I have a Lidl worklight of the type that uses a panel of 150 LED's. It worked fine for a while but one day it flickered and went out.
As I'm one of those who likes to see what makes things tick, rather then send it back I had a look inside the housing where there is a small Switch Mode Power Supply (SMPS). Photo here:
I'm hoping someone can advise on the likely faulty component.
Thanks for any help.
Roger R
If the fuse is blown violently i.e. blackened inside, check D1,2,3,4 for short circuit. If they are ok, then likely that IC1 has failed. If it has, that may not be the end of the story. Has the supply got any s.m. components on the back of the board ? If so, and the chip has failed, there will probably be s/c zeners / diodes amongst them. If the fuse has failed gently, you might just be lucky and have something like a s/c secondary side diode - red one top left, black one bottom left - although if the chip has got any 'inteligence', usually secondary side overloads will result in a cycling shutdown rather than excess primary side current.
Arfa
In article , Roger R writes
Agreed with Arfa. If the mains fuse is silvered/blackened on the inside of the glass (hard to tell from the photo), it's a short in the primary side, most likely one of D1/2/3/4. D2[obscured] looks like it's been farted about with, have you had someone look at this supply already?
There's no primary-side switching transistor, which is unusual. Maybe it's inside IC1, but your picture isn't clear enough for me to read the markings on IC1 to look up the spec.
IC1 also looks slightly brown on the surface, as if it's overheated. It's certainly a suspect.
There also appear to be two D2s, unless the green capacitor C4 is obscuring another number of diode D2x, the one I refer to as D2[obscured] above.
Nasty cheap design, intended to just get you past the warranty period before expiring.
If for some reason you dont get the smpsu fixed, it could be run without it by substituting a simple CR supply, reconfiguring the LEDs and making sure the LEDs were sufficiently insulated.
NT
I thought that, too. It is off-board somewhere, or soldered onto the reverse side of the PCB (which would also be unusual)?
But yes, that or rectifier diodes. I'm not sure if that's some kind of thermistor near the fuse; if so it *might* have gone bad, although that's less likely.
Worth checking the main smoothing capacitor, too; whilst it may not have shorted, it may have gone bad and be the cause of failure in whatever component *has* made the fuse blow.
It could be a fault on the LV side, too - but checking the obvious on the HV side should be quick and easy and is more likely I think.
Looked like a prefix of V1F / VIF / VTF / VLF and then -22A to me, but none of those cough up anything via Google unfortunately. Seems unusual that an IC would no heatsink could do the job of switching, though. Unless the heatsink fell off, which is why it's cooked :-)
cheers
Jules
Not unusual these days Fred. There are many 8 pin (usually actually only 7 pins but a 'standard' 8DIP package) 'switchers-on-a-chip' now. They are used extensively in LCD TV smps to implement the PFC front-end or standby supplies. The TNY266 is a typical example of this sort of chip. Modern FETs have such low resistance switched drain-source channels, that very little power is dissipated in the device itself. These supplies can achieve efficiencies in excess of 90%. So as long as you can make sure that there is enough insulation resistance around the package pins to which the switching FET is internally connected - and that's why they have the 'missing' pin 7 - then using them in a switcher man enough to drive those LEDs, is something that they can easily cope with.
At the moment, I'm still erring towards the problem being one of the front-end reccies though, as *usually*, although not always, s/c failure of those chips is very evident in that all of the magic smoke will have escaped from the gaping hole in the top ... :-)
Arfa
Thanks to the replies, To answer your points:
The fuse glass is perfectly clear, no violent blow. But it is blown.
There are no components located elsewhere and nothing on the back (not even tiny surface mounts).
As noted there are two occurrences of D2 marking on the board.
-D2 not disturbed - nothing at all has been touched on the board.
The bridge rectifier diodes D1-4 are type 1N4007. Diode D2 (2) also looks like its 1N4007, but can't really be seen. Diode D3 is different type FR10...something
The small diodes seem to measure ok - like 640 something one way and nothing the other.
The large Ultra high speed rectifier diode D7 (bottom left of the blue transformer) is type UF5404
IC1- ( VIPer22AS) brown writing - just a trick of the light I think - not burnt.
It doesn't look like the large capacitor has failed.
My suspect is an insulation breakdown in the chopper transformer. If so, I won't be able to get one and will have to send it back.
My website pictures updated.
Roger R
They don't always blow apart. ;-)
So, if the fuse hasn't failed violently, but is definitely open, have you tried just replacing it ? Not unknown for fuses to fail for no apparent reason. May just have been a metal fatigue thing, or a defectively manufactured fuse, or even a short term event like a surge or spike on the mains. It is virtually unknown for an input fuse on a switcher to fail in this way, if there is genuinely anything wrong with the supply ...
Arfa
There is, it's in the ST Viper Chip, it's pretty much all the control gear and power bits for a small SMPSU. I'd replace the chip, the diodes D1-4 and check the rest of the diodes, primary and secondary.
Roger R formulated the question :
In that case my first step would be to replace the fuse and see what happens - it just be a faulty fuse which has failed.
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