General Advice

I’ve listed below some general advice that you might find helpful with vintage computer restorations, in case it may be of use to you too.

Electrolytic Capacitor Replacement

Aluminium electrolytic capacitors are commonly used for filtering, smoothing, and decoupling in both high- and low-voltage electronics. They are quite cheap in comparison to their solid-electrolyte counterparts (such as tantalum and polymer electrolytics), so are very common in consumer electronics.

Their useful lifetime is highly dependent on the specific application that they are used in (i.e. frequency, ripple current, steady-state voltage versus rating) and temperature, as well as the manufacturer and series of the specific component. They typically comprise aluminium windings which are coated with a liquid electrolyte, which can dry out over time (negatively affecting the performance of the capacitor, often causing them to fail dead-short), or even leak out and cause corrosion to the PCB and surrounding components.

Electrolytic capacitor leakage in a Microsoft Xbox.

Certain systems are well known for electrolytic capacitor failure, including:

Any system can fall victim to electrolytic capacitor failure, particularly those manufactured during the capacitor plague, so these could be a cause of various issues – however, recapping a system is not a fix-all solution and should only be attempted if you know what you’re doing and have reasonable cause. Instead of “shotgunning” parts at something and potentially making things worse, identify potentially problematic parts by physical inspection and/or using a schematic, and test them out-of-circuit using a capacitor tester such as the Peak ESR70 to give a good indication of their actual health.

There are often several production variants of different systems, each of which may have different electrolytic capacitor values and locations, so take note of which you have. You can also often buy capacitor packs for common systems from sellers such as Console5, but I usually just make up my own by noting the specifications of all of the parts required and ordering a set of high-quality known-brand parts. I only ever use high-quality low-ESR replacement parts, in my opinion if you’re going to the effort to recap something then you should do it properly!

When fitting new electrolytic capacitors, you must take care to ensure that the value, voltage rating, and orientation of the new capacitor are correct – electrolytic capacitors are polarised, so must be installed the correct way around, else they’ll get hot when powered on (and probably explode). The polarity is marked on the case: for aluminium electrolytic capacitors, the negative side is usually shown by a white stripe (for through-hole) or a black bar (for SMD); for tantalum capacitors, the positive side is usually shown by an orange or white bar (for SMD). This catches a lot of people out!

You can’t always trust the orientation markings on the PCB silkscreen (if it even has them, not all boards do), as sometimes mistakes were made in the design from the factory (take the PCB layout of the audio circuit on the Commodore CD32, for example), so care must be taken to match the orientation of the new capacitor with the original. Make sure to take lots of “before” pictures for reference, and double-check throughout.

When substituting electrolytic capacitors, the capacitance needs to be the same, and the voltage rating can be the same or higher (within reason, as typically the higher the voltage rating of a capacitor, the higher its ESR) – when you’re going through all this effort to recap something, be sure to use high-quality replacements.

Where possible, I like to use tantalum or polymer electrolytic capacitors for SMD capacitors and polymer electrolytic capacitors for through-hole capacitors – these are equivalents to standard aluminium electrolytic capacitors but use a solid electrolyte, meaning that they cannot physically leak. It’s common in some systems such as the Game Gear for people to use ceramic capacitors in place of SMD electrolytic capacitors, which don’t have an electrolyte and aren’t polarised – these are microphonic and their capacitance changes with the applied voltage, so they are not appropriate for use in some applications, and I try not to use them as replacement parts where possible.

For SMD capacitors, I usually remove all of them at once using a hot air rework station with kapton tape and aluminium foil to protect the surrounding areas, or by carefully twisting them off using needle-nose pliers (this technique may not be suitable if the pads are damaged, as they could delaminate from the board – and push downwards, don’t pull upwards!). The pads can then be cleaned up using new solder and either desoldering braid or a desoldering station. The board should then be thoroughly cleaned to remove any leaked electrolyte and leftover flux, using 99.9% IPA and an ESD-safe brush.

As for through-hole capacitors, I usually remove each one-by-one using my vacuum desoldering station, then immediately install its replacement part – this minimises the likelihood of getting it wrong. The board should then be thoroughly cleaned to remove any leaked electrolyte and leftover flux, using 99.9% IPA and an ESD-safe brush.

Mains Filter Capacitors

A lot of equipment from the 1980s features RIFA-branded metallised paper mains filter capacitors, including the Acorn BBC Model B, which are known to fail short-circuit and release clouds of acrid smoke during operation. Other equipment, such as the Commodore PET 8032 and 8050 FDD, have mains filter capacitors built into the mains connector before the power switch, which can also fail in a similar quite explosive manner. Mains filter capacitors like this should be identified and removed as part of servicing vintage equipment before attempting power on.