"N_Cook" wrote in message
...
Ian Field wrote in message
...

"Arfa Daily" wrote in message
...
Had a JTS radio mic receiver on the bench today. "No power", said the
job
ticket. With 12 volts going in, the output from the four-legged LDO 8
volt
regulator, was almost nothing. A quick stab around with the ohm-meter
revealed about 1.7 ohms across the output. Nothing obviously short.
Nothing getting hot because the regulator was in a full foldback
condition. Loads of surface mount 4558's in there, as well as a good
selection of more exotic ICs, and the 1.7 ohms could be measured at any
of
them. I had a quick word with the shop that it came from, and the guy
there was of the opinion that it would not be worth pursuing even with
the
manufacturer, as it was well out of warranty. "He'll just have to buy a
new one" he said. That made me feel bad, as I felt that I had perhaps
not
pursued it far enough.

On the basis that the job wasn't going anywhere anyway, and time had
already been spent, I decided to get brutal with it, to see if I could
make the short show its face. I turned the power supply down to about 4
volts, and linked across the regulator. I then turned the supply back
on
and settled down to wait. As it turned out, it wasn't for very long ...
A cloud of smoke and sparks shot out of a tiny little surface mount
solid
tantalum 1uF cap.

That method has located many S/C zeners for me.




A non contact IR thermometer can be useful for such and similar low ohmic
VTS , to wave over the errant board


Maplin didn't stock those back in the days when I used brute force &
ignorance to weed out dud zeners.