Strobe light repair (Working but squealing and RF noise) - Page 1
Forum section: electronics / repair

author: cbassett1000
author_rank: Contributor
timestamp: September 02, 2019, 09:31:40 pm
content: I have a Whelen talon (vehicle strobe light) that I've had for years. It has always squealed, and always had bad RF noise (don't know if the noise is going through the air or backfeeding through the DC power cord) It interferes with the two way radios in the vehicle especially around the 150 MHz band. The audible squeal I've pinpointed to what appears to be the 4 capacitors on the right. In the picture, the circuit is repeated twice (other not shown) , one for each lighthead. The other "cap farm" on the opposite lighthead (not shown) makes noise as well but not as audible. EDIT: This runs on 12 volts DC as board input. The light heads are LED.I would recap it but I don't want to do it if the issue is a design flaw and will not solve the issue. All components are on a single side though it is a 1+ layer board. I'm sure I'm not the only one to have an issue, as Whelen completely revamped the board in later revisions of the product. (I'm talking square one redesign, completely different components, just everything) The audible squeal is bearable, the RF noise generated is not. Any solutions or comments?

author: cbassett1000
author_rank: Contributor
timestamp: September 05, 2019, 08:36:40 am
content: I have made a crude EMI detector and came to the conclusion that 7/10 EMI is being generated at the inductor closest to the LM. The other 3/10 seems to come from a combo of the LM and the cap farm. The inverse is true regarding audible noise. Mostly coming from the cap farm (audible) with a small amount from the inductor. I can't quite tell what value those caps are from the datasheet, the prefix or decimal. Again any help on any of this is appreciated.

author: fzabkar
author_rank: Super Contributor
timestamp: September 05, 2019, 11:03:58 pm
content: https://au.mouser.com/pdfdocs/NichiconUDcapacitors.pdf33uF, 50V

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 06, 2019, 11:06:51 am
content: Is that the only board in it? It doesn't look like quite enough for a strobe, but maybe just enough for fixed strobe rate into a panel of LEDs.You say it's 1+ layers, but how many is it? What's on the back side?If nothing else, you can put everything inside a metal box (potentially including metal screen for the light) and put a line filter where the power lines pass. If the board doesn't have ground planes, it's basically futile to try and address it there.Tim

author: cbassett1000
author_rank: Contributor
timestamp: September 09, 2019, 05:46:53 am
content: First of all, thanks fzabkar, I thought that is what it is but wanted to be sure.Tim, it is just the one board, this a small module (you can Google Whelen talon) that fits in your hand that weighs no more then a couple of kilos, if that.It powers two LED modules. Strobe is more the generic term in my industry. What I mean by 1+ is I can confirm at least 2 layers. On the backside is mostly ground with a positive trace going to LED circuit B. Simply put, the 12V goes into a "section" that does whatever to it (appears to be pattern and sync controlling) then it 2 outputs lead to each specific LED circuit, shown above, then outed to its respective LED module. Metal box, (unless basic aluminum foil inside but even then the components definitely get warm), is undesirable due to asthetics, and the need for high visibility.I am currently going to try the line filter option and see how it goes. The audible and the RF noise are mostly likely in each LED circuit, as they make different noises depending on which LED is active. (LED refers to a six string LED module)Any other suggestions please post!Thanks!