Old B&O ribbon mic schems...

[Alistair]

I grabbed a Fentone/BM3 B&O ribbon mic off ebay locally a few months ago, and have finally had the time to open it up and try and get it working. The ribbon is torn, which is an obvious fix, but I've also got 3 wires that have snapped off internally. Any ideas where to find a schem or pictures of the internals? The usual sources aren't coming up with much at all. The best I've grabbed is this, which doesn't really show much detail

http://bp3.blogger.com/_fKXlhnDTeys/Rha ... p2%5Bt.jpg (sorry, it won't size up properly and load into the forum)

[Alistair]

Ok... I'm guessing no-one has a clue, but here are some pics of the internals.

You can clearly see the 3 cables that aren't attached, which are black, red and green coloured reading from left to right.

The 3 places with broken cable/solder mess are on the ribbon body- the big blob of solder between the two screws.

On the round disc with yellow thick wire attached- the bottom left dot has a large amount of solder on it.

On the white piece of plastic closest to the metal on the right, there is a grounding tab of some sort. It has remnants of a wire.

So 3 wires, 3 spots...but what where??

Also need to replace the resistor as it's blown out one end.

And yes, I'm well aware it probably needs a ribbon aswell!

EDIT- Sorry, images aren't working. You'll need to follow the links.

http://i17.photobucket.com/albums/b70/alistair016/gibson/boribbon.jpg

http://i17.photobucket.com/albums/b70/alistair016/gibson/bozoom2.jpg

[Futureman]

I don't have much help, except in the past I've gone all CSI and looked real close with a magnifying glass to see if I can recognise which wire was torn from where etc..

I guess you only need to recognise 2 out of the 3 eh?

Good luck...

[Alistair]

Yeah... I tried that. Unfortunately, all the old copper wire has corroded/rusted at the breaks, so all the breaks just have bare wire and green copper rust!

[Kurt]

That's only 9 possible combinations, just hook it up with jumpers 'til it seems to do what it should? I should think it can hurt it.

[Kurt]

Thinking about it some more... SHould one of those 3 wires be a common connected to the body or ribbon motor? That only leaves 2, decide which way is the front of the mic and hook it up so that positive pressure on the front causes positive voltage on whichever pin it's supposed to

That's only 9 possible combinations, just hook it up with jumpers 'til it seems to do what it should? I should think it can hurt it.

[Futureman]

That's only 9 possible combinations, .

Not only 9, It's more like 6

a b c
a c b
b c a
b a c
c a b
c b a

[Kurt]

Dunno, high school maths was an awful long time ago..

[Alistair]

Thinking about it some more... SHould one of those 3 wires be a common connected to the body or ribbon motor?

On the rear of the mic (that you can't see) there is a small red wire running from the transformer onto the ribbon. And I'm pretty sure the dot of solder on the front is a connection as well (I'm guessing positive and negative/ground off the ribbon? I'm not 100% sure how they ribbons work).

Ok- I'll fix the ribbon and then just run the combinations. Thanks guys!