incompatibility issues when mixing V1.4 and V1.6.1 ?

[limey222]

I purchased a chassis last year with a combination of pres installed. This week I did a swap with another owner. He took one of my N72's and I took one of his A12's. I alreday had one A12 in my chassis and it was a V4.0. The newly arrived one is a V1.6.1 and I notice some significant component differences between the two. I installed the new one but all I get out of it is a very low, distorted signal while my original A12 passes audio beautifully. Is there a compatibility issue going on here?
I know a little history on the A12 I have just received, the seller told me that it was originally purchased by a guy called H. Duncan, who apparently had some problems with the asembly so he retrurned it to SCA and they finished off the build, tested it and returned it to the owner. Now i have inherited it.
So what could it be incompatibility or a problem pre?

[tpryan]

There are more features supported on the newer revisions, but there is no incompatibility. If you swapped a working N72 for a faulty A12, I'd try to get my working module back if I were you.

[jdier]

Hey Tim,

That module came from me. I bought it from hduncan and it worked fine for me when it arrived here from Hawk.

Michael and I did the swap and his card worked fine here in my chassis.

It sounds like I either bumped something while pulling the card (however, I was super careful and followed the instructions you pointed me to) or it got damaged in shipping.

Again, it worked prior to hduncan shipping to me, it worked here for me, then once it got to Michael it was not working.

This card will wind up getting fixed one way or another so it seems crazy for Michael to ship it back to me just so I can diagnose it or possibly wind up shipping it back to SCA.

Curious if there are any first pass things you can recommend Michael look at on the non working card to see if he can get it working? Michael says it just barely passes a signal and that there is a lot of noise (unusable.) We may wind up shipping the card back to you to have it repaired.

either way, I wanted you to know that we were in this together and want to find a solution.

[limey222]

Thanks for getting back to me, so if I rule out incompatibility then the pre must have suffered some damage on its way to me. The best way I can describe to you how it sounds when I try to pass audio is that if you can image listening to a really small transistor radio at low volume, If i turn the gain all the way up then I start to get a low frequency hum as well.
I can't see any apparent damage on the board, no tracking marks or suspect solder joints.
The simplest way to resolve the problem which helps both Jim and myself since I want to end up with a fully functioning A12 and not just get my N72 back from him is ask you what it would cost for you to repair it for us. Then Jim Dier and I can work out some sort of arrangement

[tpryan]

Try following the initial power-up procedure in steps 30 to 36 of the assembly instructions. You should be able to measure the voltages indicated.

If the noise/hum increases with each gain step but the module does not pass a signal, the amplifier is probably working but there is no input signal. Try re-flowing the solder joints at the input XLR and input transformer.

If that doesn't work, send an e-mail to rma@seventhcircleaudio.com for return instructions.