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I have a recording desk which uses a 12 VDC, 4 A power supply. I always turn off the desk after use, but have not turned off the supply (220 Vac) to said power supply for maybe 7 or 8 years. The whole caboodle is perhaps 20 years old, Boss.

Lately, the desk has been turning itself off and back on again. I reason that it's either the desk going faulty, or the PSU wearing out. No other options, really.

Is that a phenomenon of power supplies, when left 'working' for long periods of time, will go faulty?

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    \$\begingroup\$ 1) How warm is the PSU? 2) Could the wires too it be a bit damaged? For example, if they are stretched or frequently bent then the copper inside can be broken and make an intermittent connection. \$\endgroup\$
    – Andrew Morton
    Commented Jul 14 at 13:54
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    \$\begingroup\$ @MarcusMüller - well aware of that, but it and its wiring haven't moved an inch in all that time, so no punctures, I believe! \$\endgroup\$
    – Tim
    Commented Jul 14 at 13:58
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    \$\begingroup\$ @MarcusMüller I've had a tube on an old bicycle fail because it was embrittled with age. \$\endgroup\$
    – John Doty
    Commented Jul 14 at 14:31
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    \$\begingroup\$ It's possible that it has. It's also possible that it hasn't. It is possible to hook an oscilloscope to the power supply rail (if you know what you're doing) and test for voltage ripple and brownouts. Justme mentioned electrolytic capacitors - those are a type of part that wears out sooner than most parts. \$\endgroup\$
    – user20574
    Commented Jul 14 at 15:04
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    \$\begingroup\$ One of the main failure mechanisms for a lot of electronic equipment is the power surge when it's switched on. This applies for everything from light bulbs to computers. Often the stresses are at their greatest for the first few mains cycles as filaments heat up, smoothing capacitors charge up etc (it's often called "inrush current"). You say that you switch the deck off, but leave it's power supply permanently powered, so the output of the power supply would be subjected to said inrush current every time you use the desk. So yes, it could have worn out. \$\endgroup\$
    – Peter Jennings
    Commented Jul 14 at 16:14

2 Answers 2

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Essentially all electronics have a limited lifetime. The manufacturer specifies conditions for use of the electronics – for power supplies, these are, for example, input voltage (and frequency of AC etc.), maximum output (load) current etc. and also generic parameters of the environment such as minimum and maximum temperature, humidity and so on.

The same applies to each component in the device.

Conditions causing damage

Mechanical wear and tear

Wires can be subject to pulling when the device is manipulated. They can also become broken by frequent or significant bending, mechanically loading them and so on. This is quite easy to notice on wires that are outside the device, but this also applies to wires and other connections inside the device.

Long time loading of the enclosure of the device can also cause components, especially the printed-circuit board to bend and eventually develop cracks.

Vibrations and mechanical shock can cause a lot of bending. This applies to everything: enclosure of the device, wires (even inside it), and importantly the components. Through-hole components such as coils, capacitors, …, especially these mounted on two or three “legs” are quite vulnerable to vibrations, unless they are properly mounted. When the device is vibrating on specific frequencies, you can see the components literally flapping.

To make components less vulnerable to vibrations, a blob of epoxide or a glue is used to cover the components and hold them fast on the board.

Traces on printed circuit boards can break by mechanical or thermal stress.

Thermal stress

Power supplies usually produce a significant amount of heat. Each heating and cooling cycle of the device causes the components of it to stretch a little bit and degrade the materials by bending.

Also heating the device by the environment (sunlight etc.) can cause damage to the device.

Electrolyte of electrolytic capacitors and many types of batteries has a limited range of working temperatures. The electrolyte can boil off when used at extreme temperatures, it can freeze and most importantly, it slowly evaporates even during normal use or storage of the device.

Too low temperatures can cause brittleness of many materials.

Air humidity can condense in the device when used or stored below the dew point.

Humidity and water

Electrical devices are susceptible to damage by water and air humidity. It can cause corrosion, among of other effects.

Chemical damage

Fumes of some chemicals (think of iron chloride) can be very damaging to electronics.

Chemicals are used in manufacturing the device, especially the printed-circuit board, can slowly deteriorate the materials used in it. Solder flux is well-known cause of damage of PCBs.

Electrical overloading

Operating the device out of specs, overvoltage, shorting the output etc. can shorten lifetime of the power supply.

Typical damage of individual components

Electrolytic capacitors

This kind of component is well-known for their tendency to degrade over time, even when the device is not in use. The capacitors are not perfectly sealed and the electrolyte can slowly evaporate. Also, they produce gas over time ­– you can see “bulged” capacitors in some devices. They degrade faster in hot environment (e.g. when the device is in use), but the degradation is inevitable.

bulged capacitor

Source of the image: https://commons.wikimedia.org/wiki/File:D865PERL_bulge_2.jpg

Other capacitors

Some other types of capacitors (e.g. ceramic) can be damaged by vibrations and mechanical stress. They can even develop a short circuit.

Printed circuit boards

Printed-circuit board traces are a very thin foils of metal. It can break by vibrations, mechanical shock etc.

If the manufacturer does not properly cover all surfaces susceptible to corrosion, the PCBs can corrode over time. Improperly cleaned soldering flux can cause corrosion to the board traces.

Air humidity and some chemicals can make some “worse” PCB materials to become conductive.

Inductors and transformers

These components are made by winding a length of wire around a core. Magnetic fields in the coil can cause vibration of the coil itself or nearby metal parts and it can help to damage the device by vibrations.

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  • \$\begingroup\$ Wow, a very comprehensive answer! Does that mean that after more than several tears of being left plugged into the mains, but not powering the device, it's probably on the way anyway? Trouble is, when the recording deck turns itself off, it's back on within 10-20 secs, so not long enough to put a meter onto the DC plug. \$\endgroup\$
    – Tim
    Commented Jul 15 at 10:47
  • \$\begingroup\$ @Tim Many PSUs can survive years of usage without any problems, other fail very quickly. \$\endgroup\$
    – jwo
    Commented Jul 15 at 10:51
  • \$\begingroup\$ If there is a safe voltage on the output side of the supply, try taking cover of the desk off and measuring the voltage it “sees” actually on the plug. It might be possible that the recording desk causes the supply to overload and the supply turns off since it detects a short-circuit condition on its output. \$\endgroup\$
    – jwo
    Commented Jul 15 at 10:52
  • \$\begingroup\$ @Tim Electronics can survive a long time or a short time, with no good way to predict. And - especially older ones without all kinds of computer chips - they can often be repaired. Replacing electrolytic capacitors with new ones is one of the most common repairs in old equipment, and your symptoms too could be caused by worn-out electrolytic caps, although there's no way to know for sure without testing them. \$\endgroup\$
    – user20574
    Commented Jul 15 at 20:51
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Yes, power supplies do wear out. For example LED lamps may start blinking or don't light up because their power supply is not working any more.

Components such as electrolytic caps will degrade over time. But they can also degrade if they are 7-8 years unpowered.

So it's simply that the power supply is at the end of it's useful life.

Or some other component after the power supply.

Some power supplies I've encountered have an interesting quirk that when output capacitors start degrading, the output voltage(s) may also rise until something damages.

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    \$\begingroup\$ The specs for a quality power supply will specify a mean time before failure (MTBF). The number is often frighteningly small. \$\endgroup\$
    – John Doty
    Commented Jul 14 at 14:34

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