Hi Butch.  I had a major failure in a 70 amp Astron linear supply several
years ago.  Based on the smell that wafted out of it, I'd bet that it was
momentarily on fire, HiHi.  I didn't bother to repair it, just sold it at a
hamfest for $5 just to get rid of it.

Alan/KD7GC



Alan R. Downing
Phoenix, AZ

-----Original Message-----
From: For blind ham radio operators [mailto:[log in to unmask]]
On Behalf Of Butch Bussen
Sent: Wednesday, April 02, 2014 2:25 PM
To: [log in to unmask]
Subject: Re: Power Supplies (Switching or Not)

Yep, certainly possible, but I have used many many conventional supplies 
on my own station and in many commercial instalations, and I've never 
had the ovp fail.  If i replaced pass transisters, I always used 
darlingtons.  They genally opened rather than shorted if they went bad 
at all.
73
Butch
WA0VJR
Node 3148
Wallace, ks.


On Wed, 2 Apr 2014, Martin G. McCormick wrote:

> 	Another good thing about switching supplies is that they
> ten to fail safer. Linear regulator supplies can end up with
> shorted output transistors that put the full unregulated output
> of the rectifiers and filter capacitors on your nice expensive
> radios. There is usually a huge SCR with a circuit designed to
> fire the gate of the SCR if the voltage exceeds maybe 14 or 15
> volts which causes the SCR to short the output and blow a fuse,
> but still that is pretty extreme.
> 	What if the SCR blows first?
> 	Switchers are more apt to just quit when something goes
> wrong. They may also make smoke and blow fuses or capacitors but
> they aren't likely to keep running and deliver high voltages to
> the load turning it in to a hot paper weight.
>
> 	As for repairing switching supplies, the poorly-designed
> cheapies will probably start cooking their electrolytic
> capacitors and begin to die soon after purchase but well-made
> supplies from good components should last decades. The
> beginnings of a switching supply are very much like the power
> supplies that used to run CRT-based televisions. They tend to
> either be 100% up or 100% trash and they can switch from one
> existential state to the other in a flash and I mean that
> literally.
>
> Martin WB5AGZ
>
>