What could this circuit be (I damaged it)? - Page 1
Forum section: electronics / beginners

author: 240RS
author_rank: Regular Contributor
timestamp: August 13, 2023, 05:14:04 pm
content: I damaged the circuit on the bottom left of this microcontroller based development board and have no idea what kind of circuit it is. I do not have schematic.The 4k7 marked component is an inductor, right? The 6 lead chip right of it has a marking that looks like 8ARM or 8ARU. Opamp maybe?And the components I knocked off (tried to slide it into something) are those resistors, or can capacitors be that small also?Any ideas?Thanks!

author: homebrew
author_rank: Frequent Contributor
timestamp: August 13, 2023, 05:34:21 pm
content: Right, that is a 4.7uH inductor. As it is near the 5V input with the input selector jumper, it looks like a switch mode voltage regulator. The lite chip will be the controller, regulating the output voltage. The broken off components are most likely capacitors. I would try to identify the controller chip and look up its data sheet. You would most likely find a similar schematic there.Do you have a microscope or a good magnification lens?Also, if this is a development board, you'll most likely find a schematic online from the vendor.

author: RoGeorge
author_rank: Super Contributor
timestamp: August 13, 2023, 05:42:00 pm
content: In that area is a SMPS (Swithing-Mode Power Supply) power supply, most probably from 5 to 3.3V.That IC is the voltage stabilizer. The 4k7 is a coil, indeed. In the same area it is expected to have some resistors (usually black), some capacitors (usually brown), a Schottky diode (also black but usually thicker than an R).From the picture is not possible to distinguish what or if something is missing.Try taking a clear picture, with the components in focus.

author: 240RS
author_rank: Regular Contributor
timestamp: August 13, 2023, 08:35:43 pm
content: Aha! SMPS. Won’t work without it then… but also, not too difficult to repair.The schematic is not available, but of the SOM on the board there is. I will check for voltage levels.Making better pictures is hard. Will try again tomorrow.

author: andru123
author_rank: Newbie
timestamp: August 13, 2023, 08:39:38 pm
content: If you cannot even make a focused foto, how are you even going to solder it back?The circuit with 3 legs is the most important, once you figure what it is, there is usually a ref design with all other components around.

author: 240RS
author_rank: Regular Contributor
timestamp: August 13, 2023, 08:46:45 pm
content: I think I cannot solder that indeed.Checked the SOM: 3.3V indeed.Will contact the vendor. Worst case I will add my own 3.3V supply.

author: Manul
author_rank: Super Contributor
timestamp: August 13, 2023, 08:51:30 pm
content: In case you will try to repair or check voltages, I strongly suggest that you temporarily cut the output trace, until you repaired it and you are sure that the voltage is correct. A broken buck converter might output 5V into 3V3 rail.If you know that 3V3 rail current is small, you can also repair the board by putting in a linear regulator instead.

author: Shonky
author_rank: Frequent Contributor
timestamp: August 13, 2023, 09:18:19 pm
content: Small note: The 4k7 is actually 4R7 = 4.7uH (as noted) on an inductor.