Oh Dear...Replacement needed for Caiman big smoothing cap?

[Gazjam]

Oh dear, what a nasty experience I had the other night.

Tried a new Linear PSU which runs at 15V 3A on my Dac last night, a
trial from a good guy on AOS.
It has a +-10% variable voltage which can be adjusted.

Anyway, hooked it up with a meter of Mark Grants mains cable and sat
back to enjoy.
Checked wiring was OK then checked again.

After a couple of minutes a strong smell of ammonia(?) coming from the
Dac and a crackling noise...
Shit!
I powered off right away, only to notice that the Dac was red hot where
the big smoothing cap was?
oh dear..

Left the case to cool and opened up the lid.
The big smoothing cap had swollen and had been "sweating" inside the case!
The PCB was covered in some kind of slick coating and it stank of
ammonia or something.

Leaving the Dac to cool, I got the multimeter out and tested the voltage
on the power supply.
Its 15v +-10% so should have been OK?
Nope - it was reading 31V!!!
How is this possible?

Something must have happened to the PSU it in transit - I have no idea what.
Adjusting the voltage +-10% screw though got it down to 15.6V...what it
should have been.

I should have double checked BEFORE I plugged it in, lesson learned!


Thinking my Dac was knackered I hooked it up hours later once the Dac
(and myself) had cooled down and knowing the supply was working as it
should at 15v+
The Dac worked but with a few problems:

1. The input selectors didn't work properly. No matter what you selected
it only played Coaxial#2.
2. The Optical input didn't work.
3. Sound quality had suffered - not anywhere near as good as before
prior to the big smoothing cap going ppffftttt.

Pretty pissed off I went to bed, thinking to look at it again in the
morning.

Everything works!
The sound quality is not what it should be but I suspect the burst
smoothing cap is the problem?
I'm guessing the Dac had overnight to "dry out" and fix itself?


SO...
from a position of "improving" my linear PSU I'm now 2 steps behind
where I was before.


What's the next move Guys...
My next mod to the Dac after improving the PSU was to replace the big
smoothing cap with a film cap, so maybe its the ideal time to look at it
- a blessing in disguise?
(I use Murata regs in my Dac, which has all the mods done and Gator
board fitted).

Should I be worried about anything else having went pop - everything
seems to work and the heat was only coming from the smoothing cap?

The Dacs unplugged till I can get this sorted.

Thanks.

[StanleyB]

One good and unique thing about my DAcs is that they have a dual power supply. One is external and one is internal. So it is more robust that most of the other ones out there .

Replace the power caps with say 6800uF 25 or 35V after checking that they are not higher than 30mm.
The audio PCB might have gone down as well. I am out of stock of the Gator as I was going to stop selling them as an upgrade. But I have 20 on order for some folks who missed out. You can go on the list for one.

[Reid Malenfant]

If i was you i'd clean the PCB up as it sounds like it's got a lovely coating of electrolyte all over it, that's possibly another reason it's not sounding as it should..

Not sure what to recommend to clean it up all all honesty, possibly Isopropanol would shift it. You should be able to buy some at an independant chemists. If they ask you what you want it for say cleaning tape heads

[chrism]

If the new linear PSU has a good quality smoothing cap you don't need another in the Caiman. I found that 10,000uf in the PSU did the trick and added a small tant in place of the large Caiman cap. I prefered the sound with the little tant in place rather than another large cap.

Lucky escape BTW!

Regards

Chris

[Reid Malenfant]

I guess i should add that electrolyte is conductive & will rot the PCB given enough time You wouldn't believe the amount of knackered SMPS PCBs i have seen that have been eaten away by electrolyte from leaky capacitors

I'd make it a priority to clean it ASAP, before you use it again!

E2A:- Isopropanol is the same as Isopropyl Alchohol, it's the purest alcohol you'll be able to purchase legally as a member of the public..

[Gazjam]

Thanks guys..

The supply I have is THIS: NNS-15
http://www.tdk-lambda.com/products/s...ns/indexe.html

would it have a smoothing cap in it somewhere?
I cant really tell from the specs to be honest

Chris:
What Tant did you fit?
Can you remember the specific one, just so I know what to buy.
I know you can replace the smoothing cap with a film cap..would this be better?

Mark:
The Dac is OFF till further notice...will pop into the chemists and clean the board ASAP.
Would a cotton bud be ok for this Mark?
thanks for the info.


Stan:
As the Dac still works..I suspect the blown cap still functions....can I take it that the main PCB/Gator is actually OK as Im getting sound from the Dac?
If the blown cap is replaced, will the Dac be at 100% sound quality of what it was...or will there be a reduction?

If I give the board a cleanup with isopropyl alcohol and replace the swollen smoothing cap, would I be good to go or should I maybe get the Dac checked out properly to see if theres anything wrong deeper down?
Would this be something you could look at Stan?
thanks.

Not had this happen to me before, so unsure of the best way to go about it.

Thanks.
G.

[Reid Malenfant]

Yes it'll have a smoothing capacitor inside it...

If i was you i'd fit something like a Sanyo Os-con which has super low ESR.

If the DAC still functions it'll probably be 100% OK after cleaning with isopropanol. Use a clean paintbrush & tip some on the PCB & give it a gentle scrub. Make sure you remove all traces of electrolyte as it'll eat into the PCB & start making connections where there shouldn't be any..

Not only does the stuff eat in but it connects things that shouldn't be as i mentioned. I'd often find charred sections of PCB under leaky caps. This was caused by the electrolyte conducting between the two pins of the cap & making things get hot due to excessive current flow - which of course just made the whole thing worse

[chrism]

Hi G,

The cap, tant or film cap value is really is not important so try whatever you have. The tant I had in was a small one and the film cap I have in now is also tiny. I found that using a 10,000uf in the PSU and a 10,000uf in the Caiman gave a sluggish sound (over smoothed possibly) and a little tant or cap corrected this. I only put a cap in to address potential RF or I would have gone with nothing in the Caiman.

Regards

Chris

[Gazjam]

Yes it'll have a smoothing capacitor inside it...

If i was you i'd fit something like a Sanyo Os-con which has super low ESR.

If the DAC still functions it'll probably be 100% OK after cleaning with isopropanol. Use a clean paintbrush & tip some on the PCB & give it a gentle scrub. Make sure you remove all traces of electrolyte as it'll eat into the PCB & start making connections where there shouldn't be any..

Not only does the stuff eat in but it connects things that shouldn't be as i mentioned. I'd often find charred sections of PCB under leaky caps. This was caused by the electrolyte conducting between the two pins of the cap & making things get hot due to excessive current flow - which of course just made the whole thing worse

Thanks again for the info Mark, sounds do-able.
Would you suggest a particular Sanyo Os-con for this job?

Seems the choice isn't all that critical, but as I dont have any caps lying around I'd need to order one in anyway..might as well get something good?


Thanks.
G.

[Gazjam]

Hi G,

The cap, tant or film cap value is really is not important so try whatever you have. The tant I had in was a small one and the film cap I have in now is also tiny. I found that using a 10,000uf in the PSU and a 10,000uf in the Caiman gave a sluggish sound (over smoothed possibly) and a little tant or cap corrected this. I only put a cap in to address potential RF or I would have gone with nothing in the Caiman.

Regards

Chris

Cheers Chris, good info.
Gaz.