The SMPSU equivalent of 'fingernails on the blackboard'

[linker3000]

Just looking at this one sets my teeth on edge.



This board is from a no-name RGB LED DMX PAR lamp (they're all over your favourite auction site and tat bazaars); it's rated at 12V 3A and joined the afterlife with a whomp. The IEC inlet contained a 1A fuse (vaporized), but the board also had a through-hole one, which was similarly toasted. There's no inrush limiting, nor mains EMI filtering. As a sidenote: the lamp unit has an IEC socket and a plug to allow for daisy-chaining, but the earth pins aren't linked, so it would be all fun and games if something down the chain wasn't all-plastic and needed a ground connection!

I plan to ultimately replace the board with a decent (anything would be better!) module but decided to repair this one just for the experience as I have most of the parts in stock. In the pic, the board is waiting for a new power FET and mains smoothing cap (it had a fake Nichicon). I have replaced one shorted 1N4007 and the others will be replaced too - note the lead thickness on the new diode (bottom) compared to the originals (tight-ass cheapies). The output caps will also be changed and I'll check/change the shunt reg and opto as necessary. The electrolytic cap top left is screen printed 10uF/50V, but the one originally fitted was rated at 25V (I've put in a new 63V one); out of curiosity, I'll measure the voltage across it once the board's working again. The PWM chip is a CR6853T.

At the moment I've put a link in the on-board fuse position, but considering there's already a fuse on the power socket, I'll replace it with a 10R power resistor. The original board had flyleads soldered on for AC in and DC out so I'll use the AC holes to mount some rudimentary filtering and a MOV.

Yeah, I know this one's not really worth repairing, but it was a case of 'challenge accepted'.

[momaka]

Re: The SMPSU equivalent of 'fingernails on the blackboard'

Yeah, I know this one's not really worth repairing, but it was a case of 'challenge accepted'.

Yes, sometimes it can be fun to repair these things, even though you know the time and parts you put in them still may not make the unit compare to a properly-built one.

But keep us posted on how it goes, nonetheless.

note the lead thickness on the new diode (bottom) compared to the originals (tight-ass cheapies).

Those thin leads are for extra safety - you know, in case the main fuse doesn't blow, these leads will for sure .

it's rated at 12V 3A

Are you sure there isn't a really tiny zero and a dot somewhere in front of the "3A" rating?
I don't think those output diodes will handle 3A - not continuous anyways.