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Darn switching mode power supplies, anyhow

T

Tom Wells

Zenith VCR died a few weeks ago. Got off my duff Sunday and had a look. No schematic, but darkened PC board material led me to the faults. Swollen 100mfd, 200v 'lectrolytic (dead short) also took out a 2.7 ohm flameproof resistor and the full wave bridge, which was
incredibly undersized ( a 4 pin DIP) , and the 1.6 A fuse. Put in a 200 mfd 450 v cap, a REAL full wave bridge, ceramic resistor, and a new
fuse. Why is it supposed to be so much better to have 50 parts instead of a REAL transformer, when the switcher power supply is a guranteed failure device? Next time I'll figure out how put in a brute-force power supply with a "real" transformer.
Makes me mad when designers put in minimally adequate components in order to stimulate new sales. :mad:
Then there's that notice that says there are no user-servicable parts inside. Sez who?
I ordered a schematic download, which will be useful in the future.
A good head cleaning, and everything's OK. Didn't have to rob parts out of another old dead Zenith VCR we accquired somewhere.
Sure beats buying a new one which would have an even lower margin of quality than the 1997 model.
 
Consumer equipment isn't built to last forever. It's designed to fail after just enough time that the owner doesn't feel screwed. If they didn't build it that way it would be twice as expensive and also the company would go out of business.

There's a certain audio processor manufacturer (a last name is involved) who I'm certain designs their audio processors' sound to gradually worsen over time. That way when their new unit comes out and you try it, it blows away the older one-so you buy the new one.

And you know what? I have NO PROBLEM with that! Why? First off, if they designed their stuff to work well forever, then they would have long been out of business. Second, it gives people like me and Bill Sacks a living refurbishing the old stuff. Third, it insures a ready supply of good value used equipment for the smaller stations.

A win/win/win. What's wrong with that?

It's the American way!
 
Planned obsolesence is a good way to keep me from buying a new device EVER, from the companies that rely on it.
Money comes too hard to not search out products that are over-engineered or easily serviced.
When I find something reliable, I buy more of them.
I prefer to put money into the service economy than continue to throw money at newer, unservicable technology.
And I would glady pay twice the price for a product that actively marketed their more reliable/servicable design over fall-apart brands.
Marketing tends to play up the gee-whiz features that don't add as much real value as rugged design.
Squeezing a nickle until Jefferson says "ouch" has served me well.
So have the boxes and boxes of electronic components gathered over the years, and the donated "dead" electronic devices.
The highly servicable 1960s cars I've kept (and drive, too) have paid me back many times over.
 
I understand planned obsolescence quite well, but what I don't understand is why it's so hard to buy / find
equipment that is a step up from the planned obsolescence models.

Consequently I have hung on to various pieces of equipment I have found, that were built back in the 80s and late 70s, when
things were a little more robust and not built to a price.
A good example is my domestic turntable. It's a Technics SL-1600 MKII. This thing is built like a battleship. Solid, heavy, reliable and
sounds good. Where is today's model? Well, it's the SL-1200 MK V or similar, at some outrageous cost. Actually, it's the only turntable that
Technics make now.

My VCR - which really only gets used for transcription or looking at what's on a tape I might find in a box somewhere is a Panasonic NV-FS100.
Once again, a build like a tank, strong, reliable and still going all these years later. What would I replace it with today? Nothing. They don't make them any more.

Ah the good old switchmode power supply. Someone once said "they are only ever ONE cycle away from going BANG!" I have to agree. They are a Chernobyl waiting to happen. Why do they use them? Simple. Economics.
A switch mode power supply will always be cheaper to build than an equivalently rated one with a copper wound transformer.
Correspondingly, they use components that are rated to within a fraction of the limits of the voltage they will be working under.
If you have a 24 volt rail, they'll use a 25 volt capacitor. It's cheaper than a 35 volt one, and when you multiply the few cents difference between the two caps by the millions of units they turn out, you can see the savings.
 
They sure make the Anvil cases a lot lighter for remotes.
As we've found out, the big heavy transformer supplies survive bad power but the amp blows smoke.
Switching supplies seem to survive 100 feet of extension cords, sharing with inflatables, and bad 2-cycle generators.

Put a fan on the SVHS VCR's heatsink. Keeps the whole thing much cooler.
 
Did the price of copper,killed off the transformer biz. also the weight and size to add to it.I ather work on the transformer jobs then the switch mode jobs anyway.
 
APC's touting their "most efficient desktop" UPS yet (5 times!) with it's "high frequency, low copper design".
Gee, wonder what kind of a supply that is?
 
The single biggest reason for using switchers is that one model can be used around the world without reconfiguration (e.g. 90 to 250 AC 50/60 Hz).

Now, if the USA could make the move to a measurement system not based on the width of the King's thumb (or the length of his feet or the distance from his nose to the tip of his fingers... ... ...) we could improve our ability to sell overseas.
 
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