Repairing electronics without killing anyone 2: … unless you know what you are doing.

This is the second part on my series “Repairing electronics without killing anyone” (REWKA, part one is here). In this article I would like to address the ominous phrase “unless you know what you are doing”. So far, I have never heard someone tell me “Now you know enough for doing this”, even when getting a certification, you need to learn the intricate details by applying your knowledge. In contrast, I’ve heard and read hundreds of times the phrase in the title. Many youtube videos showing stuff with somewhat higher voltages (mains voltage) include this phrase in the introduction.

Why is this phrase used so often

There are different reasons, why someone might tell you this.

Many people showing something potentially dangerous just want to not be held responsible for something they show (CYA). If there is any legal justification in doing so depends hugely on your local legal situation.

Another reason is, that these people are aware that they are doing something dangerous. By telling you about this, you do not get tempted to repeat this if you really “do not know enough”. Be aware: Some (very bad) youtubers show stuff with electricity which is life threatening and have no notice or only a do not touch notice, even though you should never do what they do.

Then there are the people (which can have the motivations mentioned above), that themselves “do not know enough” and show something dangerous. Being aware of their lack of knowledge, they want to warn you to not repeat what they do. There are many “repair” channels in which usually safe devices are repaired (e.g., game consoles) and from time to time they try to fix something in the mains voltage part. During these repairs often something somewhat bad happens. Whether they show their failures in the video is out of honesty or just for show remains open.

And finally, there are the professionals who just want to show one aspect of a repair or construction and do not intent to explain everything they do to stay safe. This often makes sense, because explaining all the safety aspects would take more time than showing what they want to show.

The problem

It is very hard to know if you know “enough”. It is even harder (impossible?) to write it down in one place. Simple checklists (as I try to create one below) can never cover everything involved. Apart from the basic knowledge, there is always the proper understanding of the device you want to repair.

Nevertheless: an attempt

In the following I will try to define some “levels” of knowledge, what they contain, and what you can do with these levels. This is purely based on my experience and not on some research, so take it with a huge grain of salt.

As I said before this list is certainly incomplete and should only give you a rough set of keywords. Before doing anything, turn on your brain, read up on the stuff you want to do and be cautious!

Level 0: replace identical, easily accessible parts

If you just start with repairing stuff, you probably do not know a lot about electricity and devices. This is no problem for a first set of repairs.

You can, without danger, replace parts that are meant to be replaced by users.

Many manuals list the parts that can be replaced easily.

Knowledge: buy exactly what is written on the part/in the manual, if not, ask someone to help you whether a part fits

Examples: Light bulbs, power tool battery, vacuum filter, add RAM to your computer

Level 1: open and repair devices with voltages below 40V

The next level is when you start opening stuff which is not trivially accessible. Many manufacturers today think that you should not access these parts of the device (they are wrong!). There are many things that can be done on such devices to prolong the devices’ life.

Knowledge: know how to see if a device runs below 40V, be aware of big capacitors, fuses

Examples: connect torn cables, replace (non-replaceable) batteries, exchange a PCB, replace internal fuses

Level 2: off-line repair mains powered devices

If you want to repair mains powered devices, you need to know some more things. The most important thing on this level is to never do anything on an open device under power. Ideally you always properly close the device for any test.

If the device is open in front of you, you always have to be sure that it’s unplugged.

Knowledge: fuses, thermofuses, insulation, really be aware of big capacitors, proper cable connections, verification of device safety, component voltage ratings, RCD protection,

Examples: replace a thermistor in a rice cooker, replace motor on a power drill, replace the control bord to your flat iron

Level 3: on-line repair mains powered devices

This is where it gets really dangerous.

Working on a device which is open, and mains powered can be life threatening (and often not necessary for repair). You are one slip away from getting shocked. This situation can also occur if you (only) want to work on a low voltage part of a device which has mains powered parts (e.g., the control circuit of a dehumidifier) and you power it up when open. It happens quickly that you brush over a part with mains voltage when measuring something somewhere else.

Knowledge: safety ratings/categories, how to measure higher voltages, self-protection protocols, isolation transformers, personal protection equipment, understand circuit layout, understand measuring device limits/behavior

Examples: diagnose power supply, troubleshoot motor driver

Level 4+: higher voltages than main or safety critical devices

This is the level when someone really told you, that you know enough for what you want to do. Don’t even try it, leave that to the pros (the ones who really know what they do).

Higher voltages can easily kill you to death. If you badly fix a safety critical device, you can kill people that use the device.

Knowledge: professional education, certification of the necessary skill

Examples: Microwave, Medical devices, vehicle break-electronics

Conclusion

With this article, I tried to do what I said was impossible. These lists should give you a starting point and some orientation. If you think that you want to tackle the next level, carefully read up on the knowledge I listed and probably on all the references about this stuff as well. I will explain many of the things I mentioned above but it will take some time.

If you think you know enough (see?), still be very cautious when applying your knowledge!