uh, and i ******* up again, caps and rectifiers got ugly warm - dead? - diyAudio
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Old 12th February 2005, 09:52 PM   #1
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Default uh, and i ******* up again, caps and rectifiers got ugly warm - dead?

Yes, i suprise myselfe sometimes with how much it's possible to mess up such a simple litle thing as a gc, but i managed to do it again.

what did i do this time?

i grounded the "+" on the rectifier and tried to use the "-" as a source for negative voltage.

what happend?
the rectifier and the main resiervoare cap got dirty hot, and I pulled the plug on the amp.


question:
is the cap and rectifier dead? would it be wise to trie to use them again?
have i killed the lm3886 to at the same time? it's well protected isn't it?
and the opa627's too..

Regards
Marius
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Old 12th February 2005, 11:03 PM   #2
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You must correct the error and try again.
Measure everything, including DC-offset, before connecting any speakers.
Oh, you better wear sunglasses before switching on.
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Old 13th February 2005, 12:01 AM   #3
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Carlos, are you serious?

correcting the error? trying again?

well, the problem is, i dont know what i did wrong, and i dont see or measure any wires where their not suposed to be..

I was a litle tired when i wrote the previous post, so to clairify:

can i connect the "+" out of one of the rectifiers (hereby refered to as nr1) to the others(nr2) "-" and take negative voltage off the "-" of number 1?

edit: ok, just to impress you all with my morvelouse paint skills..
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Old 13th February 2005, 12:30 AM   #4
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Quote:
Originally posted by demogorgon
edit: ok, just to impress you all with my morvelouse paint skills..
That is correct.
Check it out if you have made it as the sketch.
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Old 13th February 2005, 01:42 AM   #5
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now, i checked, and checked again, but this thing is still acting so wierd..

could it be that the cap is shot, and that there is contact to some extent inside it, why in the hell would it get hot otherwhise?

this thing is bugging me out..
the lm ic's seem fine though, getting warm, but nothing more than a lm3886 turning on for the first time is supposed to get..

BAH!!

thanks
marius
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Old 13th February 2005, 03:00 AM   #6
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heh, the **** cap was shot as i hoped. now for resoldering it all again

this buffer better be woth it carlos..
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Old 13th February 2005, 04:28 AM   #7
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not the cap after all!

i replaced it with a new one, but nothing: still gong warm.
what is cousing this? everything is in order!
every solderjoint to itself, every wire where it's supposed to be..

I have to constantly battle my self and my own crazed desire not to pick it up and smash it to the wall.

can anyone me some pointers as to what to look for?

regards
marius
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Old 13th February 2005, 04:42 AM   #8
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Sorry to ask this question, but have you double checked the polarity of your caps? (the simple errors are often the hardest to see)

The one on the +ve rail should have the -ve on the zero volts line, and the one on the -ve rail should have the +ve on the zero volts line.

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Old 13th February 2005, 04:53 AM   #9
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Hi Demogorgon;

Hmmm, just some ideas, based on my (possibly faulty) understanding of your situation -

1. Are you sure that the parallel primaries of your PS trafo are wired in phase with each other?
2. Did you wire the 2 caps so that the "lower" one has it's "+" attached to the "upper" one's "-" at the system ground? That's the way it should be.
3. V- isn't attached to system ground, is it?

On a circuit like this, having a pair of cheap DMM's with alligator clip leads is nice, since you can measure both secondaries at once and you don't have to worry about reversing phase so much. I picked up a $20 Chinese cheapie DMM to go with my (somewhat better) Chinese cheapie DMM for just this sort of thing....

One last thought is to wire and debug the PS circuit before the amp - that way you won't risk pricey chips un-necessarily.

Good luck!
All the best,
Morse
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Old 13th February 2005, 04:59 AM   #10
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Just one comment on morse's last suggestion. Make sure that you have a safe way of discharging the PS caps if you don't have a load connected! I normally use a standard 60W house light bulb, with some wires soldered to it.

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