I remember when my parents bought their first TV set. It was in 1950. Vacuum tubes were pretty much the state of the art. Then the sixties rolled around. Solid state devices were the state of the art.
During the 1970's the first microprocessor appeared on the market. It was a four bit microprocessor. Today, we hear about 64 bit microprocessors. Back then, each memory chip had about 1 kilobyte of memory. Today, we have memory sticks that hold gigabytes of memory.
Prior to the microprocessor, programming was done with diodes. It is amazing how electronics has advanced. was applaud their desire to learn.
But despite all the advances, the safety issues remain the same. One act without thinking can cause serious injury or death. Every once in a while, a news report tells of a tragedy wherein somebody tinkering with electricity is accidentally electrocuted.
Years ago, I heard my supervisor warn a technician about high voltage within an instrument. Next thing I knew, the technician was thrown backwards. The chair fell to the ground and the technician was slammed into the wall. He was lucky. He did not need medical attention.
The golden rule is always be aware of what is within your reach when repairing any electrical equipment. Back in the days when plugs were not polarized, a person was working with two instruments that were isolated from ground. Both instruments had metal chassis. He did not realize that 110 AC volts existed between the two chassis. This was because one chassis was connected to common via its power plug while the other chassis was connected to 110 AC volts via its power plug.
If a bare wire that is connected to 110 volts AC comes too close to the common terminal, there may be arcing which will eventually heat up the wire enough to melt the insulation and possibly cause a fire.
Make sure your connections are solid and can't be undone via pulling on the wire. Inspect all your solder joints with a 3x magnifying glass to ensure ensure that none of the solder joints are cold.
Always be acutely aware of where high voltage exists within an instrument; Especially because if your hand gets too close to a high voltage contact, the high voltage may reach for you.
Don't assume that dangerous voltages do not exist in an instrument that is not powered up. A great example of this is the high voltage on the cathode ray tube of an old oscilloscope. Back in the early 1970's, thousands of volts were applied near the front of the tube. Some of that voltage still existed after the instrument power is removed. The old TV picture tube also had thousands of volts at the anode of the tube.
Isolation power plugs are appropriate in some situations. However using a isolation plug on a instrument wherein chassis is suppose to be grounded could cause problems.
Let's talk about troubleshooting an electronic circuit. The troubleshooter should be aware of the implicit assumptions made via his first attempts to resolve the problem. For example; if the troubleshooter views wave forms at various components in the circuit, the troubleshooter is implicitly assuming that the power supplies within that equipment are okay.
Always check for the obvious first. If you are troubleshooting an audio system, check the external cable and power cord connections first. If the instrument does not turn on, one might want to try switching power cords. Check the connectors too. For example, the old RJ-45 connectors might fail after being connected and disconnected numerous times. A USB socket may need a cleaning. A cable may have a broken connection at one the pins in it's connector. In the connectors, I use to work with, the pins were replaceable. I found cases wherein an edge connector on a printed circuit was at fault.
Sometimes I would start troubleshooting by measuring the power supply output voltages and the potential on the common and ground clads. In one case, I measured a half volt from one end of a ground clad to the other end. I found a very fine crack in the clad by using a magnifying glass.
One unusual problem I heard about was a broken lead on a transistor that was not noticed during initial inspection. When the person went to unsolder the transistor from the board, he found that one had disconnected from the bottom of the transistor.
It is always good to understand how an circuit works before trying to fix it. If a schematic is note available in the user's manual, one can always do an online search for it.
Let's consider a problem wherein the symptoms of the problem are changing. How does one troubleshoot this circuit? If one tracks down one symptom and the symptom changes while attempting to find its source, time has been wasted. The answer is to figure out why the symptoms are changing. It may be a bad connection that keeps making and breaking.
How about a problem wherein noise is on the power lines and the signal lines within a weighing scale? Then one has to figure out where the noise is originating. Does the noise consist of a bunch of transients? If so, do the transients coincide with the rising and falling edge of a pulsing signal? If the noise airborne? Is it coming from a drill or a motor nearby? Are there any external cables connected to the weighing scale? Do the cables come too close to a cable from some other equipment? Could the noise be coming from a walkie talkie? Or could some device be transmitting a very strong signal that the weighing scale cannot filter out?
Remember that any appliance containing a motor can be generating electrical noise. This includes a vacuum cleaner, an electric drill, etc.
Think of the simplest solutions first. If a monitor is not working, check if it is plugged in. Check if the fuses good. Do all the obvious checks first because those checks can save one a lot of time.
Good Luck!
