Macintosh LC III recap - Capacitor Recommendations?

[gryffinwings]

Hi guys, I'm starting the process of recapping the logic board of my Macintosh LC III, I have enough 10 uF 16V caps, but no 47uF 16V caps or a 100 uF 6V cap, any specific caps recommended for the 47 and 100 uF 16v caps?

I'll be looking to  buy from Mouser as they are pretty close to me.

Thanks for any advice.

 

[Lee Adamson]

When I did my IIci, I was out of SMD electrolytics of the correct values, so I just cut the leads on through-hole electrolytics really short and soldered them to the pads.  It actually worked far better than I expected, and I think I'm going to just leave it that way until they start failing (I used cheapo chinese caps, since I expected it to just be a temporary experiment and wanted to use them up).  I generally prefer Panasonic, and that's what I'll probably use next time, being afraid that I'll just have the same trouble in another 30 years if I use the "correct" SMD electrolytics, but any quality brand Japanese, American, or European capacitors ought to last just fine (and that should apply to SMD capacitors, too).

One thing that I *am* suspicious of is when people replace SMD electrolytics with tantalums.  When electrolytics fail, they fail open, and the circuit is (hopefully) designed with that in mind.  When tantalums fail, they fail *closed*, and again the circuit is (hopefully) designed with that in mind.  But with the recent popularity of recapping with tantalums "because they don't leak", I think we're going to see the magic smoke coming out of a lot of boxen 30 years from now when those tantalums start failing.  Best case it'll keep PSUs from powering up, but worst case it might burn traces on motherboards, which would be really unfortunate.

 

[Fizzbinn]

I recapped my LC III a while back with tantalum caps I got from @trag. I more recently recapped a Color Classic and LC 520 board with tantalum caps I ordered from Mouser:

10µf - 16V - SMT - Size B - Mouser #: 581-TAJB106K016

47µf - 16V - SMT - Size C - Mouser #: 581-TAJC476K016SNJ

100µf - 6.3V - SMT - Size C - Mouser #: 581-TAJC107K006R

Same types are used on the LC III. 

Admittedly I haven’t really thought much about electrolytic vs. tantalum caps so I’ll leave that to others to discuss. 

 

[Oberlehrer]

Electrolytics vs. tantalums: That's an interesting question. I'm planning to recap a SE/30 and a IIsi in the near future and I'm also somewhat torn here.

I've seen tantalums fail in vintage musical instruments occasionally but not regularly.

Macs from the early 90's clearly used both electrolytics and tantalums (as is evident in the aforementioned IIsi); is there a similar failure pattern with those tantalums? I'm not aware of this.

So why did Apple then use both electrolytics and tantalums in that timeframe? The following is a bit of speculation:

As with many other components there was some evolution in the capacitor field. Anyone having recapped musical instruments and amps from the 70's or earlier will have found that replacement caps are almost always physically smaller than the components originally installed. Caps definitely got significantly smaller over time.

I find it possible/plausible that in the early 90's tantalums were larger than their electrolytic counterparts, especially when rated for a higher voltage. I think it took until the late 90's before high capacity tantalums in small sizes became widely available (but I might be wrong about this).

On the other hand tantalums have slightly different electric features (I believe), so perhaps Apple made the choice depending on the circuit?

 

[LaPorta]

Usually, when it comes to this, it was just whatever you can get that is cheapest that will work.

 

[dzog]

I'd be interested in recommendations for high-quality long-lasting electrolytics. I am fortunate enough to have a number of machines with original caps and no (obvious) damage - but can't squander this luck much longer. Ordered a bent SMD tip for my Hakko and have started sourcing some practice boards. (We'll see how it goes...)

If it's true that tantalums are more likely to fail closed than electrolytics, and have some different electrical properties, I feel like I'm better off buying another 20+ years with electrolytics that have an understood failure pattern. 

 

[bibilit]

i have been using tantalums and ceramic capacitors for a long time, never had any issue.

keeping in mind that they won't be used on a daily basis, lifetime is not really an issue.

The biggest problem in our hobby, is not really what kind of capacitor you are going to use, but when you are going to tackle the job.

electrolytics have already being causing a lot of issues in our boards (traces gone...) so the sooner, the better.

 

[bibilit]

i have been using tantalums and ceramic capacitors for a long time, never had any problem

keeping in mind that they won't be used on a daily basis, lifetime is not really an issue.

The biggest problem in our hobby, is not really what kind of capacitor you are going to use, but when you are going to tackle the job.

electrolytics have already being causing a lot of troubles in our boards (traces gone...) so the sooner, the better.