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Can I recap my Classic II with Ceramics instead of Tantalums or Electrolytics?

EmNem543

Active member
I need to recap my Classic II, but when I was looking on Mouser, the Ceramic caps of the same value were a good bit cheaper than the Tantalums and I am wondering if I can use Ceramics in place of the Electrolytics or Tantalums that would usually be there. If I can, assuming they physically fit, is there anything I need to look out for before I order them? I know with Tantalums that you have to check between Solids and Polymers. Is there anything odd about Ceramics?
 

Juror22

Well-known member
I've used ceramic caps (when available) as an alternative for some applications - recapping screens in portables and a few other items. They have the advantage of (generally) smaller size, which helps with tight areas.
 

360alaska

Well-known member
I've done it before, not a problem.

In theory, ceramics aren't as good at ripple rejection due to being non-polar, but it works.
 

EmNem543

Active member
classic_iib_recapping.jpgScreen Shot 2021-11-16 at 1.48.08 PM.png
Will the Capacitors listed here work to replace the capacitors on the Classic II Logic Board? or do I need to adjust some values? I know that they are physically much smaller but I will double-check that later. I just want to know if they will work electrically, as they are far cheaper than going with Tantalums.
 

Siliconinsider

Active member
Ceramic capacitor have a lot of advantage since they are entirely solid, they tend to cost quite a bit more than tantalum and electrolytics, especially when you start to go above 10µF. One trick that I use often is to parallel them (10+10 = 20, close enough to 22µF), which helps you buying less parts.

There are a few things important to know:
- The capacitance is reduced, sometime as much as 50%, as you get close to the maximum operating voltage of the capacitor.
- The thermal characteristic can be important and is indicated by a 3 letter code. Note that your Y5V capacitor is going to have terrible characteristics if you don't operate it at 25°C (+20/-80% of its rated capacitance). X7R is the best class (C0G is only for very small pF values).
On the diagram below, the "K magnitude" is the capacitance variation as a function of operating temperature. As a rule of thumb you'd want to stick with X7R or X5R, and avoid Z5U, Z5V...

Why Z5U and Z5V even exist? they have some advantages, the first one being quite a lot cheaper and appropriate if your device operates at 25°C.

Last, you need to identify what the capacitor is used for. For the vast majority it is used for power decoupling, and the exact value does not really matter all that much as long as you keep the same order of magnitude.

eiaclass2.gif
Temperature-coefficients-of-ceramic-capacitors.png
 
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EmNem543

Active member
Screen Shot 2021-11-16 at 4.54.59 PM.png
I just updated the cart based off of what I understood. Will this work to recap a Macintosh Classic II? The Polymer Tantalums of the same capacitance are very expensive.
Ceramic capacitor have a lot of advantage since they are entirely solid, they tend to cost quite a bit more than tantalum and electrolytics, especially when you start to go above 10µF. One trick that I use often is to parallel them (10+10 = 20, close enough to 22µF), which helps you buying less parts.

There are a few things important to know:
- The capacitance is reduced, sometime as much as 50%, as you get close to the maximum operating voltage of the capacitor.
- The thermal characteristic can be important and is indicated by a 3 letter code. Note that your Y5V capacitor is going to have terrible characteristics if you don't operate it at 25°C (+20/-80% of its rated capacitance). X7R is the best class (C0G is only for very small pF values).
On the diagram below, the "K magnitude" is the capacitance variation as a function of operating temperature. As a rule of thumb you'd want to stick with X7R or X5R, and avoid Z5U, Z5V...

Why Z5U and Z5V even exist? they have some advantages, the first one being quite a lot cheaper and appropriate if your device operates at 25°C.

Last, you need to identify what the capacitor is used for. For the vast majority it is used for power decoupling, and the exact value does not really matter all that much as long as you keep the same order of magnitude.

View attachment 36117
View attachment 36118
 

MrFahrenheit

Well-known member
I'm very curious about this subject. I have been under the impression that you always replace polarized caps with polarized caps, and non-polarized with non-polarized, and never the two shall mix. Or is it a case of "depends upon the use"?
 

Fizzbinn

Well-known member
I'm very curious about this subject. I have been under the impression that you always replace polarized caps with polarized caps, and non-polarized with non-polarized, and never the two shall mix. Or is it a case of "depends upon the use"?
I used non-polarized MLCC ceramic caps when replacing the somewhat odd plastic encased electrolytic capacitors on my Duo 230 LCD panel. They worked just fine in that application.
 

Siliconinsider

Active member
It really does not matter ultimately. Ceramic is usually the preferred choice for high performance applications because they are solid state, long life, and have a very low ESR and ESL. Tantalum and electrolytics are polarised because of their construction, it is a limitation more than it is a feature: The dielectric is formed by an electrochemical reaction on aluminium or tantalum oxide, and this can be reverted with polarity (so the insulation disappear). This is also why you can "reform" old capacitors, by building their dielectric oxide back after long periods of non-use.

The choice of dielectric ultimately depends of the application of the capacitor, but decoupling, in most case, is quite forgiving. your machine will likely work, even if you remove many of the decoupling capacitors. They are hard to model and they are often implemented "by default", or added/removed on a prototype boards to test performance. What matters the most is where they are located on the PCB: close to the power pins of integrated circuits.
Here's a good diagram to "recap" those features :)

Capture d’écran 2021-11-17 à 18.01.53.png

The only reason you'd want to use electroytics is if you need high capacitance values and/or high operating voltages, or if you want to save down on costs as they can be a lot cheaper. If you are not concerned by any of these and are more concerned about performance and longevity you should stay away from electrolytics.

And to finish a couple EEVblog videos about decoupling.



 
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EmNem543

Active member
It really does not matter ultimately. Ceramic is usually the preferred choice for high performance applications because they are solid state, long life, and have a very low ESR and ESL. Tantalum and electrolytics are polarised because of their construction, it is a limitation more than it is a feature: The dielectric is formed by an electrochemical reaction on aluminium or tantalum oxide, and this can be reverted with polarity (so the insulation disappear). This is also why you can "reform" old capacitors, by building their dielectric oxide back after long periods of non-use.

The choice of dielectric ultimately depends of the application of the capacitor, but decoupling, in most case, is quite forgiving. your machine will likely work, even if you remove many of the decoupling capacitors. They are hard to model and they are often implemented "by default", or added/removed on a prototype boards to test performance. What matters the most is where they are located on the PCB: close to the power pins of integrated circuits.
Here's a good diagram to "recap" those features :)

View attachment 36134

The only reason you'd want to use electroytics is if you need high capacitance values and/or high operating voltages, or if you want to save down on costs as they can be a lot cheaper. If you are not concerned by any of these and are more concerned about performance and longevity you should stay away from electrolytics.

And to finish a couple EEVblog videos about decoupling.



I have attached my mouser cart below and I am about to place the order (I just got my Classic II in!). It's a total of 40 caps to recap the logic board and Analog board. totaling about 40$ (including shipping) trying my best to stay away from electrolytics. most of the caps are aluminum polymer or ceramics with the exception of two electrolytics that I couldn't get an alternative for without spending 25$ on a single cap. Is there anything I need to look out for? is 40$USD (Including shipping) for these 40 caps reasonable or should I try to bring that down a bit by substituting some more electrolytics? Any help is apprecieted! I haven't done a project like this one before and I don't want to screw it up. Thank you!
 

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EmNem543

Active member
The Capacitors came in and I replaced the Electrolytics on the logic board with 17 Samsung MLCCs and replaced 23 Electrolytics on the Analog board with Wurth Electrolytic capacitors (couldn't justify the extra cost of solid or polymer capacitors). I had one capacitor on the logic board that I accidentally removed one of the pads of when I removed it, but I was able to solder the new one to the via that the pad connected to and it worked fine.
Before and After of the analog board: (Wurth Caps are Red)
66044300755__DE365186-F6EB-46F8-92C7-9F62E942AA75.JPG66044785174__8312CEA5-A8FB-4CB0-B785-43128BED8FDC.JPG

Some of the MLCCs that I put on the Logic Board in place of the electrolytics (finger for scale):
66043953337__855AEF3B-B951-4C2B-8303-34431693D8AC.JPG
This was my first ReCap and I am not experienced by any means. Any tips, tricks, or insight is appreciated. My soldering skills are not great, so if there is anything that should be redone, or if some more solder should be added somewhere, let me know. (Flux was not cleaned up when this picture was taken)
 

CircuitBored

Well-known member
Any tips, tricks, or insight is appreciated. My soldering skills are not great, so if there is anything that should be redone, or if some more solder should be added somewhere, let me know.

For a first effort this isn't bad at all. I'd actually say it's pretty good. My first attempt at recapping my Classic was an all-out disaster. At the end of the day looks come secondly to functionality. Perfectly uniform and clean solder joints only really earn you bragging rights.

If you want my advice: use more flux and less solder next time. You would be amazed at how little solder you can actually use to attach an SMT cap once you get used to applying flux properly. Did you put solder on the caps before fitting them? I personally don't tin my caps at all before fitting them, I just apply a glob of flux to the cap's pins and make sure the PCB pads are well tinned. Then I put more flux on the freshly-tinned pad and use a well-tinned tip to apply the heat. Good flux will do most of the work for you. There's a knack to making a good contact between both the pad and the component that you can really only learn through practice but having the right soldering tip helps with that enormously.

If you don't have one already, I wholeheartedly recommend getting a "horseshoe" tip for your soldering iron. They look something like this:
8ZcObgu.png

It's basically an oval-shaped flat tip at an angle. When it comes to SMT soldering there is no comparison - any other tip just makes your life harder. Get a nice (high quality) small horseshoe tip and be amazed at how much simpler soldering these old boards becomes. These tips also allow you to do the more advanced techniques such as sweep soldering. On the topic of actual soldering hardware: get yourself a high-quality, temperature-controlled soldering station if you plan to make a habit of reworking logic boards. I don't know what you're currently using but I cannot sing the praises of Hakko's hardware highly enough. The FX-888D seems pricey at first but they last forever and work wonders. My soldering ability improved in leaps and bounds as soon as I stopped trying to hack at things with my AC-powered "dumb" soldering irons.

TL;DR: Nice job! Practice makes perfect. Good tools make a huge difference.
 
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