smoking R28 !!

[gradwellhouse]

i assembled 2 A12 pres over the last 2 days. I had some serious issues assembling the 1st unit after i put the voltage regulators in the wrong spots. I realized my mistake right away but desoldering a 3 pin part was not easy and i think i may have cooked the contact on the board while doing so (the silver ring on the board is now gone or the solder just wont grab like it should). I got the rest of the a12 together fine and when i plugged it in i got smoke. It came from R28 which has some scorching on it but still worked (still gave the correct resistence reading when tested).
Would a bad contact on the board cause this? is there any solution to fixing the board or jumping the connection?

steve

p.s. the unit i did 2nd went together flawlessly and is installed working fine.

[bradb]

my advice is, look for incorrectly installed components, wrong polarities on caps, etc. Check everything. if everything is good, flip your board over and start looking for shorts, solder bridges etc.

if you've lifted the pad, you may be ok, as long as you can make contact with whatever that pad was making contact with on that side of the board. the holes are plated thru so you should have connection to the top side of the board. with some careful soldering you can reconnect the component leg to wherever its supposed to go.

sorry its not much but its a start!

[gradwellhouse]

i triple checked all the components and solder joints. It all looks good to me. Could i have "cooked" the VR when i was tryng to de-solder it?
is there a way to test that part to see if i did?

[gradwellhouse]

Tim, I have tried calling you and emailing you multiple times. Could you please call me? 856-287-4094
i mailed you my preamp for repair almost 2 months ago and i cannot get ahold of you.
Steve Poponi

[analogical]

Any word on how this was remedied? I am having the same issue.

[gradwellhouse]

I think I had the 2 VRs in the wrong spots. Make sure you have the right ones in the right spot. I triple checked and still missed it. Quadruple check i guess.
Steve

[analogical]

Comparing my VR's with my not working v1.4 A12 and my working v1.6 A12, I see that they are not entirely similar:

R25&R29 on the working pre reads:

617c Y102

However on the 1.4 pre the VR's read:

725c0 Y102

Does this matter?

Honestly having been sent a mixed revision kit has been a real headache.
relying on a 1.6 bom to build off a 1.4 board with 1.6 parts has not been breezy, specially for a newb like me.

I'm having the same prob as gradwellhouse, a smoking R28 but no visual evidence of shorts or cold joints.

Anyone have any advice?

[tpryan]

Does this matter?

Nope

Honestly having been sent a mixed revision kit has been a real headache.

Sorry for the confusion, but from our point of view they seem so similar as to hardly require changing the instructions. The old docs are still up on the server, just change change "A12R16" to "A12R14" in the url, like so: http://www.seventhcircleaudio.com/A12/A ... 12_sch.pdf

smoking R28

The only way to get a 15K ohm resistor to smoke is to put more than 60V or so across it. I suspect you've got a 150 ohm in its place.