No, but this is typical of comments people find online.

I’ll preface this by noting that the details are nuanced as with all technical concepts. Knowledge and experience play a huge part in unlocking this and one cannot expect to know much about a topic after just a few hours of reading. Deep learning takes years and is ongoing.

Just as most people lack the experience and knowledge to rebuild their car’s engine or diagnose human illnesses, most DIY attempts to replace electronic parts in complex equipment that likely measure within spec are a recipe for trouble.

It is critically important to note that DIY repair attempts are generally unlikely to resolve faults while dramatically increasing the risk of damage, introduction of additional faults and electrocution.

Dunning-Kruger

The Dunning-Kruger effect occurs when people over-rate their level of understanding of topics they understand little about, yielding the classic “A little knowledge is a dangerous thing”, the Darwin Awards, etc.

A classic case is this Hollywood actor who read a few books and now thinks he knows better than the world’s greatest mathematicians and physicists. A much less extreme example concerns capacitors, a generally poorly understood topic, and a reader’s comment on an article I wrote about the wonderful Kenwood KD-500 turntable. Let’s examine this and advance some factual information in place of opinion.

We need to be critical of sources and understand that too much time in the wrong places can prevent legitimate learning through missed opportunities and the need to then unlearn nonsense later.

Capacitors

Here’s the comment, about speed issues with a turntable, unrelated to capacitors:

A simple fix can be changing any electrolytic caps.. Always good to remove then and check there [sic] capacitance. 10% below should be changed.

Mark, commenting on one of my KD-500 articles

Like so many armchair diagnoses and observations, Mark’s statement is incorrect, has no relevance to the device in question which he has not examined, and will not help the original commenter fix his turntable, so I replied as follows:

Thanks for your comment, Mark. I appreciate those trying to assist others, but given that your comment highlights general misinformation regarding technical electronics repair and only encourages capacitor replacement rather than finding and fixing the issues, it’s helpful if I explain why.

Capacitors are much maligned and generally poorly understood. Capacitors should be checked, but rarely cause speed issues with these decks. New caps are typically specified to be within +/- 20% of rated capacitance, like these excellent Panasonic parts for example https://industrial.panasonic.com/cdbs/www-data/pdf/RDF0000/ABA0000C1209.pdf.

A reading of within +/- 20% is within new part specs and measurement error. Replacing capacitors that measure within 10% of spec is not only a waste of time and money, but it will not fix anything unless those parts also have a measurably very high ESR.

Most end-users also don’t have the test equipment needed to make these measurements accurately, or the experience to interpret the results and therefore should definitely not remove or change parts they cannot properly measure and assess.

Liquid Mike

Did You Know..?

Did you know that brand-new capacitors typically measure low for C and high for ESR? There’s nothing wrong with them, they need to reform, the process that happens when they are first charged. According to the commenter’s theory, even brand-new capacitors that have sat for a while should be thrown away. This is, of course, incorrect.

Capacitors can fail and must be replaced when they do. They can also be replaced to significantly improve performance, depending on their role in a circuit. However, a 10% variance from rated spec does not constitute failure and may be within the measurement error of the typically ordinary test gear most owners will have access to.

TLDR

All too often, DIYers and unskilled technicians bin perfectly good parts and replace them with inferior parts, trying to solve problems that are not even caused by bad capacitors. ESR is a more important parameter than C in terms of capacitor health. Proper lab-grade test and measurement equipment is needed to properly test capacitor parameters, equipment most people do not own.

Replacing parts can cause circuit board damage and introduce new faults. This is especially for those working with cheap soldering and re-work tools, ie people who probably shouldn’t be doing the work. Again, glancing through the Hall of Shame provides ample examples of this flawed approach.