Help with replacement capacitor shopping

[Mp3]

Hi everyone,
i have an audio interface here i got for almost nothing. It works fine when it works, but it randomly resets or powers off. I opened it up and found two of the three biggest capacitors are domed so i think i should replace them.

The capacitors are 2x 4700uf 10v  and   1x  1000uf 35v

The problem is the capacitors used have no name or info aside from capacitance and voltage.  I can't easily pick a replacement capacitor since i don't want to choose one with an incorrect ripple current rating and cause more damage.

How can i find out if there is no easily found information on the capacitors used in the device? If the ripple current is around 2A for my replacement caps is there much risk?

Thank you!

[ArthurDent]

I wouldn't worry too much but to be safe just get low ESR 105 degree C rated caps. They aren't much different in price from the ones that were originally used that are probably cheaper ones if they aren't marked.

[james_s]

The capacitors you're replacing are probably not anything special, don't over-think it, just buy something from one of the reputable brands following the advice above. Personally I like Nichicon, Rubycon and Panasonic capacitors but those are far from the only good choices Virtually anything from places like Digikey will be better than the generic crap that is in there.

[Old Printer]

Since the obvious hasn't been stated, I think what you are referring to is electrolytic as the type of capacitor. If your original caps have a polarity marked on the case, electrolytic is the moset probable, though tantalum capacitors can also have a polarity designation. A pix would help.

[TERRA Operative]

A small detail to note.

Capacitors these days are much smaller than older caps with the same ratings. This means you will often need to go to a higher voltage rating capacitor so the leads on the new capacitor will fit the spacing of the holes on the PCB.
As long as the capacitance is the same, you can go higher voltage no worries, just don't go lower.

Any low ESR cap from a reputable manufacturer will be fine. I like the Rubycon ZL/ZLH/ZLR series for low ESR and low ESL (Equivalent Series Inductance) with high ripple current ratings.

[ArthurDent]

"Since the obvious hasn't been stated, I think what you are referring to is electrolytic..."

When the OP says: "...found two of the three biggest capacitors are domed", we know that these are board mounted radial electrolytic. One thing to keep in mind as well is that the oxide layer that is formed by anodization is affected by the voltage across the electrolytic capacitor so using a capacitor of a much higher voltage rating than the original may give you a smaller capacitance that the rated value. Because of this oxidation layer difference if you use a higher voltage rated capacitor you probably will get a higher ESR from those replacement caps compared to the original.

The good news is that in a power supply if the caps are used on the secondary side for filtering, the capacitance value probably isn't that critical, and in the design they probably use the smallest (read cheapest) cap they can in that location. If the caps were domed then probably they were losing capacitance over time as well before they got to a point that they gave you problems so the capacitance isn't that critical.  If the spacing on the replacement cap is different I generally try to replace with the same voltage rating and make the spacing work.

[t1d]

I am e-recapping a 27 year old PSU.

I have been doing a bit of reading and I am still confused... All other perimeters being equal, do I want to buy the e-cap with the highest stated ripple, or the lowest? I am looking at Mouser search results.

The confusion is whether the stated ripple is either
1) the amount of ripple allowed to get by (if so, you would want the lowest rating,) or
2) the amount of ripply stopped (if so, you would want to buy the highest rating.)

Thank you for your help.

[TERRA Operative]

You wwant the highest value you can get, the ripple current rating is what the capacitor can withstand.

More ripple current rating, more betterer.

[bdunham7]

You might want to post a photo and/or tell us exactly what the device is.  In audio, it might be possible that those 4700uF caps are bipolar, although that's really unlikely.  And as others have said, anything you can fit in there will likely work fine, so your most critical specs are lead spacing and diameter!

[t1d]

Thanks, folks... That gets it cleared up.

[Electro Detective]

A 27 year old device more than likely has decent quality standard capacitors in it.

Having learned the hard way a few times, I would avoid the 'buy better' mindset and get exactly the same values and voltage ratings 
and 85 degree ones if that's what was in there, as the last lot lasted years and years...

Buy reputable brand caps and you're set 

If the caps are near heat sources, get 105 degree rated ones with closely similar specs to the 85 jobs

I'm assuming you don't want to play upgrade mod engineer  and just want that device rocking 'day one' again asap, right? 

[t1d]

A 27 year old device more than likely has decent quality standard capacitors in it.

Having learned the hard way a few times, I would avoid the 'buy better' mindset and get exactly the same values and voltage ratings 
and 85 degree ones if that's what was in there, as the last lot lasted years and years...

Buy reputable brand caps and you're set 

If the caps are near heat sources, get 105 degree rated ones with closely similar specs to the 85 jobs

I'm assuming you don't want to play upgrade mod engineer  and just want that device rocking 'day one' again asap, right? 

Thanks for your help, Electro Detective... Yours is good advice and I know the reasons why.

I just completed my order at Mouser. I try to stick to Nichicon and Panasonic, but for one item I had to stray, because it just wasn't available... The original is Illinois Capacitor and that is what I ended up with as its replacement.

The big mains caps are dead on for all specs, except their height is lower, due to better cap technology. And, I bought a high ripple rating. 2.6a, IIRC, the original being unknown.

The other caps are dead on for uFs and pin spacing. Diameter and height are what can be accommodated. Voltage was allowed to vary upward. My thinking was that inrush was more important for the big supply caps and not so much for the other caps. Let's hope I don't fry an op amp, or such... And I bought high ripple ratings. Hours, too.

Because of the nature of the job requires better quality and there are just a few caps, meaning it can't add up to much, I did not skimp on quality. Total OTD was about $21USD for 13 caps.

If you think I can get in trouble on the inrush current, please let me know. I appreciate everyone's input.

P.S. I am thinking of doing a repair thread, when the parts arrive.

[Electro Detective]

Hey, no shortage of repair thread junkies here (guilty as charged  ) 

FWIW I've got four identical suss power supplies to dig into soon,
and know that one of them has the original caps that lasted many many years, and finally clapped out, causing audio hum. 

whereas the other three were recently re-capped, apparently with 'good enough' and or 'better' caps, and already in a short while producing audio hum.
Two were spares that were used a few times and sat on a shelf, seems like the caps thought they were batteries and died anyway   

So...the plan is to work out which of the four has the original cap work, sort of try to replicate what was fitted at the factory, 
verify that all is good using quality pre-tested caps. 
then do the other three if it's a go, which I'm confident it will be, been there before 

[paul8f]

Great advice in the replies to this one!

I'd agree with aiming to keep as close as possible to the original component specs. If unsure, aim for a low-ESR rating, 105deg temp rating and obviously no lower than the original max working-voltage.

Before installing the replacements, test the new caps with a quality meter such as the Peak Atlas ESR70 (just because a component is new and shiny doesn't mean you didn't get shipped a dud!   )

If you need to bend the legs to align with PCB holes, then after soldering support the new cap with a dab of hot-glue or Silastic compound. Also after soldering, don't forget the basics like using flux remover to clean the flux off, and also making sure that the new cap has the same orientation as the one removed (don't rely totally on PCB markings denoting the NEG side... on very rare occasions the silkscreen/soldermask symbol is incorrect...yes I've seen this firsthand.)

As a side note... in my collection I have yellow Nitai non-polarised (bipolar) 100uF electrolytic capacitors, so just remember these do exist. Good luck with the repair 

[Electro Detective]

before you hit that buy button because it is a cheap 105C rated 5khrs etc etc, make sure to measure the size that it fits.

all those damn sites have huge "add to cart" buttons but most crucial size data are right way way at beyond screen view 

Yeah, no physical dimensions    =  no Buy button click, dump the shopping cart, and the Finger at the checkout robot