ARGB PC fan died plugging in reverse polarity WS2812B LED strip, why? - Page 1
Forum section: electronics / beginners

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: July 19, 2022, 05:09:24 am
content: I have an ARGB (Addressable RGB) PC fan plugged into an ARGB controller on my test bench (it has an 18-LED strip inside). I got a new WS2812B ARGB LED strip from Aliexpress today, which has a JST female connector. The controller has JST male connectors on it, so I plugged it in and flipped the power on. Neither the fan RGB nor the strip come on. I touched the controller and it was unusually warm. I measured voltage on the actual pins and discovered the controller is wired backwards from the new LED strip I got, +5V and GND were reversed. The controller has all-black wires, which is why it wasn't visually obvious the polarity is wrong. I used some jumper wires and reversed the polarity, to discover the controller is fine, the new LED strip is fine, but the fan has died and none of the LEDs so much as blinks or flickers. I've plugged it into my PC's RGB controller to verify it is indeed, toast.This is odd to me. I could understand if the controller died, because it's the power source. I could understand if the LED strip died because it's the device experiencing reverse polarity. The fan never experienced reverse polarity, so I can't really think of why the fan would die. Even if the reversed polarity caused the data line to be pulled up or down, I wouldn't think that would hurt the fan data input. Why would the fan be the only casualty while the others survived?

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: July 21, 2022, 12:02:49 am
content: Pluging the diode strip in backward would do nothing.Fan failure was proably timing as in bad timing.Jeff

author: ozcar
author_rank: Frequent Contributor
timestamp: July 21, 2022, 03:45:06 am
content: Quote from: Jeff eelcr on July 21, 2022, 12:02:49 amI would expect that to be true if they really do use WS2812B LEDs as stated. For other LEDs, I would not be so sure.For ordinary RGB LEDs, they would be reasonably protected due to them being, well, diodes, and the strips typically consist of nothing more than the LEDs and series resistors. However these are pixel LED strips and the controlling ICs might not take kindly to reverse polarity.Genuine WS2812B LEDs should be OK, as reverse polarity protection is a stated feature/advantage compared to some other parts like the older WS2812. Pixel strips also have capacitors on them but I'd guess those would not be polarised (100nF recommended).In any event, it seems that the strip that failed was not reverse connected. Something evidently was drawing more current as the controller was overheating. Perhaps the offending strip was unplugged with the power still on, and that somehow caused the power supply to misbehave?Whatever the cause, it might be worth investigating the failed strip a bit more. If the failure was due to something on the power lines, then more than one of the LEDs could now be toast, but if it was something on the data line, it might have killed only the first LED (the others won't turn on if the first one is not passing the signal on). If nothing else, cutting the first LED off and connecting to the next LED might reveal something.

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: July 23, 2022, 12:32:23 am
content: I don't think I unplugged the strip with the power still on, I feel like I shut it off at the PSU hard power switch, but I've slept since then so I could be remembering wrong. It was an ATX PSU, so I wouldn't think it would misbehave, but anything is possible.I'll have to see if I can pull the fan apart and get to the LED strip inside. There are no visible screws or fasteners, just a seam that appears to be very tight with no give, so it's likely one of those solvent-welded together things that can't be easily taken apart without destroying it.

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: July 23, 2022, 07:20:42 am
content: Started trying to pry the fan frame open, but it wouldn't budge, not even a little bit. Seemed to be tightest in the corners, so I tried pulling off the rubber isolators and was a bit surprised to find screws. Once I got those out, the frame separated easily into two halves revealing a custom 5050 LED ARGB strip made of a semi-rigid plastic-like material. I almost expected to find a generic cuttable one. I noticed the strip has an unused solder pad labeled OUT. That would have been nice if they'd wired it up so additional fans could be daisy-chained. Shame they didn't, I would have been willing to pay the cost difference.I measured resistances across the LED pins, and the first one was different from the rest, it had about 90k ohms across its Data In and Data Out pins while the rest were double that. I then jumpered across the first LED's DI and DO pins while connected to the controller, which actually got 3 of the next LEDs to slowly light up in sequence and stop. I figured you are right, @ozcar, first LED seems to be toast, and somehow interfering with the data signal. Since the strip isn't a generic cuttable one, I desoldered the first LED and soldered a tiny jumper across DI and DO. Plugged it into the controller, and now the rest of them work. I've reassembled the fan, it has a slightly dimmer spot now with the missing LED, but doesn't look too bad. I may replace someday if I end up with an extra from shortening an ARGB strip.Still not sure what would have killed that first LED. DI pin must have just gotten something it really didn't like.