Recovered from red LED on MyCloud

I came back from  a short holiday only to find a red light on MyCloud front panel. A quick search in this forum confirmed that the drive was most likely broken for ever.
Quite by chance, I plugged the MyCloud cable into my old MyBookWorld  and was surprised to see that MyBookWorld would not fire up. Could the power supply be at fault? I tried the reverse: plugging the old MyBookWorld cable into MyCloud and MyCloud started up with a nice steady blue light.
I have now bought a new cable and am pleased that MyCloud has fully recovered.
Questions still remain: what happened to the old MyCloud power supply, and why was it sufficient to start MyCloud up to get a red light?
Another question is: the original (broken) MyCloud power supply was rated at 36 W output whereas MyCloud itself is rated at 18 W. The new power supply is 18 W; will it burn out?

before you replaced the power pack did you try leaving the myclud off for an hour or more? over heat will give a red light.

as long as the wattage of the new pack is equal or higher then the device you are ok. in this case they are equal and the power pack may get a little warmer as it is running at design load.

FYI, when swapping power packs always be sure the voltage and polariety match and the current is eual or higher then the device or old power pack

Yes, I did leave MyCloud off for over an hour - this was mentioned several times in forum posts. But it didn’t feel hot. Neither it nor MyBookWorld work properly on the old cable.

I also tried a reset. I suspect you can’t reset with the red LED light on. Reset from cold (holding in the reset button, plugging in, then holding the reset button for 40 seconds) didn’t seem to have done anything. My users and shares are now intact. I did successfully reset the device when I first got it a couple of years ago.

It’s a sad but true fact that one of the most common faults in electronic equipment is the simple capacitor… And, in modern switched-mode power supplies used in ‘wall wart’ power supplies, or small, inline supplies, it’s common to rectify the AC input to give a high DC voltage (e.g. about 350V in the UKC), and then switch this voltage to generate the low voltage DC output. Now, the rectification requires a smoothing capacitor, and those are commonly 400V rated. but they’re small, and they’re fairly stressed in operation. With age, they tend to lose capacity, often due to fading electrolyte, which means they don’t smooth the voltage well enough, and peak currents start to rise as the regulation circuit tries to compensate. Eventually, a good regulator wil detect an over-current state, and will stop working, and a poor regulator will blow its primary switching device, often destroying itself in the process, and charring the PCB… I’ve seen these failures a number of times.

Capacitors are cheap, but, when you’re designing to a budget, it’s easy to look for the cheapest device, rather than going for a bigger, over-rated, higher quality component. And power supplies are often bought from generic manufacturers, rather than being designed and made by the company producing the thing it powers…

It may be that your power supply is suffering from a failing capacitor, such that it can produce enough output to fire up the processor, but not enough to spin up the drive. These faults are quite hard to diagnose without being able to measure the output voltage under load, and, even then, a simple DC voltmeter may give a ‘normal’ reading, so an AC reading can help; you shouldn’t have too much AC on a well-regulated supply under load.