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-   -   MINI A: who let the smoke out. (http://www.diyaudio.com/forums/pass-labs/141011-mini-who-let-smoke-out.html)

d to the g 23rd March 2009 06:03 PM

MINI A: who let the smoke out.
 
So, I was powering up a mini aleph (Brian GT boards) this weekend.

I hooked up +12V to the +V hole, and -12V to the -V hole.

I then hooked up the +0V cable to the +G, and the -0V to the -G.

I then powered up, got some strange reading fluctuations... then a small amount of smoke.

Nothing seems burned on the board, no parts melted, nothing obvious.

Looking at some pictures, I found an image of the mini A on briangt's image gallery with the 0V line hooked up to the output ground, which does NOT directly connect to the +G or the -G.

There may have been a small amount of rosin left on the board after cleaning with isopropyl. The smoke was pretty faint, and blue like solder smoke. Could it have been a microscopic amount of rosin on the board?

So;

1. What parts do I need to replace?
2. What are +G and -G for, if not for the 0V signal? I've built PD's chipamps and that was exactly what these pads were for.
3. Is this common to have the 0V line on the same pad as the signal ground?
4. Thanks in advance.

MEGA_amp 23rd March 2009 10:51 PM

BrianGT Aleph boards:


-G,+G = Gate; they're only used if you're using the output boards, For MiniA, these are not used. Gnd (0V) and signal gnd (CGND on the board) are the same. Circuit Gnd should be isolated from Chassis/Earth Gnd via thermistor or a bridge rectifier. I'm not sure the effects of putting the 0V line into the gates, but if you saw smoke, I would remove fets and test, and check/replace Q4,Q5. Sometimes smoke pours out and upon close inspection it may appear OK, when it isn't.

Bill Fuss 24th March 2009 02:13 AM

I'm pretty sure you let the smoke out of Q5, and they need that smoke to operate correctly.:D I haven't figured out how to get it back in so I would replace it, but check everything, there aren't that many parts anyway.
Bill

d to the g 24th March 2009 03:47 AM

Any chance I could test these without desoldering the whole board using the VGS testing method prescribed in the "diyopamps" article?

edit: desolder half the board

Bill Fuss 24th March 2009 01:37 PM

I was trying to work from memory and misspoke about Q5. You can do some basic checking if you disconnect the board from the PS completely. By putting the PS ground on the gates you put the rail voltage across R14-16 which should be OK, but check them anyway, and R18, which is probably where the smoke came from. You can check for shorts across the output fets from drain to source in both directions with a ohmeter.
I'm looking at the schematic from BrianGT, if you need it I can send it to you.
Bill

d to the g 25th March 2009 05:01 PM

Bill, I've emailed you for the schematic.

Bill Fuss 25th March 2009 05:10 PM

I sent you the PDF yesterday, I'll resend it.
Bill

d to the g 27th March 2009 09:22 PM

Bill, didn't see your email (even checked my spam filter). However, I used the way back machine and downloaded briangt's schema.

ps. replaced Q4 and am listening to music.

Bill Fuss 28th March 2009 01:49 PM

I just sent a test email to you.
cheque1two@hotmail.com is what I get when I use the forum mailer from my email.
Glad to hear you're up and running.
Bill

d to the g 28th March 2009 03:32 PM

Thats the email I use for the forum, but nothing showed up. Too weird.


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