Author Topic: Magic Smoke Release  (Read 863 times)

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Offline andersjm

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Magic Smoke Release
« on: September 02, 2017, 09:32:37 am »
Hi forum,

Thought I'd share some pictures I took of the circuit board in a fluorescent light fixture that stopped working in our house. We got a new one under warranty, but since I was curious why the old one stopped working, I disassembled it.

I can't really see which component blew. could it be the transformer?

High res images:


Offline andersjm

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Re: Magic Smoke Release
« Reply #1 on: September 02, 2017, 09:45:00 am »
Looking at it a bit more, it seems like the thin L-shaped trace close to the mains input has blown.

Could they have been using a thin trace as a sort of cheap fuse?

I checked out the diode bridge, it seems to work. The transformer-like-thing (which I think is actually some kind of input filter) also seems okay.

Well, I'm not going to attempt any repair, just curious why it failed.

Offline Ian.M

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Re: Magic Smoke Release
« Reply #2 on: September 02, 2017, 11:31:22 am »
Either something has gone dead short on the output side of the bridge (or the input filter cap shorted), blowing the 'fuse' track, or the 'fuse' track blew on a switch-on surge.  The plasma then triggered an arc across between L and N, which probably tripped your breaker.   

Check the filter cap and the chopper transistor.  If neither are shorted, repair could be as simple as cleaning the board and fitting a single strand of tinned copper wire of an appropriate diameter to replace the fuse track.  See  If the chopper transistor is shorted, its probably BER, as they often take out the control chip when they blow.
« Last Edit: September 02, 2017, 11:32:54 am by Ian.M »

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