NJRoadfan wrote:If cost isn't a concern, modern multilayer ceramic and polymer capacitors can be used in many of these circuits without a problem.
https://68kmla.org/forums/index.php?/topic/19 … rs-mlcc-smdsmt/
Modern motherboards have long switched away from wet electrolytic to polymers.
Yes, and it would be easy to recap older mobos with polymers as the uFs are relatively low compared to some of the heftier pentium 4 boards.
lissajous wrote:Some tantalum capacitors might become volatile with age but this certainly isn't guaranteed. I will take the fact that the ones […]
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Some tantalum capacitors might become volatile with age but this certainly isn't guaranteed. I will take the fact that the ones in your computer still looked to be in good condition despite being several decades old as a good sign.
They definitely don't look like wet slug tantalums. All of the ones I've seen used sealed cans, like aluminium electrolytic capacitors.
Ceramic capacitors are a better choice than film capacitors for decoupling at high frequencies, i.e. the kind of frequencies you see in computers. These sort of capacitors would be my first choice for this application since they are now available in high values which are physically small and inexpensive.
You need to differentiate between power supply decoupling and signal decoupling. I wouldn't use a tantalum for signal decoupling in an analogue circuit either, but they work very well at power supply decoupling.
It's much more likely that this is a manufacturing error than a design error.
But aluminium electrolytic capacitors also have a oxide layer which can fail.
You would use a film capacitor for power supply decoupling in a digital circuit? That doesn't make sense.
I am referring to using the films as audio decoupling-- or in general areas to replace pF tantalums. Or as I already stated, VCO tuning caps. I am not sure how you are confusing the use of decoupling with power supplies and audio, it was just a quick explanation between the two.
--> and there are specialized film power supply capacitors... so I am a bit perplexed why you are making an argument on a superficial point when I provided quite a lot of information on why vintage capacitors need to be replaced.
And yes films have been around for a long time-- and as I stated secondly-- they were too expensive for most consumer products, hence cheaper and inferior counterparts like ceramics which ARE NOT GOOD for VCO stability, and cause mechanical feedback!
Despite being decades old??? I replaced *all* of the capacitors in the system regardless of type.
Ceramic capacitors act as pickups and are not suitable for synthesizers. As for motherboards, you'd have to but nuts to put them in-- as most motherboards don't use pF. It would introduce noise over time on the bus, as well.
The design was not a manufacturing error, but a schematic error. IBM placed incorrect polarity marking on the silk-screening-- and the manufacturing assembled them according to [that] silkscreen error.
Aluminum capacitors do not use a tantalum oxide layer, which is what I was getting at.