SMD Electrolytic Capacitor: Decoding Capacitance & Voltage Rating

[JDW]

I have an old accelerator board used in the PDS slot of an Apple Macintosh SE/30.  The board was manufactured around 1994.  I want to replace the electrolytic capacitors but I'm not sure how to decode the numbers printed on the caps.  Here's a photo:



As you can see the numbers are:

22
  6A
7C6

I could take guess and assume that 22 means 22uF, but what about the voltage spec?  Would 6A mean 6.3V?  Do any of you know?  There's no logo mark on the cap that I can see to indicate manufacturer.

Capacitor dimensions are:

Diameter = 4.0mm
Height = 5.9mm (including plastic base)

Thank you.

P.S. I posted the photo above using "img" tags wrapped around the URL of my photo, but it displays much too large.  How do I define the dimensions of photos I post?

[T3sl4co1l]

22
  6A
7C6

I could take guess and assume that 22 means 22uF, but what about the voltage spec?  Would 6A mean 6.3V?  Do any of you know?  There's no logo mark on the cap that I can see to indicate manufacturer.

Maybe.  I would guess it's running at 3.3 or 5V, unless it's obviously on a 12V rail.  16V would be pretty safe as a replacement.

It's not a standard code,
https://www.radio-electronics.com/info/data/capacitor/capacitor-markings.php
so who knows.

P.S. I posted the photo above using "img" tags wrapped around the URL of my photo, but it displays much too large.  How do I define the dimensions of photos I post?

1. Well, you can reduce the image itself, by, gosh, about 4x for one this blurry.  It won't display larger than 100% normal size.
1a. I didn't even notice; do you read with a maximized browser?  Man, that's so hard to read, paragraphs the full width of the screen?  I guess you get used to it, but sheesh..
2. add "width=600" or thereabouts to the tag, after img.  Hit quote on this post to see:



Tim

[JDW]

Thanks.  I used my DMM and continuity check to confirm that the (+) side of all the caps in question definitely connect to the 5V rail.  Because of that, I'm fairly certain that "6A" should be interpreted as 6.3V, especially in light of the physical dimensions of the existing capacitors.  So with that in mind I am pondering suitable replacements.

Mouser has drop-in replacement electrolytics for about $0.50 each in 5pc quantities (Panasonic EEE-FP0J220AR).  They are rated at 2000h at 105°C and have a rather low 0.85-ohm ESR.  I thought about tantalum (to avoid future leakage issues), but they are expensive and could go up in flames if you don't voltage spec them at 10V or 16V.  That's why I am seriously pondering 10V 22uF Niobium Oxide replacements (AVX NOJB226M010RWB).  Mouser has them for $0.75 each in 5pc quantities.  They won't burn, have only a 20% voltage derating (versus 50% for tantalum), and a low (but not too low) ESR of 700m-ohms.  The only potential caveat is the small 1210 (3528) package size, which is a mere 3.5mm long.  I've not yet removed a stock cap to see how close the pads are, but if they are close enough for a 3.5mm body then these Niobium caps may be the perfect replacement solution.

[In Vacuo Veritas]

  I want to replace the electrolytic capacitors

...why?

[JDW]

I indirectly explained why in my opening post. Electrolytic capacitors from 1994, due to age, have either dried or have their electrolyte leaking out. This increases the ESR and reduces the effectiveness of the cap. Leaked  electrolyte can also eat through PCB traces over time. That’s why.

[ebastler]

  I want to replace the electrolytic capacitors

...why?

While I am not generally a fan of "preventive recapping", SMD electrolytic capacitors from that period do indeed have a bad reputation. Those used in Apple products of that vintage (e.g. the Mac SE models) are often reported to leak. So it might make sense to replace them all, even if no damage or degradation is visible or measurable yet.

[In Vacuo Veritas]

I indirectly explained why in my opening post. Electrolytic capacitors from 1994, due to age, have either dried or have their electrolyte leaking out. This increases the ESR and reduces the effectiveness of the cap. Leaked  electrolyte can also eat through PCB traces over time. That’s why.

No, this is why you *think* why. Do you *know*?



These electrolytics from 1934 still hold up.

But by all means, recap everything, everywhere, all the time, always.

Hint: Your capacitors are under no stress whatsoever.

[JDW]

That video really doesn’t show much at all. Even I know the very old and very large capacitors for many decades ago still hold up well today. The point is how physically large they are. But in my application were talking about very tiny capacitors with a diameter only about 4 mm. In my many years of experience in working with vintage computers, the capacitors that leak the worst are the very small ones, while the very large ones tend to hold up quite well.  I’m also talking about capacitors made in the 1980s and 1990s, some of which were not designed well with respect to capacitors of old.

So I am not a “you’ve got to replace all the caps all the time“ type of person. But I do have a keen eye to replacing the small caps that are more than 20 years old because I know from experience that they leak the worst.

Furthermore, it’s possible now days to replace these tiny electrolytics with improved technology electrolytic like OSCON or even new solid capacitor technologies like niobium oxide.

Hopefully this will end the debate about why and when we should replace the capacitors and allow this discussion to return due which replacement capacitors might be best. That’s when I personally am focused on right now.

[drussell]

I indirectly explained why in my opening post. Electrolytic capacitors from 1994, due to age, have either dried or have their electrolyte leaking out.

If you actually see any signs of electrolyte leaking out of any of these capacitors, absolutely replace all of them in the device if you want to preserve the device long term into the future.

I've seen many PCBs completely destroyed by those little surface mount capacitors from this era.  This seems especially common when someone puts away some device (working) then a few years later pulls it back out and lo and behold, it doesn't work anymore.  Sometimes by that point it is well beyond repair if there are lots of defective caps all over the place.

This is essentially the same kind of problem as regular zinc carbon or alkaline cells left in devices or NiCd rechargeables on an older motherboard going leaky, etc. etc.  If you don't notice it in time (and it is generally accelerated when left unpowered for long durations) it can be somewhere from a real mess to completely unrepairable by the time you find out. 

Edit: Fixed typo

[TimT]

Capacitors in some Amiga models are also well known to go bad. it's not just because there old, they were poor quality to start with.