[GreenKeys] Off topic: variable transformer

[Jeffrey D Angus]

On 7/28/2016 12:20 AM, Craig Sawyers wrote:
> Alternatively you can just cross your fingers and turn it on,
> and wait for sparks and smoke.
That's certainly one method, although not the preferred one.
> There can be problems that a variac will help diagnose well
> before any valve rectifier and regulator. Such as transformer
> problems like shorted turns (had that) or open circuit (like
> on a Quad II power amp) or perished wiring. Or if solid state,
> a bridge rectifier with an open or shorted diode (had that),
> or a switched mode supply with a shorted bridge (had that too).
All of this SHOULD be checked BEFORE applying power.
> And if a switched mode supply sets fire to itself with the
> wrong voltage, what happens in a brown out as the mains fails
> during a storm, or when there is a power failure and the mains
> cycles on and off several times before it comes back up?
What if, what if what if.... All the hand wringing in the world is NO 
substitute
for proper diagnosis and troubleshooting.
Properly designed switch mode power supplies shut themselves off under
brown out conditions. But they weren't properly designed yet in the '80s.
You could kill just about any PC AT power supply by rapidly flipping the
power on and off repeatedly.
Most current switched mode supplies have a window of "I operate right
or I shut down" now.


-- 
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com