SMPS Ground Question and Power Supply Substitution - Page 1
Forum section: electronics / beginners

author: Adam60
author_rank: Regular Contributor
timestamp: January 27, 2016, 05:01:14 am
content: Good Evening,This is my first post here and it is a couple of simple questions which I think I know the answers to, but just want to be sure. When I am testing mains voltage on the primary side of the transformer, my black lead will go to the neutral wire, correct? When testing the secondary side, I can place my negative DMM lead on the negative side of the large cap to get all my DC voltages, correct? Is there ever a time when this would not be true?My second question is this. I am new to SMPS but I have one here that the secondary side is dead. Primary side and fuse are okay. If I were to remove the transformer, could I hook my power supply up to the secondary side and slowly crank up the voltage and watch for overheating components? Is there a better way to find the dead component on the secondary side? This is a small SMART CHARGER type SMPS. Any help is appreciated.Thank you for helping a NEWB.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 27, 2016, 06:11:27 am
content: Yes.The only time you can't touch the probes wherever, is if the meter itself is grounded somehow (which should never be the case; it should always be nicely wrapped in thick plastic like it is), or if it's set to a current range (in which case, you'll probablyand feel dumb).SMPS can usually be powered up externally from the output side, but do some work with the meter first. Does the diode test read anything on the output terminals? Does it look like a short circuit? If so, it's probably best not to connect a power supply to it, because you'll probably just short it out in the process.And if it's a charger, designed for direct charging, then the output terminals probably aren't even a basic SMPS, but a more complicated battery charger system, which will be watching for open and short circuit, precision voltages (under/over charged), delivering current or voltage... all manner of things not easily tested.Tim

author: Adam60
author_rank: Regular Contributor
timestamp: January 27, 2016, 08:13:57 pm
content: Thank you for your response but still left with questions. Where does the black probe go from my meter to test secondary side voltages. Is the large cap the best place or are there other places I need to move it to>?For the output, I believe I had around 170VDC on the output side of the rectifier. After that is a MOSFET but not sure how to test after that.

author: tautech
author_rank: Super Contributor
timestamp: January 27, 2016, 08:46:59 pm
content: Identify the SMPS controller, study its datasheet and you'll likely find the recommended "typical application" very similar to the circuit you have.

author: Adam60
author_rank: Regular Contributor
timestamp: January 28, 2016, 12:38:42 am
content: Looking further into this unit, I found what could possibly be a crack in the TINY13A Atmel Processor. What do you guys think? Do I need special equipment to diagnose/test/replace this component? How can I tell if it is defective?http://www.atmel.com/images/doc8126.pdf

author: tautech
author_rank: Super Contributor
timestamp: January 28, 2016, 08:10:23 am
content: Quote from: Adam60 on January 28, 2016, 12:38:42 amLooks more like a scratch to me.