API clon going the wrong way

http://www.groupdiy.com/index.php?topic=32028.0
After designing the board in the topic above I have some trouble with one of the channels.

schem
http://www.groupdiy.com/index.php?action=dlattach;topic=32028.0;attach=273;image


After I thought it was the opamp I was so luck to resive some new one from Black Dog. Changing it and it ran for about 10 min. I heard some clicks and the 470uf after the opamp made a leakage.
What the hell is wrong?  ??? ??? ??? ??? : :-[ :'(

I have an identical twin next to it and that works perfectly...

Cheers
Soeren

Measure DC offset at the opamp output with respect to ground. Double check the cap was the correct way around.

rodabod said:

Measure DC offset at the opamp output with respect to ground. Double check the cap was the correct way around.

Click to expand...

On the working channel the offset is 0.08v and on the not-working without the 470uf (I don't have any spare right now) it is 0.06v

Is it okay?

Soeren_DK said:

rodabod said:

Measure DC offset at the opamp output with respect to ground. Double check the cap was the correct way around.

Click to expand...

On the working channel the offset is 0.08v and on the not-working without the 470uf (I don't have any spare right now) it is 0.06v

Is it okay?

Click to expand...

Yes.

In that case, check the other end of the cap was definitely going to 0V (ground).

rodabod said:

Soeren_DK said:

rodabod said:

Measure DC offset at the opamp output with respect to ground. Double check the cap was the correct way around.

Click to expand...

On the working channel the offset is 0.08v and on the not-working without the 470uf (I don't have any spare right now) it is 0.06v

Is it okay?

Click to expand...

Yes.

In that case, check the other end of the cap was definitely going to 0V (ground).

Click to expand...

What cap? the 470uf?

Soeren

Yes. Caps tend to leak only when being overvoltaged severely.

Svart said:

Yes. Caps tend to leak only when being overvoltaged severely.

Click to expand...

The cap could take 25V so how should it be overvoltaged?

After a sleep I have to questions.
What can you see when you measure the DC offset? What could be wrong when measuring a false DC offset?

Why is 470uf/25V cap there?

Cbeers
Soeren

EDIT:
I replaced the cap with a spare I found at my fathers house and now it seems to work fine. That pretty weird. Could a bad cap has caused that a DOA got toasted?

The capacitor thing happended to me just yesterday. I set up an old computer I had stored in the loft; hadn't used it for a couple of years. Within 3 seconds of switching it on, I got a loud bang. After switching it off and pulling the mains plug, I set about trying to trace where the bang (and the strange smokey aroma) had come from - turned out it was a capacitor on the motherboard.

After looking into this on the interweb, it seems that some industrial espionage occured a good 3-4 years ago at an eastern capacitor manufacturers; a chemist left a capacitor manufacturing company and went to work for a rival. He replicated the 'magic' electrolyte formula from his previous employer and tons of capacitors got manufactured. Problem was, he got the formula slightly wrong, and the capacitors degrade prematurely, eventually creating hydrogen, and as current is passed through them, a loud bang!

Many motherboard (and other equipment) manufacturers got their fingers burnt because of this and much equipment is still out there with leaking (and blowing) capacitors made by this firm, including 'rebadged' ones that counterfeiting companies used to rebadge as expensive competitors' capacitors.

Sound very James Bond, but according to news articles is true!

Also, check out here: http://www.capacitorlab.com/index.htm and here http://www.badcaps.net/pages.php?vid=4

Soeren_DK said:

The cap could take 25V so how should it be overvoltaged?

Click to expand...

I don't know.

What can you see when you measure the DC offset? What could be wrong when measuring a false DC offset?

Click to expand...

The DC offset is just the DC voltage present at the output of the opamp. We'd rather it was 0V DC with respect to ground, but we live with it. I don't understand the last part of your question.

Why is 470uf/25V cap there?

Click to expand...

To block any DC from passing through the transformer primary. The transformer doesn't like DC.

Thanks guys.

I don't understand the last part of your question.

Click to expand...

It was a hypothetical quastion. If the DC offset had been 1V DC. What could that have indicated?

Cheers
Soeren

Soeren_DK said:

I don't understand the last part of your question.

Click to expand...

It was a hypothetical quastion. If the DC offset had been 1V DC. What could that have indicated?

Click to expand...

Possibly a dodgy opamp.

Thanks

The last quastion in this round. Why should the cap be 470uf and not 100uf?

Cheers

Soeren_DK said:

The last quastion in this round. Why should the cap be 470uf and not 100uf?

Click to expand...

The cap forms a high-pass filter. The cut-off frequency is set by the value of this cap. Bigger cap = lower cut-off = more bass response (usually).