# Dead LED power supply Critique of design wanted

#### jeffkrol

Joined Dec 8, 2015
14
An acquaintance of mine had an aquarium light that the power brick failed.
Here's the gory pics..
What do you think?

#### wayneh

Joined Sep 9, 2010
17,152
I don’t repair these anymore. Shop around and you can probably get one with higher capacity for under $10. Thread Starter #### jeffkrol Joined Dec 8, 2015 14 I don’t repair these anymore. Shop around and you can probably get one with higher capacity for under$10.
Sorry, was looking for a critique of the overall design..Thing smoked pretty bad and the diode rectifier had de-soldered itself..
No fuse on the ac side.

Rated 36V 4A out.

#### #12

Joined Nov 30, 2010
18,221
It's impossible to critique a design with no schematic and no specs for any part whatsoever.

That said, the fact that the rectifier unsoldered itself is an indicator of an inexperienced designer at the circuit board level. I've seen a lot of cracked and unsoldered joints in 50 years and it's always related to heat. In the 1970's it was 2 watt resistors on TV and radio circuit boards. In the 2000's I saw unsoldered compressor relays on circuit boards in refrigerators. I have resistors rated at 2 watts and they are nearly as large as 1 watt resistors. That only means the resistor can survive at a higher temperature than they used to. What it doesn't mean is, "Circuit boards dissipate heat twice as well as they did 50 years ago."

Give a beginner a design program and they will believe it like it was handed down by Moses because they don't have any wisdom that comes with experience. Either that or the penny pinchers are telling them not to think because it costs money to guard against a heat problem that isn't going to fail within the warranty period.

#### ci139

Joined Jul 11, 2016
1,696
if the primary of the flyback transformer developes short turns ... say because of 24/7 operation and insufficient cooling -or- continuous - a bit above normal - mains voltage or the aging (secondary side) filter capacitor - the feedback loop is cut and the thing destroys itself in a flash .. . . there might be other failure mechanisms

i had 2x 12V 1A led supplies - 1-st failed in less than a year (it had a glued together fractured ferrite core ???) - the second one still works

#### MisterBill2

Joined Jan 23, 2018
8,759
An acquaintance of mine had an aquarium light that the power brick failed.
Here's the gory pics..
What do you think?

OK, a critique of the device is that it does have an input filter but not an adequate one, and it looks like it may have a MOV to protect from line spikes, but if that small tan block next to the yellow block capacitor is not a fuse then it is not protected. Most of the control circuitry is surface mount on the underside of the board and so it can't be seen. If you have the specifications you can get another supply and be back lighting the LEDs.

#### ci139

Joined Jul 11, 2016
1,696
the input filter is the
covered by the white foam (on the picture above-right next to the yellow lo ESR cap)

Joined Jul 29, 2019
64
Looking at your pictures I would guess that the bridge rectifier failed and shorted ac to the dc side and took everything downstream. Have you metered this component to see if it failed? I would not recommend repairing this supply as it is far to damaged and could still pose a danger from fire.

#### Tonyr1084

Joined Sep 24, 2015
5,973
There's an easy way to get a hold of a replacement for free. I get those power bricks all the time (whenever I want or need one that is) by going to Xfinity stores and asking them if I can have one or two. DirecTV used to have them but I think they're building their power supplies into their units now. Just about any internet provider who also provides modems typically have used ones. They don't reuse them, they just dump them. Taking one or two off their hands every now and then helps them recycle. They ARE used. They can't be reused as a new unit because of potential failure. So they just toss them. I think I have three or four of them laying around right now. In fact, I just got another one for my security camera - been having issues with playback features and the manufacturer is reluctant to help me. They sent me a new unit with a new PS. So I'm almost finding them stuck between my teeth.