Extech Power Supply Repair 382275 - Page 1
Forum section: electronics / repair

author: cinetron
author_rank: Contributor
timestamp: March 16, 2017, 08:03:11 pm
content: I have a dead Extech 382275 power supply. This is a switching supply 0 - 30 volts 20 amps. I took the housing apart and there is a fuse inside that can only be replaced by removing components. It's tucked between a large capacitor and a heatsink. It is seen in the attached photo. The capacitors are about 2.25" tall. I have a couple questions.Has anyone had luck replacing the fuse without removing a capacitor. Seems like a crazy place to put a fuse?Anyone know why the fuse would typically blow? I thought the supply was short circuit protected ie. would shut off the output under a short circuit condition? I tried calling their tech support but the person answering didn't know how the short circuit protection worked?? When the fuse blew I had set the current limit at 8 amps so I thought that meant it would only supply 8 amps, not blow a fuse, especially since it is rated at 20 Amps? If anyone has experience with this supply I would really appreciate hearing from you.Thanks

author: singapol
author_rank: Frequent Contributor
timestamp: March 17, 2017, 01:58:55 am
content: Something is seriously wrong if a 20A fuse blows unless you are naive to think it's due to aging which is possible.Anyway a 20A fuse does not cost much?

author: cinetron
author_rank: Contributor
timestamp: March 17, 2017, 03:57:03 am
content: I was able to wiggle the fuse out. Turns out to be an 8A 250V fuse that blew so it must be on the high voltage side. I ordered a new fuse so will see if I can wiggle it back in without having to remove the cap.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 17, 2017, 12:24:10 pm
content: There is usually more wrong if the fuse blows. There is a small chance during turn on to just blow the fuse from the inrush spike, but during operation, even with a short there likely is another fault.Before adding a new fuse, I suggest checking the rectifier and maybe diodes on the secondary side. The typical failure mode of diodes is a dead short and this can usually be measured in circuit. One could also test the power MOSFETs the same way - if broken the usual way is a short D to source.The supply is supposed to be short circuit proof. So the defect might even be under warranty.

author: cinetron
author_rank: Contributor
timestamp: March 17, 2017, 02:47:01 pm
content: Thanks a lot for the suggestions. Unfortuneately I dont have a schematic and there is a lot packed in there . Extech wont give me a schematic either and warranty is over. Maybe with some digging I can figure out whats what on the board.

author: cinetron
author_rank: Contributor
timestamp: March 22, 2017, 06:53:50 am
content: I tried changing this fuse and it blew again with nothing on the output. There must be something else wrong with it besides just a blown fuse. Wondering if anyone has sent something to Extech for repair in the past. I am in Canada so I'm sure the shipping back and forth and repair could be costly since it is no longer under warranty. Unfortunately Extech can't give me any idea of repair cost unless I send it to them. Any advice on how to get this repaired in a reasonably cost effective way. Is there any way to get schematics for this in which case I would attempt to repair it myself? Thanks

author: tomtechtod
author_rank: Newbie
timestamp: July 05, 2020, 06:33:01 pm
content: Know it's an old topic, but had the same issue, other people might have the same problem.DCDC converter output diodes were toast in my case.Model MBR20200ct schottky diodesThat's D14 D16 mounted on a heatsink, 2x TO220 packages.Replaced fuse and these two diodes. Unit works.