repair help on electrovoice 667a

hey ya'll,

anyone on here have experience repairing electrovoice 667a's?

I just got one on ebay, and like an idiot I unscrewed the two parts of the chassis without first loosening the nut on the back, and as a result put a bunch of strain on the transformer wires contained in there. Two were disconnected from their solder joints. One of them is the heavy red wire that seems to have a clear point of connection on the immediate pcb it meets. That seems relatively simple to get reconnected. My issue is there is a loose, smaller diameter green cable that seems to be part of a transformer configuration (there are 5-6 other colors of similar diameter connected to various terminals). It's supposed to meet one of many vacant terminals on the bottom of the smaller side of the mic chassis that contains the custom EQ pin configuration, but I'm not sure which one is correct. Any tricks for sussing that out? Would it be best to plug the mic in and test what terminal is correct by putting it on different ones and seeing if the mic works? I suppose that would assume everything else is copacetic. But I do know the mic was working before I did the damage.

Secondary question for anyone with specific 667a experience: My instinct was to remove all of the capsule/transformer from the bulky mic housing, so I could potentially troubleshoot anything in there, and make sure to get good access to the pcbs. Is there anything to keep in mind as I attempt this?

Thanks, and sorry for any newbie questions. I have done many DIY building projects and wired my studio but have not done a lot of mic repair.

R

I assume you've already located the engineering spec brochure? There's a wiring diagram there that could be helpful, even though it may not be at the level of detail you're looking for. Attached here.

Have you looked at all the info here:
http://www.coutant.org/667a/

Spec sheet:
http://www.coutant.org/667a/667a.pdf

You should be able to figure out the connections from this info.

But I do know the mic was working before I did the damage.

Click to expand...

My instinct was to remove all of the capsule/transformer from the bulky mic housing, so I could potentially troubleshoot anything in there, and make sure to get good access to the pcbs. Is there anything to keep in mind as I attempt this?

Click to expand...

Why are you taking it apart if it was working???

Buy a broken mic to start learning on. There is definite potential to do damage just taking apart a mic due to the fragile components inside.

P.s. I didn't mean to sound harsh, I've just been in your shoes!
My first instinct is to take everything apart  ;D

dmp said:

P.s. I didn't mean to sound harsh, I've just been in your shoes!
My first instinct is to take everything apart  ;D

Click to expand...

No no, not at all. It was stupid of me. But in my defense, I wasn't trying to take it apart just to take it apart. I thought that twisting the mic apart was the way to get at the nifty EQ selector pins. Turns out I was wrong  Just hoping to salvage the situation. And I guess learn something in the process.

When I mentioned what my "instinct was" I should have used the present tense. At the moment my instinct is to remove the mic parts from the housing to have room to work. Anybody have experience with this being a bad idea, based on the way dynamic mic parts are installed in housing in the factory?

Thanks for the info. There's some helpful stuff there. I really need a schematic to figure out these transformer terminals, since they're not included in the engineers info (as we've established, because they shouldn't be tampered with!), but they probably don't exist. I may have to just use process of elimination. And try not to harm anything in the process.

R

radtunez said:

When I mentioned what my "instinct was" I should have used the present tense. At the moment my instinct is to remove the mic parts from the housing to have room to work. Anybody have experience with this being a bad idea, based on the way dynamic mic parts are installed in housing in the factory?

Click to expand...

It really depends on the mic. If you pull against the magnet wires up near the capsule and break them your mic can be ruined. The diaphragm as well is very delicate.  But sounds like you need to take it out to repair the rear connections.
Might help if you posted a picture.  There is a heavy red wire that should come out to a pin for plugging into the filter.  I attached a pic I found that shows the rear connections that is from an ebay listing. Butif I understand correctly you are trying to repair the connections on the back side of this circuit board.

dmp said:

It really depends on the mic. If you pull against the magnet wires up near the capsule and break them your mic can be ruined. The diaphragm as well is very delicate.  But sounds like you need to take it out to repair the rear connections.
Might help if you posted a picture.  There is a heavy red wire that should come out to a pin for plugging into the filter.  I attached a pic I found that shows the rear connections that is from an ebay listing. Butif I understand correctly you are trying to repair the connections on the back side of this circuit board.

Click to expand...

Correct. This is the amount I can comfortably slide out until I hit some type of strain (and I hope this alone is not too far). I believe what I'm seeing is the main filter PCB, with the transformer in question. Tough to see how I can get it farther than this, but I at least have access to the one PCB i need here.

dmp said:

Butif I understand correctly you are trying to repair the connections on the back side of this circuit board.

Click to expand...

Here's a shot of the terminals behind the EQ jumper panel you posted a pic of. This is where I'd like to sort out the positioning of my transformer wires. I have a green, a white, and a yellow that need to be connected, in addition to the black and red (second red, same diameter as the green) which are already connected. I may just replicate the order that they are in on the PCB below.

You can see the filter components (RCL components) so you could  sketch a schematic.

I would guess you have four transformer wires coming from up in the mic (C, 50, 150, 250) and then the filter components are switched in via the back panel connections.