My mousetrap killed my multimeter - can I fix it? - Page 1
Forum section: electronics / repair

author: macalla
author_rank: Contributor
timestamp: July 17, 2025, 08:19:13 pm
content: I wasn't thinking and tried to measure the voltage on the plates of an electronic mousetrap. No sparks or other drama but the meter immediately stopped working. Doesn't even turn on.Turns out the trap puts out 6kv. Meter says 1kV DC max.Wondering if I can find and fix what blew without too much trouble. I kinda like the meter so don't want to give up too soon. Its a Cen-tech from Harbor freight that I've had for many years. I see they still sell exactly the same unit which might mean it doesn't suck too bad, so might be even more reason to try to fix it.Fuse isn't blown. Have not checked anything else yet.Can anyone suggest which components to focus on? I know its hard without a schematic but maybe someone out there has some insight.If this is a fool's errand because the chips under epoxy are likely shot, I need to hear that too so I dont waste time messing with it.Here are a couple picsThanks!

author: wraper
author_rank: Unknown
timestamp: July 17, 2025, 08:28:58 pm
content: 99% chance at least one of the blob ICs died. The only way to fix it is if only blob on the right side died and one on the left is still OK, and you find what it is and solder packaged version after removing the blob. EDIT: apparently it's FS9721-LP3https://www.eevblog.com/forum/projects/mastech-ms8229-rs232-hack/

author: Kean
author_rank: Unknown
timestamp: July 17, 2025, 09:53:18 pm
content: Agreed. Almost certainly the blob ICs are kaput!There appears to be very little protection components (a few hidden below the fuse?), and if the protection components did their job (sacrificing themselves) then you'd expect the DMM to still power on but maybe give some incorrect readings.

author: calzap
author_rank: Frequent Contributor
timestamp: July 17, 2025, 10:15:00 pm
content: Meter is probably toast. It’s about US$60 on Amazon, more from Harbor Freight. In the same price range, you can get a name-brand like Klein or Instek. I did something similar years ago. Tried to test a cattle prod with a Beckman DMM. I sent it to Beckman, and they fixed it.Mike

author: Analog Kid
author_rank: Super Contributor
timestamp: July 17, 2025, 10:44:35 pm
content: And maybe next time use a high-R voltage divider and multiply the DMM value by the division factor.

author: macalla
author_rank: Contributor
timestamp: July 17, 2025, 11:15:23 pm
content: thanks for the input and the IC tip.There are these 4 fat diodes under the fuse, but they don't seem to be in the path of the voltage lead.

author: Zenith
author_rank: Frequent Contributor
timestamp: July 17, 2025, 11:16:08 pm
content: What's the problem to be solved? Is it catching mice or have you been seduced by technology? If it's catching mice I can recommend The Little Nipper. If you have a lot of mice to deal with there are low tech solutions based on a rod the mice or rats have to walk along to reach the prize of peanut butter. It's almost impossible and they end up drowned. You could also get a cat. Possibly, being technologically inclined, you could make a robot cat. You'd only have to charge it, no messing about with salmon/rabbit/tuna flavoured cat food. It could have emergent properties. Think Frankenstein. Snakes can be very efficient rodent killers, although they are not without maintenance problems. A robot snake I can see would involve obvious challenges.As you may gather, I don't have much patience with this particular problem.

author: macalla
author_rank: Contributor
timestamp: July 17, 2025, 11:18:54 pm
content: i trace the input path right to the ic, just like the data sheet says

author: macalla
author_rank: Contributor
timestamp: July 17, 2025, 11:20:45 pm
content: so i guess its toasted.Oh well that was dumb