Capacitor advice needed

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rensjepensje

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Hi, this is my first post at groupdiy. I'm just starting out with electronics and I just finished my first diy mic kit from mic-parts with great enjoyment and succes. I watched a few courses on basic electronic schematics and I'm going to dive into 'The Art of Electronics' because I'd really like to understand what y'all are talking about over here! ;)
About this post: Hopefully I'm allowed to ask a question regarding a DIY-repair instead of a DIY build... I own a Focusrite ISA One preamp on which the LED level indicators weren't responding correctly. My guess: broken capacitor somewhere, and yes indeed, I found a broken capacitor on the PCB with the led strips.
I decided to take the whole preamp apart to inspect for more faults, and I discovered a few more faulty caps here and there. The unit is purchased new just under four years ago and I think that's quite young for these faulty caps (correct me if I'm wrong)
The brands of caps used by Focusrite are Janicon and L.H. Nova. A google search revealed that Janicon is not a top shelf brand and on L.H. Nova I couldn't find any info regarding quality.
My question: what brand should I replace the broken caps with and might it be wise to just replace all the Janicon and L.H. Nova caps with better grade caps?
I've added some pics some of the pcb's.

Focusrite ISA PCB.jpg
 

soapfoot

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If it were mine and I saw evidence of capacitor failure, I’d probably replace them all.

I’d first consult the schematic (if available) to assess whether the original parts were being run too close to their rated voltage (e.g. 16v rated parts on a 15v rail), which is too often the case and can shorten service life significantly.

If so, I’d see whether I could find a part with a higher voltage rating that had the same lead spacing and would physically fit. For this, it is essential to consult the manufacturers’ data sheets to avoid a lot of trial-and-error.

Try to use quality parts from Nichicon, Panasonic, or any other reliable manufacturer. If you purchase from a larger supplier like Mouser, Newark or Digikey, this will largely take care of itself. If purchasing from eBay or other platforms where the parts are shipped to you directly from overseas, there’s a much higher risk of getting counterfeit parts.

Good luck!
 

dmp

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I don't think the capacitor brand is the best way to filter for quality. Every brand has a wide range of quality. You need to select the high quality product line from the brand. Nichicon has high quality caps, but they've also had notable cap failures in products.

A sufficiently high voltage rating is step 1, as Soapfoot says. i.e. if the power rails are 24v, get at least 35v caps.
Then measure the diameter and lead spacing on the board so you know they will fit.
Finally get a temp rating of 105C or higher and higher hours for lifespan (1000hrs up to 5000 hrs). In Mouser, you can filter with all this criteria.
I often just pick a series that is high quality and get all the caps from the same series, like Panasonic FC, which is also possible in Mouser.
 

rensjepensje

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Thanks guys, this is really helpfull.
The schematics aren't publicly available, so I guess it would be wise to raise the voltage for all caps, just to be sure? ie the busted cap on the LED PCB is a 10uF, 16v 85C cap, I best replace this with a 10uF 25V 105C 1000hrs cap (I found a Panasonic).
Is there a big difference between 2,5 and 2,54 mm spacing?
 

soapfoot

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There's virtually never a disadvantage (and usually a substantial reliability advantage) to going to a higher-voltage-rated part in the same (or similar) package size

As for lead spacing, 0.04mm is extremely small (virtually nonexistent) as a difference. Fortunately we're not building Formula 1 engines here, so as long as you can get the part to fit without too much mechanical stress there's no harm if things aren't exactly the prescribed size.
 

Ivan K.

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Good advice from the other responders. I'd add that I'd up the value by 20-30% or a bit more for lower values like 10uF. I've found that Panasonics usually measure closer to the rated value, but not always. Backing up, the most common tolerance is +/- 20%. Nichicon caps are almost always 15-20% low--cheaper to make! This is especially true on larger values, like 1000uF, and higher voltages.

Since these are not precision parts to begin with, and a decent designer takes this into account, I have found that a higher value than the stock is never a problem--unless it is in a timing circuit, where an electrolytic is mostly the wrong type of cap to use. In a low cost device like the Focusrite, the penny-pinchers also get into the act and insist on cheaper brands of components that often have worse specs and uncertain tolerances.
 

rensjepensje

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Another question, just to be sure.
How do you know the caps are faulty? All I see is some residue from manufacturing.
Well, at least the cap on the led pcb is faulty, it's bloated, a lot of residue and the leds aren't working properly. Also some other caps with residue are in the area of the instrument input, and I am experiencing some hum on the instrument input, so I guess that one would be faulty too (however, I have no idea how these circuits work, I know how to solder and how to replace a cap! :)). Also, the boards are really clean so it seems weird to me that specifically some caps would have residue, also while closely neighboring caps don't and there is no residue whatsoever anywhere else on the board.
 

rensjepensje

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Do the dimensions (LxW) of the caps matter as log as they fit? And is it ok to bend 1,5mm leads to fit 2,5mm? As long as it doesn't prohibit assembly of the preamp?
 

Jon S

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I would fit like for like and size by size.
There are many suppliers out there, RS, Farnell, Mouser to name but a few.
Steer clear of fleabay and amazon!
As this unit is not top shelf either, I would fit Rubycon, RS Pro range, Panasonic etc and tollerance doesn't make much, if any, difference in your case.
If you fit a capacitor with the wrong lead spacing, it will look untidy.
I have been in the service industry for a long time, +55 years and have gained a lot of experience. Don't forget, you cannot buy experience, it comes with time and sometimes, a few mistakes.🔨🪚🧨
 

soapfoot

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Do the dimensions (LxW) of the caps matter as log as they fit? And is it ok to bend 1,5mm leads to fit 2,5mm? As long as it doesn't prohibit assembly of the preamp?
If a larger length/diameter cap will fit without bending, squeezing, or touching neighboring parts I'd personally be happy to fit it if it meant I could increase voltage or temperature rating.

I see no real problem forming 1.5mm lead spacing leads to fit a space vacated by a 2.5mm part except missed opportunity. That's a situation where I'd personally find an up-rated 2.5mm l/s part (if given the chance, I'll always go larger and up-rate the voltage or temperature specs).
 

Ivan K.

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One last item to check. Electrolytics are polarized and must be fitted the "right way round". Check to see if there is a "+"marking on the PCB. Sometimes, the plus pad is square and the minus is round. While Focusrite should be machine inserting all their components, I've seen mis-programmed pick and place machines do nasty things like inserting caps the wrong way. This would explain the bloated cap and residue...or it could be just a faulty cap-but check.
 

johannes

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Another question, just to be sure.

Well, at least the cap on the led pcb is faulty, it's bloated, a lot of residue and the leds aren't working properly. Also some other caps with residue are in the area of the instrument input, and I am experiencing some hum on the instrument input, so I guess that one would be faulty too (however, I have no idea how these circuits work, I know how to solder and how to replace a cap! :)). Also, the boards are really clean so it seems weird to me that specifically some caps would have residue, also while closely neighboring caps don't and there is no residue whatsoever anywhere else on the board.
The pictures don't show the bloat, and the residue is most likely from manual touch up soldering. I don't see how the white stuff on the second picture (reverse side of board) could come from leaking caps since it's on the other side of the board.

My point is, if you haven't measured the cap and found it to be bad, don't jump to conclusions!
 

Whoops

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Would the Panasonic GA-series be a good option?

All Panasonic Electrolytic capacitors, any series, are great and top notch.
I have to this day to see one Panasonic Lytic fail on it's own, never seen it.

I would recommend you to buy any Panasonic rated at 105C and thats it

Like other members said, if you have problems in quite a few Lytic capacitors then I would replace them all, because the others might fail at any point.

I think you should also contact Focusrite and complain about that problem, show them the photos and describe the problem
 
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