"Roger R" wrote in message
...

"Jules" wrote in message
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On Fri, 18 Sep 2009 13:27:48 +0100, Fred Bloggs wrote:
There's no primary-side switching transistor, which is unusual.

I thought that, too. It is off-board somewhere, or soldered onto the
reverse side of the PCB (which would also be unusual)?


Thanks to the replies,
To answer your points:

The fuse glass is perfectly clear, no violent blow. But it is blown.

There are no components located elsewhere and nothing on the back (not
even
tiny surface mounts).

As noted there are two occurrences of D2 marking on the board.
-D2 not disturbed - nothing at all has been touched on the board.

The bridge rectifier diodes D1-4 are type 1N4007.
Diode D2 (2) also looks like its 1N4007, but can't really be seen.
Diode D3 is different type FR10...something

The small diodes seem to measure ok - like 640 something one way and
nothing
the other.

The large Ultra high speed rectifier diode D7 (bottom left of the blue
transformer) is type UF5404

IC1- ( VIPer22AS) brown writing - just a trick of the light I think - not
burnt.
http://tinyurl.com/lnrne3

- I am reluctant to unsolder any component to test as the unit is still
under warranty and I can send or take it back, but I hope to identify the
fault, satisfy my curiosity and save the trouble of returning it

It doesn't look like the large capacitor has failed.

My suspect is an insulation breakdown in the chopper transformer.
If so, I won't be able to get one and will have to send it back.

My website pictures updated.

Roger R



So, if the fuse hasn't failed violently, but is definitely open, have you
tried just replacing it ? Not unknown for fuses to fail for no apparent
reason. May just have been a metal fatigue thing, or a defectively
manufactured fuse, or even a short term event like a surge or spike on the
mains. It is virtually unknown for an input fuse on a switcher to fail in
this way, if there is genuinely anything wrong with the supply ...

Arfa