LED car light with MC34063AL - Page 1
Forum section: electronics / repair

author: angrest
author_rank: Newbie
timestamp: July 22, 2014, 08:19:51 pm
content: Hi, I have issue with LED light for car. There are 4 white LEDs and MC34063AL circuit. Problem is, it's not working. It's rated 12V/4.8W. If i put voltage of 4V on input, it draws about 700 mA, and the IC package becomes quite hot. Also capacitors and inductors are quite warm. LED diodes are all off (they are OK, I checked them with low voltage directly on their terminals). I have only multimeter, no scope. Any ideas? Thanks.I attached the image of the PCB.

author: corrado33
author_rank: Frequent Contributor
timestamp: July 22, 2014, 08:49:08 pm
content: If everything is getting hot, then there's a short somewhere. Look around for shorted traces. Check resistance between the power and ground leads or between traces that shouldn't be connected. Remove (Desolder) the IC and check again. It looks like that board is beat to crap (from the pictures at least). Has someone already tried to repair it? It looks pretty simple, shouldn't be that hard to fix.

author: angrest
author_rank: Newbie
timestamp: July 22, 2014, 10:21:52 pm
content: I checked components for short circuit... Leads of one of the capactitors were short circuited. I removed the capacitor, checked it, but it was OK, at least my multimeter shows correct capacitance. I measured pads on PCB and they are short circuited.But, I tried to power the board without that cap and it started to work! I don't understand why. It blinks a little in the beginning, but after a while LEDs are on and don't blink. Don't know if it glows with full brightness since it draws only about 100mA @ 12V. I think it should draw more current. I also tried to add different cap (while powered on), but it immediately does the same thing - LEDs go off and it starts to drain high current.

author: corrado33
author_rank: Frequent Contributor
timestamp: July 25, 2014, 05:18:56 pm
content: If I were you, I'd trace those capacitor pads to find out why they're short circuited. That'll probably lead you to the root of your problem.

author: Monittosan
author_rank: Regular Contributor
timestamp: July 27, 2014, 03:55:39 pm
content: Is that from a DRL?

author: rob77
author_rank: Super Contributor
timestamp: July 27, 2014, 05:19:02 pm
content: i wouldn't put that one on my car... no way... seems it has zero protection against transients => it's a matter of time when and how it blows up.

author: dannyf
author_rank: Super Contributor
timestamp: July 27, 2014, 08:38:03 pm
content: QuoteWhy wouldn't you run it at 12V if it is rated at such?

author: AndyC_772
author_rank: Super Contributor
timestamp: July 27, 2014, 09:00:38 pm
content: I agree. If you're running it at a voltage that's lower than what it's designed for, then if it's a switched mode power supply, it'll draw proportionately more current to compensate.If you run a 12V device at 4V, there's a good possibility it'll draw 3x the current, which equates to 9x the I2R heating. No wonder it gets hot.

author: senso
author_rank: Frequent Contributor
timestamp: July 28, 2014, 12:15:58 am
content: No heatsinking for the leds, the back is even exposed with holes in the pcb

author: Richard Head
author_rank: Frequent Contributor
timestamp: July 28, 2014, 09:00:58 am
content: Why wouldn't you run it at 12V if it is rated at such?Here's why.

author: rob77
author_rank: Super Contributor
timestamp: July 28, 2014, 09:25:21 am
content: Quote from: Richard Head on July 28, 2014, 09:00:58 amand that's why i posted this:Quote from: rob77 on July 27, 2014, 05:19:02 pmall those cheap car LED strips are just a piece of shit not suitable for automotive applicationtrying to run it @ 4V instead of 12V will not make it any better (it's even worse)... running at whatever voltage will not enhance it => it's still the same piece of shit.sorry for the strong language, but seeing someone burning down his car because of installing some shitty $2 led strip (which is not approved light source and it's illegal in many countries) makes me angry....

author: djococaud
author_rank: Regular Contributor
timestamp: July 29, 2014, 06:13:59 am
content: Quote from: senso on July 28, 2014, 12:15:58 amI thought the same before I saw the remains of thermal grease on the back of the LEDs. I think this PCB is meant to be fixed to an heatsink (with metal bits touching the back of the LEDs) O0

author: Mr Smiley
author_rank: Frequent Contributor
timestamp: July 29, 2014, 04:39:33 pm
content: Remove the chip and measure for a short between pins 1 and 2, if so the chip's buggered