Olufsen shop and ask them if they can order a speaker relay to Beomaster 4500?

mattiasf92:

Is it just to go to a local Bang & Olufsen shop and ask them if they can order a speaker relay to Beomaster 4500?

Basically yes - according to the service manual the part number for it is 7600093, which might also be helpful

However, not all dealers are willing to order & sell spare parts to end users, and I'm not 100% sure it is even available. Never hurts to ask!

The relay has a 9V coil and I'm sure it's a regular off-the-shelf type from some manufacturer, but it may be a bit of work trying to source one elsewhere.

You could of course try to open it and clean the contact points just to make sure that the fault is in the relay (I'm just trying to cover my back here so that you can't blame me for having to buy an unnecessary spare part ). Don't use sand paper or any all-purpose sprays; dip a piece of regular printer paper in isopropanol and just pull it between the contacts. It should remove some oxidation and the relay should work at least for a while.

Why will it help if i clean it, and is it the contact points under the motherboard i shall clean?

Edit: or is it inside the relay?

mattiasf92:

Why will it help if i clean it, and is it the contact points under the motherboard i shall clean?

No. You need to remove the relay, open it (the clear plastic case comes off some way or another) and clean the contacts inside it!

Okay, thanks. I´ll try that. I´m pretty sure i shortcut the + and - poles on the first left channel by mistake, so that might have blown the relay. The second left works, so i cannot have blown the entire channel, right?

I don't think the shortcut is to blame. You're right there's only one amplifier output per channel - if anything electronic had been fried, you wouldn't have sound from the L2 output either.

There's not much else than can be at fault except the relay, the speaker socket, or wiring between them. You should check the solderings of the socket as well.

I opened up the plastics and cleaned it.

It looks like there´s a electro magnet that controls the switch, it´s really simple. But when i put it together the magnet doesn´t seems to work anymore and I don´t hear the clicking sound... But if i pushes it manually, without the plastic case i get sound in both speakers on channel 1, so thanks a lot for the help with that!

EDIT: I fixed the control switch, it was a soldering under the motherboard that must have broken when i removed the plastic case. So now both channels and the muting relay works fine! Thanks again!

mattiasf92:

EDIT: I fixed the control switch, it was a soldering under the motherboard that must have broken when i removed the plastic case. So now both channels and the muting relay works fine! Thanks again!

Very good

With a bit of luck, it will work for a good while without problems. But the next time the no. 1 speaker outputs start acting up, you'll probably need to get the new relay. But now you know where to begin