On Fri, 02 Feb 2018 16:05:24 +0000, T i m wrote:

On Fri, 2 Feb 2018 15:29:34 +0000, ss wrote:

snip

Update:
So fuse arrived today, soldered in to the charger, switched on and POP!

As some predicted it might. ;-)

That will be for the bin then as now beyond my understanding of electronics.

Before you do ... do you or a friend have a Digital Multimeter (or if
you have anything with a battery in it, get one yourself anyway). Put
it on Diode test, or the lowest value of ohms and test both ways
across all four of the diodes (with it disconnected from the mains of
course). If all is well with the diodes you should see a reading in
one direction and different in the other (equally on all 4 diodes),
but not a short circuit across any. Any showing as a short circuit are
probably faulty and can be replaced easily and cheaply. (You might
also just desolder one end of each diode that shows as a short and
test it like that in case the short is coming from elsewhere).

It's not difficult to do and might only cost pence if it turns out to
be a diode (or two).

At least it never exploded this time.

;-)

Ok now waiting on replacement fuse & holder for the other charger,
fingers crossed.

So time to test the diodes in the other charger. ;-)

Cheers, T i m

While prodding around under the board, stick the meter across the legs
of the device attached to the heatsink.

There should be a high reading from possibly the center pin to the
other two. If Q1 is a transistor that is!

The bit that has the Volts on will go to the ferrite transformer.

All three legs reading low Ohms to each other is a fault and may be
more likely than a blown rectifier.

Having said that, if you have a dodgy plug connection or are using one
of those adapters using copper foil to make contact, it's yer diodes.

If the transistor is S/C, it may just be that but its worth checking
the low Ohms resistors in the emitter. These often fail when the full
whack of current goes through Q1.

Finally if the "transistor" is S/C, it is also worth checking the
shaping network on the collector.

On this diagram the items are R12 and C9.

https://www.bing.com/images/search?v...x=0&ajaxhist=0

The resistors here frequently went o/c and this led to a very short
lifespan for Q3 in the diagrams case, or Q1 for your board.

On a final note, it would appear that Q1 is a bog standard transistor,
but all sorts of things get included in epoxy packages these days.

On the plus side, it may have a part number stamped on :-)


The last SMPS I bought from Ebay was less than £5-00.

When I repaired them for a local industrial electronics company, the
repair would cost the client forty time that sum.

Happy days :-)


AB