How are non-engineers supposed to cope?

The Central Vac

Today the central vacuum system stuck ON.
The hose was not plugged in, and toggling the kick-plate outlet in the kitchen did not fix it.  That accounted for all the external controls.
The way this works is there is a big cylinder in the basement with the dust collection bin and large fan motor to pull air from the outlets, through the bin, and outside the house.  This is a great way to do vacuuming, because all the dusty air gets exhausted outside.
The control for the fan motor is low voltage that comes to two pins at each outlet.  When you plug in the hose, the pins are extended through the hose by spiral wires that then connect to a switch at the handle.  You can also active the fan by shorting the pins in the outlet with a coin.  Each outlet has a cover held closed by a spring.  You open the cover to insert the hose.  The covers generally keep all the outlets sealed except the one with the hose plugged in.
The outlets are all piped together with 1 1/2 inch PVC pipe to the inlet of the  central unit.  The contact pins at all the outlets are connected in parallel, so shorting any of them turns on the motor.
We also have a kickplate outlet in the kitchen – turn it on and sweep stuff into it.  The switch for that is activated by a lever that also uncovers the vacuum pipe.
I ran around the house to make sure nothing was shorting the terminals in the outlets.
Next, I went to the cellar to look at the central unit.  Unplugging it made it stop (good!) but plugging it back it made it start again.   That was not good.
I noticed that the control wires were connected to the unit via quick connects, so I unplugged them.  The unit was still ON, which meant the fault was inside the central unit.
I stood on a chair and (eventually) figured out that the top comes off, it is like a cookie tin lid.  Inside the top was the fan motor (hot!) and some small circuit board with a transformer, some diodes, and a black block with quick connect terminals.  The AC power went to the block and the motor wires went to the block.  I imagine that the transformer and the diodes produce low voltage DC for the control circuit, and the block is a relay activated by the low voltage.
Relays can stick ON if their contacts wear and get pitted, or there could be a short that applied power to the relay coil.
I blew the dust off the circuit board, and gave the block a whack with a stick.
That fixed it.
I just don’t see what a non-engineer would do in this situation, except let the thing run until the thermal overload tripped in the fan motor (I hope it has one!) and call a service person.  Even if the service folk know how to fix it without replacing the whole unit, it is going to cost $80 ro $100 for a service call.
I don’t have any special home-vacuum-system powers, but I have a general idea how it works, and a comfort level with electricity that I don’t mind taking the covers off things.  This time it worked out well.

The Dishwasher

For completeness, I should relate the story of our Kitchenaid dishwasher.  One day something went wrong with the control panel, so I took it apart.  It wasn’t working, and I thought I couldn’t make it much worse.  I was wrong about that.
I didn’t really know the correct disassembly sequence, and I took off one too many screws.  The door was open flat, and taking off the last screw let the control panel fall off, tearing a kapton flex PC board cable in two.  The flex cable connected the panel to some other circuit board.  I spent a couple of days carefully trying to splice the cable by scraping off the insulation and soldering jumpers to the exposed traces, but I couldn’t get the jumpers to stick.  New parts would have cost about $300, and the dishwasher wasn’t that new.  We eventually just bought a new Miele and that was the Right Thing To Do, because the Miele is like a zillion times better. It has built in hard-water softeners, and doesn’t etch the glasses, and doesn’t melt plastic in the lower tray, and is generally awesome.
So OK, sometimes you can fix it yourself, and sometimes you should really just call an expert.  How are you supposed to know which is the case?

The Garage Door Opener

Every few years, the opener stopped working.  It would whirr, but not open the door.  The first time this happened, I took it apart.  Now you should be really careful around garage door openers, because there is quite a lot of energy stored in the springs, but if you don’t mess with the springs, the rest of it is just gears and motors and stuff.
On mine, the cover comes off without disconnecting anything.  Inside there is a motor which turns a worm gear, which turns a regular gear, which turns a spur chain wheel, which engages a chain, which carries a traveller, which attaches to the top of the door.  The door is mostly counterbalanced by the springs.  With the cover off, you could see that the (plastic) worm gear had worn away the plastic main gear, so the motor would just spin.  The worm also drove a screw that carries along some contacts which set the full open and full closed travel, which stops and reverses the motor.  The “travel” adjustments just move the fixed contacts so the moving contacts hit them earlier or later.
An internet search located gear kits for 1/3 or 1/4 the price of a new motor, and I was able to fix it.
Last time the opener stopped working, however, the symptoms were different – no whirring.  The safety sensors appeared to be operational, because their pilot lights would blink when you blocked the light beam.  I suspected the controller circuit board had failed.  A replacement for that would be about 1/2 the cost of a new motor unit and I wan’t positive that was the trouble, so I just replaced the whole thing.  The new one was nicely compatible with the old tracks, springs, and sensors.
A few weeks later, my neighbor’s opener failed in the whirring mode, so we swiped the gears from my old motor unit with the bad circuit board and fixed it for free.

Take aways

Don’t be afraid to take things apart, at least if you have a reasonable expectation that you are not going to make it worse.
Or – Good judgement comes from experience, but experience comes from bad judgement. (Mulla Nasrudin)
… and just maybe, go ahead and get service contracts for complicated things with expensive repair parts, like that Macbook Pro or HE washing machine, particularly when the most-likely-to-fail part is electronic in nature.
So I usually get AppleCare, and we have a service contract for the new Minivan, and for the washing machine, but <not> for the clothes dryer, since it doesn’t appear to have any electronics inside.  I was able to fix that by replacing the clock switch myself.
But how are non-engineers supposed to cope?