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COB LED Autopsy

The intent was to wire the “5 W” COB LED to the 12 VDC supply grafted on the Juki TL-2010Q, through a suitable resistor around 18 Ω. Unfortunately, the next morning I managed to run 12 V directly to the LEDs, which produced an astonishingly bright flash of blue-white light and an opportunity for some post-mortem analysis.

A sharp tap with a chisel popped the COB LED PCB off its heatsink:

Destroyed COB LED - epoxy bond
Destroyed COB LED – epoxy bond

That’s a pretty nice thermal joint and ought to transfer as much heat as reaches the back surface. Mechanically, it yanked one of the nickel tabs right off the solder pads; obviously, I must now level up my soldering game.

Scraping the yellow silicone filter off the PCB reveals the minuscule LEDs:

Destroyed COB LED - excavated yellow silicone
Destroyed COB LED – excavated yellow silicone

You’ll recall they’re arranged in three series sets of six:

Circular 12V COB 18 LED panel - copper layout
Circular 12V COB 18 LED panel – copper layout

Some probing revealed five of six LEDs in one set was still functional:

Although a few other LEDs across the PCB survived, that’s not the way to bet when you run so much current through the poor things.

Ah, well, that’s why I always buy a few more parts than I really need …

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  1. #1 by Keith Ward on 2019-03-03 - 08:40

    Oops. It’s the brightest they’ll ever be … but only once.

    • #2 by Ed on 2019-03-03 - 09:37

      Live hard, die young!