MFB 545 - Bass driver oscillatie

[markkelsall]

Unless you know of someone who wants to sell a pair of 545's??

[Thomas]

I would be happy to adopt the faulty pair and sell a perfectly serviced pair instead

[markkelsall]

HI Thomas

Thanks for the offer but I think he'll want too much for them, although Denmark is a bit closer to you than to me!

How much would you want for your 545's?

Mark

[Thomas]

Hi Mark,

Denmark, hmm, could be interesting.

I'll send you a PB about the 545's!

[markkelsall]

And here is a link to a Youtube video clip of the bass oscillation

Thoughts please

Note also the LED's. Only two lit

https://youtu.be/5-sVpiFLyfE

[rob040]

I can't play the video, since it is a private one...

[markkelsall]

My mistake. Try again!

https://youtu.be/5-sVpiFLyfE

[Thomas]

That looks a lot like the MFB sensor is generatief faulty feedback, possibly a bad BFW11 fet inside the woofer. I say possibly, there could be more causes for this problem.

About the LED's, in the video the automatic led is not working, this is a setting of the top right input dial knob. It is set to asymmetrical input and always-on situation, thus bypassing the automatic power-on circuit.

[markkelsall]

Thanks Thomas

I have sent you a PM.

Mark

[David]

I don't think it's a bass driver oscillation. It looks like an acceleration sensor issue.

There is an easy way to verify this: by disconnecting the feedback signal. The easiest way to do this is by woofer dis-assembly and then take the feedback wire off (desolder 1 signal lead).

If, when powered on, the woofer stays stable, most likely the sensor is faulty.

It could also be the input circuit on the 545 but that is less likely.

A woofer swap would be more conclusive but also more work, and after finding where the problem lies, you would need to swap the woofers back as the alignment is woofer dependant.