Capacitor Replacement on a Commodore 64 - A Lesson in Through-Hole Soldering -- Workbench Wednesdays 04

Concerns about bending the polymer's leads came up in the YouTube comments. Here's a detailed response with pictures.

by spreading the capacitor leads wide like that will stress the rubber seal and it will leak years sooner than a buying a proper axial capacitor that fits there.

The capacitors used are polymer aluminum. These are a solid device with no electrolyte (or other liquid) to leak out.

Here is the construction diagram for the A750, one of the capacitors used.

It even goes to the extent to make sure users realize the polymer layer is solid, not liquid. If you open the KEMET A750 family datasheet in Acrobat, there is also a 3D model on the first page. I did make a mistake in my original YT reply when I said there was no seal. In fact, polymers DO use a rubber seal, but for the opposite reason, that traditional wet-electrolytics do. With a conventional electrolytic, the goal is to keep moisture inside of the can while still allowing hydrogen gas that builds up from the dielectric regrowing, to escape. In the case of aluminum polymers, the seal is there to keep moisture OUT. The polymer material is PEDOT which is hygroscopic. When it comes in contact with moisture, it oxidizes. That oxidation increases the polymer layer's ESR (and affects the lifetime of the capacitor.)

Second did you compare the ripple current specifications of the old caps?

The ESR of the new caps are orders of magnitude less than traditional electrolytics. Which means, they have orders of magnitude more ripple current carrying capability. The polymer aluminum capacitors here have ESRs in the range of 18 milliohms. In terms of rated ripple current, the A750 polymer can handle 3 Amps, while a modern traditional wet-style of the same CV only has a ripple capability of 85 mA! Absolutely no reason for concern there.

I've used them before, and polymer caps are wrapped just like a regular electrolytic cap.

Canned capacitors are wound, not wrapped.

But if they have a solid core then they are surrounded with a electrolytic liquid. 

That is incorrect. There are two types of polymer aluminum cans. Solid and Hybrid. The most popular are solid. (Hybrid is only available from one vendor.) In solid polymer aluminum can caps, there is no liquid.

The hybrid varient does, however, include both the polymer and an electrolyte. That construction allows more of the dielectric layer to come in contact with the cathode foil through the added electrolyte, which increases effective capacitance. The additional ions available on the electrolyte also allow for the dielectric to re-grown when exposed to higher voltages. However, hybrids have a cost premium over solids.

Only ceramic caps are a solid material without an electrolytic liquid. 

Again, this is incorrect. I've already pointed out multiple times that polymer aluminum cans are solid. Additionally, tantalum-MnO2, tantalum-polymer, niobium-MnO2, niobium-polymer, film (PEN, PET, PPS, PP), and aluminum polymer chip capacitors are all solid capacitors with no electrolyte. (There are, however, variants which may include one. For example, tantalum slugs in a rhobidum-based electrolyte for high-temperature applications.)

What caps did you use, I would like to look them up.

They are included in the show notes, which was available in the description link (and the table above.) Additionally, I strongly recommend watching my video The Learning Circuit 40: Learning About Polymer Capacitors. You might also find these articles I wrote in my previous career helpful.

1. How can material selection improve capacitor reliability.

2. Self-healing capacitors can fix themselves.

Using the right tool always makes the job easier.

You did a good job pointing out the maintenance issues with de-soldering tools. This issues is often over looked and can cause many problems. Tool maintenance is important, do it after every use.

DAB