LED Strip lights flashing like a bad 90s rave - Page 1
Forum section: electronics / repair

author: Grytpype
author_rank: Contributor
timestamp: April 28, 2024, 11:18:29 am
content: Hi All, Hope you're all well!My LED strip lighting just decided to crap out and now, very consistently, strobe as per the attached gif.The components inside the power supply all look fairly straight-forward to me bar the SMD led driver (BP3319MB) on the bottom-side of the PCB.I swapped out the SIF10N65C mosfet in a straw-clutching moment with a near-as-damn-it equivalent but the disco continues. The caps all measure ok and I can't see anything else obvious.Anyone have any experience / ideas on what this could be? They're not expensive to replace but feels like this could be something fixable.Thanks in advance!

author: RoGeorge
author_rank: Super Contributor
timestamp: April 28, 2024, 12:01:26 pm
content: I would disconnect the LED strip and check the (group of) LEDs individually, one by one, with a DMM or with a voltage source + series resistor + 2 wires. Could be that one of the many series LEDs is defective (interrupted) and when the voltage across it becomes too high, it short-circuit itself and lights up the rest of the strip, but at a higher voltage than it should, then the overcurrent protection turns all off, and the flicker repeats just as the defective LED would be the starter in a fluorescent tube lamp.If not, then maybe check for dried out electrolytic capacitors in the power supply (though, they all look OK in the picture).

author: artag
author_rank: Super Contributor
timestamp: April 28, 2024, 12:55:25 pm
content: It looks like classic behaviour from a faulty or overloaded switching power supply - it starts, overloads, shuts off and after a short delay restarts. I wouldn't like to speculate why it's doing that but I'd start with that assumption.Unfortunately switching power supplies are quite hard to work on as at least half the active circuitry is operating at mains voltage. Unless you have previous experience of them or want - very carefully - to use it as a learning experience with possible destruction of the whole setup, the easy way out is probably to replace the packaged power supply.Nothing wrong with RoGeorge's suggestion and it might be a good (and cheap to try) start but it seems less likely than a power supply fault.

author: Grytpype
author_rank: Contributor
timestamp: April 28, 2024, 01:41:49 pm
content: Thank you both for the advice. I'll check the LEDs first and carefully pick through the high-voltage side if I'm feeling brave enough.

author: fmashockie
author_rank: Frequent Contributor
timestamp: April 28, 2024, 05:43:32 pm
content: I would be looking at IC1 or the BP3319MB LED controller. Not yet for replacement, but for testing. I have attached the datasheet for the BP3319MB. It provides a bunch of information on how the controller works. You can use this information to test the BP3319MB. Is it in undervoltage or overvoltage lockout? Is the PWM providing the correct frequency/waveform? You can verify all this by probing the IC with a DMM and scope.Now as someone else mentioned, the LED controller is on the primary side. And with it being a PFC controller, there could be voltage as high as 400VDC across the large filter cap. Therefore, it would be best if you used an active probe to check this IC with a scope. A high voltage differential probe like the Micsig DP10007 is affordable and works great.I would also recommend (like someone else mentioned) testing the led strip without the driver. You can hook it up to a DC power supply.

author: floobydust
author_rank: Super Contributor
timestamp: April 28, 2024, 06:58:23 pm
content: If the LED string goes open-circuit, due to thermal expansion on the bonding wires/die attach, the PSU output voltage can rise up - and when the LED cools off and reconnects, the filter caps discharge hard into the string. So, I have seen blinking LED strings with many failed elements when I was thinking it would be just one LED failing.The small capacitor by J3 is critical for the SMPS IC"s operation. Make sure its ESR is good as well as capacitance. These are 22-47uF 50V parts.

author: Grytpype
author_rank: Contributor
timestamp: May 01, 2024, 05:01:43 pm
content: Thanks all!...I did measure the DC output (without load) and get a saw-wave which I'm assuming should be pretty constant. It does appear to be in sync with the LEDs going on and off. I'll try and wire them up separately asap to check they're okay as per the above.Cheers!