George wrote:
"Dave Liquorice" wrote in message
ll.net...
On Fri, 28 Mar 2008 18:21:42 +0000, Adrian wrote:

Don't know 'why' it's failed - could be the cap itself or 'something
else'
I'd put money on something else, looking at the cap wires, the burnt
board, coloured deposit and general sticky yuk of the board particulary
top right corner. I'd say some liquid has got in at some point and caused
a flash over between the pins of that C.

It appears it may have worked for a while but now the fuse blows at switch
on. Suspect a knackered SMPSU, so probably require a new pair of driver
transistors, the control IC and other sundry bits to get back working. If
it takes more than a morning in total to repair it's not economic, there
are other reasons for fixing things besides money though.



No chance of just faulty cap then? ;-)



If it is a switched mode power supply, then like as not a whole bunch of
stuff has invisibly failed somewhat before the cap gave up the ghost.
Up to and including everything on the hot side of the ferrite
transformer, and the transformer itself.

Try all the rectifiers, the mains rated capacitor and the power FET..and
probably any chip associated with it as well.

Things were simpler before SMPS..fixing valve stuff was almost all about
'replacing valves till it worked'

The rot set in with transformerless semiconductor power amps. Ther you
simply replaced all the actives, tested them, and put the still
functioning bits back into the spares box.

Then came SMPS and chips which you couldn't buy easily..and then surface
mount. That you couldn't unsolder easily anyway..

"The Natural Philosopher" wrote in message


Then came SMPS and chips which you couldn't buy easily..and then surface
mount. That you couldn't unsolder easily anyway..







If you need SMD components? try this place...

http://tinyurl.com/29u73c

Normally I won't fix SMD stuff as you have stated, not easy to desolder the
components without the relative soldering iron tips but even when you have
these the components are very compacted together on the pcb its very hard
not to touch other components in the vicinity.

I have a 19" widescreen LCD monitor Id like to fix as when it was working
the picture was crisp and full of life in terms of richness in colour and it
truly was a exceptional picture.
Alas I cant seem to fathom out where the problem lies,its stuck in the on
mode as per the green led but is completely dead no back light and no sign
of screen life which you can normally get a very faint image if you suspect
the backlight is at fault.
:-(

I used to mend modems years ago, we used to get some back from Italy
with flash-over damage, it was not a problem with the modems from UK
users.
..
It is quite likely that the flash over damage you see was caused by
condensation, and that it has nothing to do with the current problem,as
the blue-ish copper sulphate-like deposit would take time to form.

It might indicate that a "transorb" or similar device has failed open
circuit.

I'd check all the semiconductors or simply replace them all anyway.

you can get all the bits from Grandata they may even do a "repair kit"
if it's a popular enough problem.

http://www.grandata.co.uk/ -they're good on the phone if your not sure
what you need



In message , geoff
writes
In message , George
writes

"Geo" wrote in message
news
On Thu, 27 Mar 2008 22:17:35 GMT, "George" wrote:

What value is this this Cap,its marked "104K" and is on the bridge
rectifier
side of power supply of a portable TV.

.1uF

Its leaky as noticable on the PCB

Unusual for a ceramic (no liquid to leak)

Geo

Sorry for the high definition.
http://www.20xx20.myby.co.uk/cap.jpg

Looks like copper salts (from the wire?)

is that a burn I see between the legs ?

Liquid has dripped on it or something


--
Neil J. Harris

On Sat, 29 Mar 2008 11:52:19 GMT, George wrote:

No chance of just faulty cap then? ;-)

The C, apart from the arc burnt leads, looks fine...

--
Cheers
Dave.

On Sat, 29 Mar 2008 10:04:02 +0000, The Natural Philosopher wrote:

The worrying possibility is a short between primary and secondary on the
mains transformer.

The C in question is on the primary (live) side as indicated by the
cross-hatching. It could well be across the DC side of the bridge
rectifier formed by 4 1N4006 diodes sp will have something like 320V to
340V across it. SMPSU's are scrary things, mains comes in, is bridge
rectified and smoothed before feeding the chopper transistors...

--
Cheers
Dave.