why dead input transformer?

[aronaut]

Hello all, looking for some troubleshooting help...

I built 8 channels of NYDave One Bottles as can be seen in this thread:
http://www.groupdiy.com/index.php?topic=45990.msg576355#msg576355

They're working perfectly and I've been recording through them for several weeks now. after the first few days of use one unit stopped passing audio. I went through the whole circuit and discovered the input transformer (Cinemag CMMI-10PCA) was no longer operating. I switched it out with another transformer and that unit is working fine now, so the rest of the circuit seems to have no issues. Why would the tranny stop working? I'm no longer getting resistance readings from it.
could it just be faulty? what should I look out for?
The circuit board hole tracings are on both sides of the card, perhaps the tranny was seated such that the can shielding was shorting itself out on one of the pins, could that fry it?

any help greatly appreciated
Thanks
A

 

[desol]

Something could've come loose inside...not entirely impossible. Take it apart...it'll be fun!

 

[gemini86]

I would contact cinemag, maybe they'll be gracious enough to swap it?

Couldn't hurt.

 

[mitsos]

That is a seriously nice build.

The circuit board hole tracings are on both sides of the card, perhaps the tranny was seated such that the can shielding was shorting itself out on one of the pins, could that fry it?

yes, shorting a winding to ground is pretty much instant death for a transformer. You are one lucky guy, it could have been 8 trafos.

At first I couldn't see any problems in your pics, but as you say above, you have plated through holes on the PCB, so, I'm assuming, under the transformer as well? As I have found out first hand (and now you too!), you should leave some space under a metal trafo any time you have plated through holes.

I highly recommend you turn this thing off and not use it until you: remove the transformers, stick a piece of double sided "squishy" tape under each one and reinstall.  Cinemag sometimes sends out little plastic isolators with orders, maybe you got some with your trafos?

good luck, and be happy you didn't kill all 8!

 

[aronaut]

Awesome, that's what I suspected. switching on the soldering iron now.
Thanks!
A

 

[emrr]

yes, shorting a winding to ground is pretty much instant death for a transformer.

What, from phantom power?  Only thing I can imagine. 

 

[mitsos]

You're probably right.  These being mic amps, it was probably phantom, but I  think it would be possible for a high line signal to kill an output trafo, for example.  But I'm not going to try to reenact the situation!