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

JDW

Well-known member
The smallest OS-CON capacitor available is 3.3uF, wondering if it could be used here. I really do like to replace with can style caps if possible - I have a perfect main board to recap and want it to look as original as possible.
I would just use a 50V 1uF Tantalum (Solid or Polymer). It’s only one cap so it won’t detract from the stock look if all other replacement caps are OS-CON.

 

JDW

Well-known member
If someone can find data sheets for those sound chips, I would be delighted to have have a copy!  But for now, I am not holding my breath.  The choice of a 1uF was likely deliberate.  Sometimes they are used in timing circuits so you have to be careful.  When it doubt about the purpose of a given capacitor, only swap with the factory capacitance value.

I still think it won't affect the stock look to use just one 1µF tantalum cap; but if you absolutely must have the stock look, then your only recourse would be to use a fluid-filled aluminum electrolytic, which would need to be replaced again 20 years hence.  I found this Rubycon with a 5000h life rating at 105°C, which has the lowest ESR as per the Ripple Current value among other 5000h rated caps.

 
Hi all,

With apologies for resurrecting this older thread - I have just recapped a IIci with 16v solid tantalums, as linked from Bruce Rayne's page at https://recapamac.com.au/macintosh-iici/ . Bruce seems an absolutely upstanding and knowledgeable guy, so whilst I'm not too worried......should I be worried....?!

The machine does get used every few days.

Thanks all
Mark
 

MrFahrenheit

Well-known member
Hi all,

With apologies for resurrecting this older thread - I have just recapped a IIci with 16v solid tantalums, as linked from Bruce Rayne's page at https://recapamac.com.au/macintosh-iici/ . Bruce seems an absolutely upstanding and knowledgeable guy, so whilst I'm not too worried......should I be worried....?!

The machine does get used every few days.

Thanks all
Mark

I can tell you, I have observed factory Apple Tantalum capacitors blowing, and in the same spots on the same models. I have two IIfx machines, one had that cap blown, the other it was going, in the same location). Others here have had the same cap also be blown, which indicates Apple used a 16v capacitor and it really needed a 25v or higher capacitor. So at least on the IIfx board, the capacitor that is connected to SCSI needs to be higher voltage than the stock 16v. There may be others on that model, I'm unsure myself.

With regards to the IIci, it may or may not matter. I am not as knowledgeable with electronics as JDW is. But if the issue happens with the SE/30, and it has happened with the IIfx, then there are definitely going to be at least 1 cap on most Macs that needs to be a higher voltage if a tantalum is used. For now you may be okay, and it may be years, or months, or days, but eventually it may cause more problems than it's worth. If anything, I'd suggest locating the capacitor that is connected to the SCSI power and replacing with a higher voltage one.
 

skab

New member
When I think of tantalum caps, I always think of small little bombs that explode and short out and everybody hates them, so I was a bit irritated when I read about tantalums being the recommended replacement for a classic Mac recapping. What was the actual reasoning for switching to tantalums - honest question, no offence...

What about MLCCs as an alternative? I just ordered another little MLCC (multi layer ceramic capacitor) to replace a failed tantalum cap in a MacBook Pro 2010, which should sort out its "GPU problem" just fine. In this application the MLCC was always first choice as a replacement (for a tantalum, no less), any reason this type of cap wouldn't work in a classic Mac as well? MLCCs are non-polarized and contain no active chemistry at all, so no leaking and no popping ever. Failure mode should be "breaking", which would be a rather benign "fail open" scenario.
 

MrFahrenheit

Well-known member
When I think of tantalum caps, I always think of small little bombs that explode and short out and everybody hates them, so I was a bit irritated when I read about tantalums being the recommended replacement for a classic Mac recapping. What was the actual reasoning for switching to tantalums - honest question, no offence...

What about MLCCs as an alternative? I just ordered another little MLCC (multi layer ceramic capacitor) to replace a failed tantalum cap in a MacBook Pro 2010, which should sort out its "GPU problem" just fine. In this application the MLCC was always first choice as a replacement (for a tantalum, no less), any reason this type of cap wouldn't work in a classic Mac as well? MLCCs are non-polarized and contain no active chemistry at all, so no leaking and no popping ever. Failure mode should be "breaking", which would be a rather benign "fail open" scenario.

I think availability in the various ratings is the issue. Can you buy 47uf 16v MLCC caps ?
 

trag

Well-known member
What was the actual reasoning for switching to tantalums - honest question, no offence...

Several reasons. One is that when we started recognizing the problem, back before 2005 the polymer caps were not commonly available.

Tantalums don't leak. In general, they also don't explode. They were an affordable replacement that was the best optimization available at the time. And at the time the main concern was avoiding a new gooey mess on the logic boards we wanted to preserve. Also, the amount of money in this hobby back then was a lot less. Very few people were going to spend $50 on caps for a motherboard they found in a pile in a drainage ditch.

The analysis that JDW has done is excellent and let's us refine our usage to either a higher voltage to be extra cautious or move to polymers.

We're somewhat hampered in really knowing what are good ratings because we don't know the typical/maximum voltages at the various capacitor sites in Apple's designs. It sounds like there's at least one cap. site on teh IIfx that really needs an uprating on the capacitor voltage.
 

chiptripper

Well-known member
My last buy I ended up grabbing MLCC caps (10uf 16v) because they were cheaper than tantalums. They are a treat to install. Only real issue is finding caps that will fit the pads, most are seriously tiny. Anything larger than 1210 is prohibitively expensive at the moment.
 

Mu0n

Well-known member
JDW - this is hero's work. Very informative of the gritty details of capacitor failure parameters. I regularly teach physics class with too many theoretical concepts in not enough time and sadly, we never reach a point where we have time to discuss real world issues with circuits.

I recapped my own SE/30 in the summer of 2019 and I was also led to believe to mostly take above-spec voltage rating caps, especially for the problematic one (C1?) in the Mac Plus analog board. I did take 19 of these to get extras for my Classic 1, but mostly to recap my logic SE/30 board:


I was rusty at soldering, new at picking exact BOM parts, etc. I'm wondering if my choice is mostly ok. I think so. If I'm understanding correctly what you wrote in your OP, my 20 V can tolerate 16 V (80%) correctly, but that might push things at the edge if I'm unlucky.
 

MrFahrenheit

Well-known member
JDW - this is hero's work. Very informative of the gritty details of capacitor failure parameters. I regularly teach physics class with too many theoretical concepts in not enough time and sadly, we never reach a point where we have time to discuss real world issues with circuits.

I recapped my own SE/30 in the summer of 2019 and I was also led to believe to mostly take above-spec voltage rating caps, especially for the problematic one (C1?) in the Mac Plus analog board. I did take 19 of these to get extras for my Classic 1, but mostly to recap my logic SE/30 board:


I was rusty at soldering, new at picking exact BOM parts, etc. I'm wondering if my choice is mostly ok. I think so. If I'm understanding correctly what you wrote in your OP, my 20 V can tolerate 16 V (80%) correctly, but that might push things at the edge if I'm unlucky.

JDW doesn’t visit or post here anymore.
 

chiptripper

Well-known member
JDW - this is hero's work. Very informative of the gritty details of capacitor failure parameters. I regularly teach physics class with too many theoretical concepts in not enough time and sadly, we never reach a point where we have time to discuss real world issues with circuits.

I recapped my own SE/30 in the summer of 2019 and I was also led to believe to mostly take above-spec voltage rating caps, especially for the problematic one (C1?) in the Mac Plus analog board. I did take 19 of these to get extras for my Classic 1, but mostly to recap my logic SE/30 board:


I was rusty at soldering, new at picking exact BOM parts, etc. I'm wondering if my choice is mostly ok. I think so. If I'm understanding correctly what you wrote in your OP, my 20 V can tolerate 16 V (80%) correctly, but that might push things at the edge if I'm unlucky.
Yes I believe JDW went into self-imposed exile after the great 68kmla crash of summer 2021.

I think you're fine. Not an electrical engineer, but I'd personally feel pretty safe with those tolerances.
 
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