My atari 2600 has no sound, which is a common problem with an easy fix, just replace 2 capacitors. The original capacitors are 820pf polystyrene axial capacitors, and these are a bit tricky to find. Could I just replace these with any other kind of capacitor like an electrolytic or ceramic one? DO they do the exact same thing or are they different?
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2\$\begingroup\$ Check the markings again. A 820µF polystyrene cap would be HUGE. More likely it's 820nF or 820pF. \$\endgroup\$– JankaCommented Jul 12, 2017 at 17:47
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\$\begingroup\$ You're right, it's pF not µF, my bad \$\endgroup\$– HenriqueCommented Jul 12, 2017 at 17:51
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1\$\begingroup\$ Is it still a problem then? 820pF polystyrene caps should be available everywhere. You can also use polypropylene caps and any value between 680pF and 2.2nF, I guess. \$\endgroup\$– JankaCommented Jul 12, 2017 at 17:52
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\$\begingroup\$ Really, the ones that kind of look like they're made of glass? No store around me sells them and the people on ebay want 7$ for a capacitor \$\endgroup\$– HenriqueCommented Jul 12, 2017 at 18:04
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4\$\begingroup\$ @Henrique: these 7$ are "audiophile" prices. Polystyrene caps have been replaced by polypropylene caps which are also in general the better choice. They drop in so nicely people sell them as "polystyrene" caps. \$\endgroup\$– JankaCommented Jul 12, 2017 at 18:18
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1 Answer
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Polystyrene caps are no longer made. Their major disadvantage is the low melting point of the film, so they can't be machine soldered, only hand soldered.
Back in the bad old days, they were used when a high tolerance was required. If that was the reason these were polystyrene, then any plastic film capacitor of the tolerance would be suitable.
The main specification advantage of polystyrene is its low dielectric absorption, which only really shows up in professional instrumentation-type sample-and-hold applications. Where this is absolutely necessary, use polyphenylene sulphide (PPS) or PTFE dielectric film capacitors to replace it. Unfortunately, both these types are tricky to come by, and expensive.
Polypropylene film is very nearly as good as those, and much more available.
Polyester film is the standard film capacitor dielectric, widely available and cheap, and still very good performance. It's worth trying this type first, to see whether it does do the job. You can buy these in high tolerance values.
You won't find electrolytic caps that small. Don't use ceramic either.
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\$\begingroup\$ C0G ceramic capacitors are excellent for this application as well. They don't share the bad characteristics like X5R or X7R capacitors. For example the Murata RCE5C1H821J0DBH03A is a fine choice as a through hole part. \$\endgroup\$ Commented Jul 13, 2017 at 8:08
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1\$\begingroup\$ Yes, both NP0 and C0G would be good, but I hesitate to recommend specific ceramic types to somebody who uses electrolytic in the same sentence as polystyrene. They're not as strong for lead attach either if you're trying to replace an axial lead cap. \$\endgroup\$– Neil_UKCommented Jul 13, 2017 at 8:13
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\$\begingroup\$ Polystyrene caps can be found a lot of places, but they may be "new old stock". But for your application polypropylene is at least as good. \$\endgroup\$ Commented Apr 4, 2018 at 18:45