K-50 Switching Mode Power Supply repair - Page 1
Forum section: electronics / repair

author: titch2k6
author_rank: Newbie
timestamp: July 02, 2024, 04:20:48 pm
content: We have an Ibiza Light DJLight65 unit that has a K-50 Switching Mode power supply (SMPS) fitted internally. This unit has an onboard PCB fuse. Last week, we had a power surge due to a lightning storm and the internal "fuse" blew.Taking the unit apart and looking at the power board, the item blown is obvious. However, we are struggling to identify the F3A device used. We believe it to be a fusible resistor, but the colours are a bit off to make them out clearly. We believe it is a 27R (red, violet, black) with a 3% tolerance (orange). Does this sound about right? If so, that leads us to the second issue.....We just can't find a 27R 3% fusible resistor anywhereThere are plenty of 27R 5% (gold band) around, which makes us wonder if the band is actually supposed to be gold and not orange. This then leads us to the question of what wattage this would be - 0.5W, 1W or 2W, if not higher.We have tried searching for information/schematics for the Chinese-made K-50 unit and surprise surprise - nothing can be found online. So, thought we would ask people with a bit more knowledge in these things and hence, why we are posting here.Can anyone confirm i) that this is indeed a fusible resistor as opposed to a High Voltage resistor or a Power Surge resistor; ii) It is indeed rated at 27R; iii) What we could replace it with (UK purchase) to get the unit working again?Pictures are added below for visual reference. SMPS data is as follows:Input: 230VAC 50/60Hz 1AOutput: 10.5V (11VDC max) 4.5AUsed for LED modules onlyMany thanks in advance for any useful assistance anyone can give.

author: m k
author_rank: Super Contributor
timestamp: July 14, 2024, 05:48:15 pm
content: Is it a mains fuse?Seems to be.So 3 0 00 from the other end.

author: eblc1388
author_rank: Frequent Contributor
timestamp: July 14, 2024, 10:48:07 pm
content: I have noticed that parts on the board are given both a designation and component value, e.g. the inductor L1/10uH and L2...So unless there is another fuse F3B somewhere on the board, I would say with certainty that the part is a fuse of 3A rating.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: July 14, 2024, 11:00:14 pm
content: HiI would be very surprised if the fusible resistor is the only problem, you have a 99% chance of just destroying the replacement.G Edmonds

author: wraper
author_rank: Unknown
timestamp: July 14, 2024, 11:08:14 pm
content: QuoteHow do you see two nearly identical rings as two very different colors?And it's certainly not violet.That's a 22 ohm fusible resistor. Orange ring has nothing to do with with resistance or tolerance. It's a manufacturer specific thing, usually type marking. Common mode choke looks dodgy, as if there is a short between wires. Although photo is too blurry, cannot say for sure.

author: bastl_r
author_rank: Regular Contributor
timestamp: July 15, 2024, 12:48:20 am
content: If you replace the resistor, every new one will burn again!Look on the inductor nearby. There is the short that wil let the resistor burn