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Has anyone tried replacing the two metal can electrolytic surface mount capacitors on the IIci cache card with tantalum equivalents?

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A question for the hardcore collectors,

 

Does replacing surface mount metal can electrolytic capacitors with surface mount solid state tantalum capacitors harm the collector value of a computer or part of a computer?

 

Fact: Surface mount metal can electrolytic capacitors are prone to leaking their corrosive electrolytic solution onto the circuit board.

Fact: Surface mount metal can electrolytic capacitors are substantially cheaper than solid state surface mount tantalum capacitors.

Fact: Surface mount solid state tantalum capacitors last over 100yrs.

Fact: Surface mount solid state tantalum capacitors cost substantially more than surface mount electrolytic metal can capacitors.

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From my experience, I don't think replacing the capacitors with tantalum negatively affects the value.  Just the opposite.  I found that people are wiling to pay a little extra for a recapped vintage Mac just for the peace of mind.  I mean, they're so easy to replace that if someone really wanted it "all original," you can just as easily remove the tantalums and put on cans.

 

Plus, you're literally talking about pennies for the difference between tantalum and cans.  You're not producing hundreds of thousands of motherboards, so a few cents isn't going to make any difference.  I say go for tantalum, future proof your computer and don't worry about them exploding and leaking all over your motherboard.

Edited by olePigeon

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Facts? You need to do some research. I got old radio equipment from the 1930s that is still running today and those caps are just fine. Yes, the cap's "Frequency" (its Farad rating) and ability to disperse heat while in operation adds or takes away from its longevity. But 100 years? Maybe 50 years, definitely 20. Tantalum caps are great but they have been known to fail. Once you have them in place and the system restored and running again, they might out last you.

 

Tantalum Caps are not expensive. And if you want solid state caps, today's SMD/SMT Ceramic caps are just as great and a lot cheaper. If you want looks - get the Black Tantalum Caps - because black Tantalums is what Apple uses on the few board they made with Tantalum Caps (the IIfx and Q950 I have has Black Tantalum Caps). There are a few boards with yellow caps, but Black caps in my opinion is more attractive. They say "I belong here." If you think the Yellow Tantalum caps are expensive, you wont be able to afford the Black ones. But really, it's 75¢ compared to $1.20.

 

If you are going to replace the caps on cache card, either Ceramics (so they look like the others on the board) or Tantalums - in my opinion - Black Tantalum.

 

Know what you are getting. Buying in bulk (more than 10 in some cases) the price drops, sometimes by half. So "Expensive Tantalums" tend to cheap Tantalums. And SMT/SMD Ceramics being the cheapest of all can go as low as 10¢ in bulk. The difference is the output of the frequency - Tantalums (and Electrolytics) tend to be more square in their signal and Ceramics being more sloped or trapezoid in theirs. But they are there to filter the square wave of the PSU into a constant output so it is constant through out the logic board.

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Facts? You need to do some research.

/

the cap's "Frequency" (its Farad rating)

 

I just...

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I'll say this ONCE: To my understanding, the Farad rating doesn't represent a capacitor's "frequency", but rather, its "storage capacity". A cap with a higher farad rating can store more energy (hence, why very large caps can give a potentially fatal shock when handled improperly), so they're sort of like small, relatively low-capacity batteries in that sense. Although, caps do have interesting frequency-related properties.

 

To that end, here's a reputable-looking article that explains everything you'd ever need to know about capacitors.

 

c

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There is a lot more to Farad rating than just "Frequencies" of a capacitor; it is 2 metal plates with a piece of dielectric material in between them. One of the plates is connected to the - side of a circuit, the other side to the + side and one plate gets negative charged and the other side positively charged. How fast that happens depends on the size, shape and area of the plates take up and at what point the dielectric material gives in to the difference in charges between the two plates and "BAM!" an electrical pulse goes through the negative plate to the positive plate. How often this happens a minute or a second is its farad rating. This is why many would call this the "frequency of a capacitor" as its farad rating.

 

Now this was a lecture I did not want to put down as I am retired from teaching and no one here is paying me $35/hr for lessons in electronics. So I'm just stating that under this "frequency" or Farad rating; how long that cap is going to live depending on many other factors like age, heat, voltage/over-voltage/under-voltage, failure of materials, and so on.

 

The problem that plagues Macs is the Leaky Caps where the rubber seal fails at the bottom on those 47µf and 10µf capacitors rated for 16V, and the Cap Goo oozes out onto the board and traces get eaten away. Other Caps in Macs (and other systems) fails too but these two are notorious in failing in every system that has them in 10 to 25 years - depending on usage. Even putting a Mac on a shelf as a display unit and it is never turned on, these caps will fail anyways, it will just take longer to do so.

 

Now some caps have been known to last since the 1930s with old radio equipment still in operation today. Some need work and caps in some cases needs to be replaced, but at the rate caps fail in a Mac, if the Mac was from 1930 - Pre WWII, they would need service of recapping before the start of the Korean War! So there is a lot of factors as to how long a cap would last.

 

A Ceramic or Tantalum Cap should last a minimum of 20 years; unless the Mac is hit with a Power Surge and caps get toasty. But lets say 20 years. Given an average age of a 68KMLA member being in the mid 30s, that means that by the time the member hits his/her mid 50s in 2036, caps in the Macs should begin failing. Personally, I'll be in my 70s by then, but I would will continue long after that! HA! So Macs being recapped today should in theory last until 2036. Other things can go wrong and they need to be fixed as well. That's a given. But if done right, who knows - Old Macs In Space? That would nice to see.

 

And on the IIci Cache card, there are only 2 caps to worry about. Just 2.

Edited by Elfen

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I'll say this ONCE: To my understanding, the Farad rating doesn't represent a capacitor's "frequency", but rather, its "storage capacity". A cap with a higher farad rating can store more energy (hence, why very large caps can give a potentially fatal shock when handled improperly),...

 

On my workbench I have a 1.5F(arad) cap rated for 2.5KV (from my Gas Laser Days). Damn thing is a monster of a cap! You want to talk about storage capacity? If charged up I can put it to someone's chest and blow out their heart with damn thing! What you're stating in theory the caps on a Mac Logic Board can store an infinite amount of power. And that's not true. The caps on the logic board are rated for 16V. When some of us recap, we put higher rated caps so it can handle power surges better (I use 20V caps when I recap). But I seen on sale at ham fests 1.5F and 2.0F mini "Super" caps rated for 5V, they about the size of a 1/2 AA PRAM Battery, and they are great for acting as a PRAM Battery for a system. But they are also expensive. These caps wont kill you if mishandled. My Monster cap on the other hand.... Shit... And I have other dangerous caps in the house - again from my Gas Laser days.

 

A "tiny" .33F @ 1.2KV cap I had for a large Xeon Strobe for a crystal pulse laser, I was swapping out the Xeon Bulb from the unit and I thought it was discharged. It was, but it began to recharge a bit before I unplugged it. So when I grabbed one of the legs of the Xeon Bulb (the middle Ionizing pin) with a pair of plies and my hand slipped, hitting ground - YEOW!!!!!! It felt like my hand was blown right off my wrist with a stick of dynamite! It took 20 minutes to regain feeling back into that hand. I swear! And I've been shocked by the B/W 9in analog board many times before, but nothing was like what this Xeon Strobe did!

Edited by Elfen

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Dude, just stop.  F for farad has zeero to do with "frequency".  Please stop pulling "facts" out of thin air and doubling down when people notice.

 

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I wonder if he is confusing Farads with ESR?

 

there are certain caps rated for special purposes and frequencies... for example in some CRT circuits there are special high frequency caps that look like they are waaayyyy too large for the ratings because of the frequency the circuit operates them at... replace it with a "regular" cap and fireworks ensue!

 

as frequency goes up resistance will start approaching zero...

 

there is a nice online calculator for this

 

http://www.meraman.com/htmls/en/XcCalc.html

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no no I agree Farads != frequency but frequency has an effect on the effective farads of a given capacitor in circuit

Edited by flecom

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Whatever you do, RECAP THIS CARD.

 

I had a cap blow on one of these. It fried the card, plus my IIci smelled like burnt fish for a good while (as did the entire room).

 

It came as a huge shock to me, too, since I had just had that IIci's logic board re-capped a year earlier. I'm running a cache card-less Iici for the time being, but for educational games, it really doesn't seem to make a difference. 

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The relationship between frequency and capacitance is that the impedance of a capacitor is 1/j(omega), where omega is the frequency of the voltage. At 0 frequency (DC), the impedance of an ideal capacitor is infinite. In other words, a capacitor is an open circuit in a DC circuit, but shows reducing impedance (resistance) as the frequency increases.

 

Hence, a capacitor in series acts as a high pass filter (allows high frequency signals to pass), and if you put a capacitor in parallel it will short out higher frequencies, thus acting as a low pass filter; only low frequencies are allowed to pass.

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The relationship between frequency and capacitance is that the impedance of a capacitor is 1/j(omega)

Should have been a C in the denominator of that equation, to make it clear how capacitance and impedance and frequency do have a relationship.

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