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Don't use 16V SOLID Tantalum on SE/30 Motherboards


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Thank you, my friend! I'll have to let them in on it!

 

I am glad they are: I just used 30 of them on an 8100 and video card, and purchased fifty more!

 

Really, excellent work, and you are a great help to us all who are not so savvy.

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On 3/7/2021 at 12:16 AM, LaPorta said:

...I just used 30 of them on an 8100 and video card, and purchased fifty more!

 

Wow!  That's some serious recapping work you have planned.  

Good luck and best wishes!

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Posted (edited)

@LaPorta I've checked a few sites (digikey, mouser) and looked at the datasheet you posted. As far as I can tell, the Wurth 875105344006 is a solid polymer capacitor and not a hybrid.

 

Edit: Sorry for the ping, apparently my browser decided not to refresh properly and I missed everyone else's responses.

Edited by androda
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On 3/5/2021 at 7:45 PM, JDW said:

 

If you look at the very first page of the IIfx schematic I linked in my previous post, in the upper left corner you find C45 is 470µF 16V.  Such caps would not be Tantalum, regardless of board revision, because the capacitance size is too large for Tantalum. You can find a rare few Tantalums in that size, but even at 1000pc quantities, they are upwards of US$7 each:

https://www.mouser.com/ProductDetail/Vishay-Sprague/597D477X0016H2T?qs=S8ppeYOuFj42wvxjbbwEzw%3D%3D

 

As such, you will typically find Tantalum used for smaller capacitance sizes like 47µF when we are talking about voltage specs of 16V.

 

All said, if you replace an 16V rated electrolytic capacitor on a 12v circuit with a 16V POLYMER Tantalum, you are within manufacturer's guidelines. DO NOT use SOLID Tantalum though.  And make sure the capacitor you choose will fit the pads.  Another good replacement in these cases are solid electrolytic organic polymer OS-CON caps.

 

I think you misunderstood my comment.  

 

What I was saying, without outright saying it, was that the SMD capacitors on the motherboard are either electrolytic or tantalum, or a combination of both on the same logic board.  I was not referring to the through-hole capacitors, like the 470uf you mention.  Only the SMD ones.

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20 hours ago, MrFahrenheit said:

... the SMD capacitors on the motherboard are either electrolytic or tantalum, or a combination of both on the same logic board.  I was not referring to the through-hole capacitors, like the 470uf you mention.  Only the SMD ones.

 

Thank you for the clarification, but my previous advice still applies

 

All said, if you replace an 16V rated electrolytic capacitor on a 12v circuit with a 16V POLYMER Tantalum, you are within manufacturer's guidelines. DO NOT use SOLID Tantalum though.  And make sure the capacitor you choose will fit the pads.  Another good replacement in these cases are solid electrolytic organic polymer OS-CON caps.

 

I lack time to go through the entire schematic and find out which SMD caps are tied to 12V and which are only 5V.  But if a 16V polymer tantalum fits the pads, just use that and then you are covered for both voltages.  

 

The two points I've been trying to make are: (1) voltage rating of tantalum caps matters a lot, and (2) you need to measure to determine if your new cap will physically fit the pads on the circuit board.

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I do appreciate what JDW is doing here - giving people the optimal course of action to preserve their vintage gear. 
 

That being said I think that some perspective of risk is likely relevant as well before people go and start replacing caps because they are worried one might go pop. As was noted earlier on nobody is aware yet of a properly Installed 16v tant cap having shorted in a recapped Mac. Doesn’t mean it couldn’t happen but it’s very low likelihood.  
 

I base that on a couple reasons:

 

1.  From what I read in the earlier threads the 12v occurs as occasional peaks and is not consistent. 
2.  The IBM PC used 16v solid tantalums across 12v  circuits successfully. People do have some of those tantalums pop today but that is 35 years later.  When the machines were in active operation I do not believe shorted Tants were a thing people fretted over. I know for me personally I am fixing these machines up with an expectation of 10 to 15 years. If am not refurbishing for another 30 years as the chances of something more serious impacting the machine is more likely between now and 30 years from now. 

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Actually I see I was incorrect on point #1 in that there are a couple of locations on the SE/30 at least that do see constant 12v but the rest of my feedback stands. You might be getting 25 years out of these caps instead of 40 but still likely no reason to rush to change them. 

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I should say that I am not suggesting you recall all those cap jobs you've done to date and replace your improperly derated tantalum caps.  I think that is going to an extreme.  I am talking about new cap jobs we are planning now.  

 

With that said, while I humbly respect the experienced positions put forth by my fellow vintage Mac lovers, and the design mistakes of the IBM PC notwithstanding, I nevertheless stand firmly behind all I have written in this thread. 

 

I define "consensus" as this: "I've never had a problem, so such-and-such should be perfectly safe."

 

I realize that many folks here are well-versed in recapping and have done things a certain way with issue for years.  I am also aware that most of you read this forum even more religiously than I do, and you are basing your tantalum capacitor safety assessment on the "consensus" of this forum in that few, if anyone, have reported burned tantalum caps many years after a recap.  When we've done a certain thing a lot time, especially if we've not experienced problems, we resist change.

 

But none of that in any way nullifies physics, materials science, or the reality of what tantalum capacitor manufacturer's dictate.  Manufacturers don't just put that derating info into parts data sheets, but also into technical documents describing tantalum capacitor technology in general.  I am not presenting my personal opinion on derating.  I am merely saying we ought to take to heart what the parts manufacturer's say in their guidelines.  Only the can we say, "I've chosen the best caps to recap with."

 

Mission critical systems built by NASA and the US Military, as well as health care products like Pacemakers, which use SOLID tantalum capacitors, often implement an even more strict voltage derating than the 50% derating I have been talking about.  The general advice from tantalum capacitor manufacturer's is a 50% voltage derating for SOLID Tantalum.  That is the rule I choose to abide by for the consumer grade parts I use.  That means if you have a constant 12 volts and you use a SOLID Tantalum there, you need a 25V SOLID Tantalum to be in line with manufacturer's guidelines.  Mission critical applications often take that further and do a 1/3 voltage derating.  So for example on the same 12V line, NASA or the US military might use a 35V rated SOLID Tantalum (three times the working circuit voltage).

 

I should also mention that NASA often gets specially tested Tantalum capacitors which a more resilient against over-voltage than the commercial grade parts we can buy from Mouser, but those NASA parts costs a whole lot more too.  Yet they often derate more than 50% even with those better parts.  To me, that's an important point of consideration when I choose parts for recapping.

 

Next, there is no golden rule that says a 16V SOLID Tantalum used on a 12V line will be fine for its first 20 years of life but then be in the danger zone for the last 20 years, nor is there an absolute life limit of 40 years either.  "Risk Management" is indeed what we are talking about, because a single voltage spike can kill a tantalum within its first year or even its first month of use in a circuit.

 

Why should we even care when so few are even mentioning cases of burned tantalums?  Because SOLID Tantalum, unlike POLYMER Tantalum, fails catastrophically.  It fails short-circuited and burns with an open flame.  I shouldn't need to explain further why that is pretty bad.

 

I cannot tell you how many of my fellow EE's swear they will never use Tantalum at all, in any circuit, because of that fiery failure mode.  I personally think they are going to extremes by committing to that, just like folks who treat the voltage derating flippantly are going to the opposite extreme.  In my mind there is indeed a happy balance.  That balance is strict obedience to the 50% voltage derating for SOLID Tantalum.

 

The good news is that if you just use POLYMER Tantalum, you then can safely use 80% of your capacitor's rated voltage instead of 50%, as per capacitor manufacturer guidelines.  So on the SE/30, for example, you can use a 16V Polymer Tantalum on those CONSTANT 12V lines without worry because 80% of 16V is 12.8V.  If you want derate Polymer Tantalum further by using a 25V part, so long as it physically fits the circuit board pads, there's nothing wrong with that.  I don't think it's absolutely necessary to use 25V Polymer Tantalum in that application, but it's really the choice of the recapper on whether they want to do that or not.  There's no harm in choosing a higher voltage capacitor, so long as it physically fits.

 

It's also important to keep in mind that 12V doesn't necessarily mean 12.00000000V.  In fact, I often measure more than 12V on my compact Macs.  You might see 12.5V. So if you obey the 50% derating rule for SOLID Tantalums, you double the working voltage: 12.5 x 2 = 25V.  For Polymer Tantalum, a 16V part can accommodate a constant 12.5V safely.  That doesn't offer a 100% guarantee that it will never fail, but your odds of catastrophic failure diminish considerably.

 

Lastly, the most dangerous time for SOLID Tantalum caps which haven't been properly derated is at POWER ON.  Flip on the power, and there is opportunity for voltage spikes to hit the cap.  That's most often when they fail.  By using higher voltage rated SOLID Tantalum parts, you considerably lessen the likelihood of failure, which again is a short circuit and a flame.  So when in doubt, just follow the manufacturer's guidelines.  They will not lead you astray.

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Posted (edited)

@JDW I don't think anybody is disagreeing with you that for new recap jobs, it makes sense to go with higher rated parts.  I recapped my IBM 5150 and related expansion cards with all 25V parts a few months ago.  The point I'm making is your thread is alarmist an there are people here worried that they may have made a significant mistake by going with the 16v parts, when chances are, on the balance of probability, I bet they will not see a tantalum failure within the time they are using this equipment.  

 

As a Mac guy, I'm used to recapping everything.  When I was asking about recapping my 5150 after reading about tantalums going pop on the PC forums, everybody (and I mean everybody) said I was crazy to recap.  When they have a tantalum go pop, they just wipe up the char mark and replace.  Now the tants on the 5150 are throughhole which might limit the damage versus an SMD cap on the Mac but I still went ahead and recapped everything (except for my Tandon floppy drive as I didn't have the right caps on hand for that).

 

As per the full article excerpt somebody had posted earlier, the study noted, "It must be remembered that these results were derived from a highly accelerated surge test machine, and ICT failure rates in the low ppm are more likely with the end customer."  And again, those test result failures were driven due to repeatedly applied surge currents - You can't say for sure whether the 12v exposed caps on the SE/30 ever experience any surge conditions in general operation.  Maybe they don't and the 25% derating is fine. 

 

Ultimately you are basing your viewpoint largely on a gut feeling.  And like I mentioned, I don't disagree with the advice of derating.  I personally don't use tantalums as I use solid polymer as I prefer the stock look and I recall that the caps I use have an ESR etc. that is closer to the stock electrolytic.  Ultimately I I just disagree with causing concern for those that have used 16v parts when likely no concern is warranted.

Edited by superjer2000
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The words "more likely" in your quote are key.  As you and I both agree, this topic is about "risk management."  A 50% voltage derating for SOLID Tantalum is industry standard knowledge preached by far more people that just myself.  That industry standard "selection rule" is merely what I am presenting.  You are of the option that my merely stating that fact repeatedly and in specific terms is "alarmist."  And maybe the title of this thread upset you.  I disagree though.  I presented information and explained it in detail, but it is up to the reader of that information to use it or discard it. Someone could just look at this thread and say, "I don't like this thread" and then go on with their life as usual.  Just because I defend universally accepted design rule in accordance with manufacturer's guidelines does not imply I'm over the edge or alarmist.  It just means I take those guidelines more seriously than others.  And when folks have questions, I try to answer them.  That's what this thread has been about.  Really, that is it.

 

Again, you are saying things based on your experience and the experiences of others; which as I said, is all fine and well.  I am merely saying that if indeed you are correct in your assumption that a 16V SOLID Tantalum Capacitor is "perfectly safe for 20+ years" on a constant 12V circuit, then a 25V SOLID Tantalum Capacitor (or 16V or higher POLYMER Tantalum) is safer still AND complies with the 50% derating. This isn't alarmist.  It's just fact.  Picking a higher voltage cap is statistically safer. That is also why I mentioned NASA, the US Military and Medical applications which derate BEYOND 50% even though their have more expensive and superior SOLID Tantalum capacitors.

 

If you've recapped 43 quadrillion circuit boards with SOLID Tantalum that doesn't obey the 50% voltage derating guidelines, great.  I am NOT saying you should recall those 43 quadrillion boards.  That, my friend, would be "alarmist."  :-) 

 

What I have repeatedly said is that FOR FUTURE RECAPPING PROJECTS, let us consider use of voltage ratings that comply with manufacturer's guidelines.  However minute a benefit one wishes to contend that would be, I still say it's sage, factual advice.  That good advice doesn't have the intention of stomping on anyone's toes or slandering anyone's good name in the recapping business.  It's merely manufacturer's guidelines presented in a way the common man can understand.  That's it.

 

Now after my having explained all this, if someone's head is still spinning about Tantalum capacitors, just use OS-CON caps instead.  No voltage derating to worry about.  OS-CON caps also look stock on an SE/30 motherboard too.  And they beat "Hybrid" organic polymer electrolytic caps because OS-CON have a solid electrolyte whereas Hybrids have a fluid electrolyte. (I mention all this in my video, by the way.)

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I just saw this post this morning:

 

 

Have a look at the capacitor at C1.  This is exactly what I observed on my IIfx machine.  Evidence of another blown tantalum capacitor at the exact same location.

 

Can you confirm that this capacitor sees 12v or more on this spot?  I think this now shows actual documented proof of the issue you've been discussing.  Up to now it has been more 'speculation' and 'caution', but it can't just be a random fault if there are now two IIfx with a blown tantalum capacitor in the exact location.  Not to say I didn't believe you before, @JDW, but the counter arguments made it seem less of an issue than it was being made out to be.  This demonstrations the severity of the issue.

 

Edited by MrFahrenheit
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C1 on the IIfx is to HDD power, and as such it has no business being a silly 16V rated SOLID tantalum!

 

Here's the schematic.

 

I'd recommend a 16V or higher rated OS-CON cap there, as they have very low ESR and have no issues with voltage spikes.

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20 hours ago, JDW said:

C1 on the IIfx is to HDD power, and as such it has no business being a silly 16V rated SOLID tantalum!

 

Here's the schematic.

 

I'd recommend a 16V or higher rated OS-CON cap there, as they have very low ESR and have no issues with voltage spikes.

What about using a 35v solid tantalum?

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On 3/11/2021 at 9:50 AM, MrFahrenheit said:

I just saw this post this morning:

 

 

Have a look at the capacitor at C1.  This is exactly what I observed on my IIfx machine.  Evidence of another blown tantalum capacitor at the exact same location.

 

Can you confirm that this capacitor sees 12v or more on this spot?  I think this now shows actual documented proof of the issue you've been discussing.  Up to now it has been more 'speculation' and 'caution', but it can't just be a random fault if there are now two IIfx with a blown tantalum capacitor in the exact location.  Not to say I didn't believe you before, @JDW, but the counter arguments made it seem less of an issue than it was being made out to be.  This demonstrations the severity of the issue.

 

 

@MrFahrenheit  When did your IIfx tantalum cap blow?  I don't think anybody said that it isn't possible, only that it's highly unlikely to occur on a newly recapped board within a timeframe that we'll still be posting on 68kmla to talk about.  The IIfx was discontinued in 1992.  If the cap blew in the last 5 years that's still makes it ~25 years old so I think this is still aligned with what a few folks have said - if you've recapped with 16v tantalums, probably no reason to run out and swap them ASAP, or maybe even ever.  If you're recapping a board now, it makes a ton of sense to use a higher rated part.

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Well, I recapped a Mac IIci for a friend and when he tried it for the first time(albeit few months later), the only thing that came out of it was some smoke and nasty smell. It worked when I recapped it without issues for 8 hours straight, but this was in November.

 

One of the new solid tantalum caps at location C16 (that has +12V across it), decided to short and explode. The PSU is current limited and shut down immediately.

No other damage was done and after the replacement, the machine works like new.

 

Was this a coincidence? Did I apply too much heat when soldering it? Did the cap had a manufacturing defect and even a lower voltage would also kill it? Was there a voltage spike much above 16V? Who knows!

63707973592__2AA8EF11-D59C-4632-9C30-9F01860B19FB.jpeg

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19 hours ago, mitchW said:

Well, I recapped a Mac IIci for a friend and when he tried it for the first time(albeit few months later), the only thing that came out of it was some smoke and nasty smell. It worked when I recapped it without issues for 8 hours straight, but this was in November.

 

One of the new solid tantalum caps at location C16 (that has +12V across it), decided to short and explode. The PSU is current limited and shut down immediately.

No other damage was done and after the replacement, the machine works like new.

 

Was this a coincidence? Did I apply too much heat when soldering it? Did the cap had a manufacturing defect and even a lower voltage would also kill it? Was there a voltage spike much above 16V? Who knows!

 

 

Well now we have at least one potential data point that new 16v tants can go.  You're right, there are a lot of unknowns with regards to the exact cause but this does definitely bolster the argument (opposite of what I was arguing before) that it might be worthwhile to replace the caps where they see 12v. 

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23 hours ago, superjer2000 said:

 

@MrFahrenheit  When did your IIfx tantalum cap blow?  I don't think anybody said that it isn't possible, only that it's highly unlikely to occur on a newly recapped board within a timeframe that we'll still be posting on 68kmla to talk about.  The IIfx was discontinued in 1992.  If the cap blew in the last 5 years that's still makes it ~25 years old so I think this is still aligned with what a few folks have said - if you've recapped with 16v tantalums, probably no reason to run out and swap them ASAP, or maybe even ever.  If you're recapping a board now, it makes a ton of sense to use a higher rated part.

 

@superjer2000 The cap that blew for me was an original.  There are several instances of this location blowing caps that @JDW and I could find just casually looking.  What's interesting is that I would expect a tantalum to easily last 25 years if it were rated correctly.  

 

However, I have heard of people blowing newly soldered on tantalums, and @mitchW is another good example.

 

Perhaps it would be good to determine what 16v stock caps see 10+ volts on all of the various machines and work at creating a list, especially for those who have already done them but want to ensure the machines don't experience a catastrophic failure.  I myself would be willing to desolder any 16v caps where 10v+ is seen (and anywhere that 50% should be maintained).

 

@JDW How would we create a listing for common Mac recaps that should have higher-rated caps for solid tantalum caps?  Where can we find this information ?  

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On 3/12/2021 at 3:40 AM, MrFahrenheit said:

What about using a 35v solid tantalum?

 

On a constant 12V power line, a 35v SOLID Tantalum would be an ideal choice.  But technically, even a 25V SOLID Tantalum would satisfy manufacturers guidelines suggesting a 50% voltage derating.  

 

For recapping projects, where cost is a non-issue, and where the physical size of your replacement tantalum will fit the pads, just as high a voltage will fit.  So if a 35V SOLID Tantalum will fit, use that.  As mentioned earlier, it's about lowering the risk of failure that a voltage spike will trigger a burn-down of the cap.  The higher the voltage of the tantalum cap, the less likely it is to burn.  This is true whether you installed your new cap 1 second ago or 20 years ago.

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On 3/12/2021 at 11:06 AM, MrFahrenheit said:

 

@JDW How would we create a listing for common Mac recaps that should have higher-rated caps for solid tantalum caps?  Where can we find this information ?  

 

It's a matter of either having a schematic which shows the voltage across a given capacitor or actually measuring the voltage across the capacitor yourself. 

 

When recapping old Macs, in most every case you have either 5V or 12V across the capacitor.  That is true if one side is ground and the other side -12V, for example.  12volts is 12Volts.  So if you have 12V across a cap, especially a constant 12V, and especially if that is a power line attached to a motor, such as in a hard drive, you absolutely want to derate your cap in accordance with manufacturer's guidelines of 50%.  Meaning, you need to use a 25V SOLID Tantalum capacitor or better (35V is definitely OK), or use a 16V Polymer Tantalum or better (25V or even 35V) is fine.  

 

Keep in mind that your Polymer Tantalums won't burn down like SOLID Tantalums either.

 

Lastly, I may be an EE, but I am just another voice in the crowd.  Nobody needs to listen only to me on this.  Even the numerous examples of burned down Tantalum capacitors aren't the definitive word.  The definitive word is what the manufactures recommend.  And as I've said countless times, they recommend a 50% voltage derating for SOLID Tantalum.  So all I am doing is just touting factual reality.  That's it in a nutshell.  And of course, by following the guidelines you better insure your Solid Tantalum caps won't burn down 1 day or 25 years hence.  But again, if you can use a Polymer Tantalum cap or an OS-CON, do so.  They won't burn down.

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