Funny things fault currents...

A while ago SWMBO turned on the light on the cooker hood, and one of the
bulbs decided it was time to play lemming. Flash bang, dead cooker hood.
So I replaced the bulb, still no joy. Thought, aha, it must have taken
out the fuse in the plug... checked it - working fine. At that point I
lost interest for mumble months. Anyway today I located the required
round tuit needed to permit further investigation. No internal fuses to
be found, and volts were getting as far as the input connector. The
little circuit diagram sticker in the box showed nothing else between
mains and lamp save for a switch. So having extracted the switch box
(and removed enough years of cooking goo to make it touchable), I pulled
it apart to check the switch. Switch was fine, but the big black stain
of vaporised metal inside the case was a bit of a clue! There was also a
nice clean bit of PCB with no solder resist on it, and more critically,
no copper either! So the bulb short had taken out about a cm of 3mm PCB
track leaving the 5A fuse unharmed.

Repair involved de soldering incoming wire attached to a now completely
pointless annulus, and tacking it onto the back of the board a bit
further along the track. Result, happy SWMBO.


--
Cheers,

John.

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John Rumm wrote:

A while ago SWMBO turned on the light on the cooker hood, and one of the
bulbs decided it was time to play lemming. Flash bang, dead cooker hood.
So I replaced the bulb, still no joy. [...] At that point I
lost interest for mumble months. Anyway today I located the required
round tuit needed to permit further investigation. [...] There was also a
nice clean bit of PCB with no solder resist on it, and more critically,
no copper either! So the bulb short had taken out about a cm of 3mm PCB
track leaving the 5A fuse unharmed.

I had the same thing, including the mumble months of hiatus. In my case,
after repairing the burnt track the lights cannot be turned off - my guess
is that the switch contacts have fused closed.

Luckily they are screw-fitting halogens, so a 1/4 turn does the trick. I
think I need a whole new level of motivation to contact Baumatic for a new
switch.

no copper either! So the bulb short had taken out about a cm of 3mm PCB
track leaving the 5A fuse unharmed.




I've spent many happy hours repairing older out-of warranty high-end audio
amps ( Naim, Carver etc ) and have always assumed that power semiconductors
were there to protect the fuses...

--
Ron

"John Rumm" wrote in message
...
Funny things fault currents...

A while ago SWMBO turned on the light on the cooker hood, and one of the
bulbs decided it was time to play lemming. Flash bang, dead cooker hood.
So I replaced the bulb, still no joy. Thought, aha, it must have taken
out the fuse in the plug... checked it - working fine.

In our case the failing bulb just blew the plug fuse, still a PITA as the socket
is behind the 'chimney'. In a separate fault I also had to resolder the motor
contacts as there was a dry joint.


--

Michael Chare