"Arfa Daily" wrote in message
...

"b" wrote in message
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On 1 oct, 02:53, "Arfa Daily" wrote:
"ian field" wrote in message

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"b" wrote in message
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I'm repairing a dead philips VR 600, the SB340 diode on one PSU
output
gave s/c both directions, I don't have one in my spares box...anyone
know of a suitable equivalent?

datasheet:
http://www.datasheetcatalog.com/data.../4/SB340.shtml

cheers,
B

I googled "3A 40V shottky barrier" and got several results on the
first
page.

It's a very common problem on Philips PSU's. Replacement type is not
critical. Just about anything of similar rating, intended as a smps
secondary reccy, will work perfectly well in my experience.

Arfa

just tried a BY255, but got erratic operation and overheating -
probably couldn't handle the frequencies of the SMPS..... today I
bought an exact replacement schottky so will post back when
installed. Ben

???????????????
I guess I wasn't clear enough when I said

"intended as a smps secondary reccy".

The *exact* type is, as I said, not critical. The *generic* type of course
*is*. A secondary-side reccy in a smps *must* be a high speed job,
typically a Schottky type, as you were originally asking about. Sorry if I
implied otherwise ... :-)

Arfa


Very occasionally some manufacturers get it wrong with SB rectifiers, its
sometimes helpful to check the peak reverse voltage using a simple peak
detector consisting of nothing more than a rectifier and capacitor in series
directly across the rectifier under test, the measured peak voltage must be
added to the rectified voltage - the sum of which must be less than the SB
rectifier's rated voltage.

If the voltage is excessive check the primary snubber first, if that's OK
then the manufacturer has got it wrong - the options are fit an SB rectifier
with sufficient voltage rating or add a shunt resistor to the capacitor in
the peak detector and leave it in place as an individual snubber just for
that rectifier.

Sometimes manufacturers are not too sure of their own design, one Philips
DVD I worked on had holes and screen print for either the 3A leaded package
or a TO220 type. The 3A type had failed so I made use of the TO220 position
with a 6A rectifier - the repair didn't bounce.