Not too long ago one of these darn IKEA LED lamps (200lm, 4.3W) broke down after very mild usage. Well… it has happened again!
When I went into my bathroom one or two hours ago, I thought I was going blind, everything was so dark. But it was the friggin’ lamp…
The power supply looks fine – just like the last time.
No burn marks, charring or blow holes. Nothing!
This time I made an effort to pull all parts off the PCB intact – to check them. I managed to do just that – with two exceptions: the inductor broke (again, see last time), the controller IC (no way to check it).
Empty PCB with a bit of the inductor that didn’t want to come off.
I tested all windings. As far as inductances go, they were all below 5mH. My meter doesn’t go below that. The resistances were fine. The secondary going to the LEDs had 52mR, the other windings 179mR (maybe feedback) and 1.784R (probably primary). All in order.
List of measurements, everything looked fine and in spec.
Bag of parts ready for the recycling center
Last but not least – as previously reported on this blog – the LEDs are still fine!
Is this planned obsolescence or just plain old failure by design?
In response to Jkx’s comment:
The built-in power MOSFET (n-ch) may still be OK. No conductivity between D->S, S->D conducts via its body diode (0.538V), as expected.
There is a resistance of about 500kR between the BP and S pins and a clear diode action, which may be alright, as there is a Zener diode in there. There are some signs of life of the internal 6.5V Zener diode. Reverse-biased current markedly increases at about 7V.
The FB pin behaves similarly, but with different resistances. Resistance between FB and BP is several MR.
The power MOSFET seems to be OK, the Zener diode may still be OK, the rest… who knows. Given that all other discrete parts seemed to be in good shape, the conclusion must be that either the infamous inductor or the control logic in the chip are the cause for this repeated failure.