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Author Topic: Noise from mix bus..somewhere..
Paul-
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 17:37

<div class="cosmo-blockquote "><p>Quote from maikol on May 9, 2016, 12:47
Hmm so the issue is on the input/output board... interesting !
And yes again, obviously there is some part on this board too that lies after the fader/mute.</p></div>

I've just desoldered the caps on the board. Hardly used the desoldering gun before so it took a while to get the grip, but the final 20 or so gave up really fast so all smiles.
Maikol, a couple of questions about desoldering..
- I got the best results putting the PCB in a vice and twist the component lightly while desoldering, and pull it out while desoldering the second leg. Sounds ok to you or would you suggest another method?
- What temperature would you recommend?
- Are you careful and not touching the ICs on the board? I found it hard to avoid..
maikol
Administrator
Posts: 77
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 18:06

Yes that is how I ended up doing it too.

Holding the PCB in a vice, I started by removing the soldering completely on the first leg, and by grabbing the cap with your free fingers you can feel it starting to get a little play when the first leg is freed.

What does your desoldering gun look like ? Hollow tip with a vacuum pump ? If that's what you have, and you have several sizes of tip holes, find the one that fits just fine around the caps legs on the back of the PCB. It should quickly melt the soldering by pressing gently on it. As soon as it seems melted you can use the pump to remove it.

I did find that with my gun, it was best to wait for the soldering to be really melted before activating the vacuum pump (I guess the flow of air colds the metal down, so it better be hot enough and already melted).

Once I got quick enough with my removing technique, I think I ended up pretty high in temperature, making sure I wasn't staying too long in contact with the copper tracks.

Be careful not to damage the little copper donut shaped track around the component's leg, which can happen if you heat it too much, or if you pull too hard on the component you're trying to remove.

Oh, and if you don't get all the soldering out of these holes, sometimes it's better to add some back on it to help melt it and remove it quickly.
Paul-
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 18:46

Great!
Excuse me Maikol, one more..
What's the deal with the other caps, film and ceramics, do they last much longer than the electrolytics?
maikol
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Posts: 77
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 18:51

No problem mate! :-)

Yeah the film and ceramics ones are supposed to last much longer, and unless you're looking to upgrade these (then I would recommend talking to our great Shawn ;-) ), I would just let them there.
Paul-
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 9, 2016, 19:23

Cool. Yes, I've been drooling many times over Shawn's article
Paul-
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 12, 2016, 15:49

Maikol, I got the caps today. As I just copied your list I didn't notice until now that the 220µF caps are only 10V. They are also smaller in size than the original caps. I thought the execution racks operated at 15V... So shouldn't I move up to 25V tolerance?..
maikol
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Posts: 77
Post Re: Noise from mix bus..somewhere..
on: May 12, 2016, 15:54

Yes these caps are a bit smaller than the original ones, but they are said to actually be better.

And about the values V or uF, I just replaced the original ones with exactly the same values. Not being competent enough in electronics, I did prefer to play it safe... ;-)

Paul-
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: May 12, 2016, 16:45

The way I've learnt the Volt specs on caps is the tolerance, meaning how many Volt they take before breaking, so never any risk going for a higher value. Just as you say the original 220µF caps are 10V. Makes me curious though.. Seems a bit low.. I'll ask around before going ahead and recap all channels. The ELNA audio caps that Shawn mention also looks tempting! 4 x more expensive and also larger so a lot of work making them fit. I'd love to try doing a pair of channels with those to see if it would be worth it putting them in channel 1-24 for instance.
Paul-
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Posts: 62
Post Re: Noise from mix bus..somewhere..
on: June 27, 2016, 08:24

Ok, so a follow up on this issue. I recapped the electrolytics on the bad I/O card but the noise was still present. As I have a couple of spare channels I decided to stop searching for the bad component and instead replaced the whole board, and the problem is gone.
maikol
Administrator
Posts: 77
Post Re: Noise from mix bus..somewhere..
on: June 29, 2016, 08:35

So it was on the I/O card, but not a bad cap problem... hmmmm... maybe one of the 9532 chips has fried then ? :-/
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