You go in through the woofer hole and/or remove the screws at the back.
/forum/imported-unmapped/m75crossover-diagram#post-2198144

Martin

Thank you Martin.

Oddly enough, this is what I already did, BUT I was afraid to push hard enough on the back panel. Even tried a rubber hammer.

I need to remove the woofers and mid-ranges for re-foaming anyway, but now I know how to get in an investigate.

Now I gotta hope that the fault is obvious enough for a layperson to recognize.

Could it possibly have anything to do with the over-ride protection? Had that issue with my MC120.2 speakers and had to bypass the protection circuit as switch are not available. (You might remember all that....)

Jeff

Opened up the M75 and this is what I found.

I checked the outlet for corrosion but the outlet was pristine. No broken wires, and the caps all look good. I swapped speaker cables just in case, but not the cable.

There is NO sound of any kind, so is there anything else to do other than send the board off for proper testing?

Jeff

Second photo.

This is photo 3.

Last but NOT least, photo 4.

Piaf wrote:

There is NO sound of any kind, so is there anything else to do other than send the board off for proper testing?

Check the safety circuit relay etc.

Martin

Hello Martin,

At some point all this intense "hand holding" must be annoying to any B&O maven.Sorry about that.

But as I have no choice but to look stupid (again), where is the safety circuit  and how do I test it?

Jeff

Hi Jeff,

Here is the schematic of your M75. It shows the relay (RL1) Martin is referring to. You should be able to physically trace wiring from the speaker DIN jack to the relay.