Multimeter question damaged or not - Page 1
Forum section: electronics / beginners

author: Kantilo
author_rank: Contributor
timestamp: August 20, 2021, 11:55:07 am
content: Hello, I did a multimeter continuity test, but afterwards I wanted to measure the voltage on 5V, except that I was in continuity / resistance test, do you think that it could have damaged the multimeter? Thank you

author: HB9EVI
author_rank: Frequent Contributor
timestamp: August 20, 2021, 12:23:34 pm
content: well, if continuity test isn't working anymore now - then yes, it probably got damaged. if it still works, it's all okthat simple

author: rsjsouza
author_rank: Super Contributor
timestamp: August 20, 2021, 01:45:06 pm
content: If the multimeter has decent input protection, you could have plugged it into an outlet and have zero damage. Just out of curiosity, what is the brand/model?

author: calzap
author_rank: Frequent Contributor
timestamp: August 20, 2021, 02:53:58 pm
content: If it does not appear to be working, check the fuse(s) first.Mike in California

author: elekorsi
author_rank: Regular Contributor
timestamp: August 20, 2021, 06:20:15 pm
content: If it was damaged on 5V, then it is one truly crappy multimeter...Fluke survives 230V on continuity... proved

author: David Hess
author_rank: Super Contributor
timestamp: August 21, 2021, 01:00:52 am
content: The way ohms/continuity works is to measure in DC volts mode, which has considerable input protection, with an "ohms converter" in parallel with the input which amounts to a current source of typically 1 milliamp or less. The ohm converter is also protected, typically to a level of about 150 volts, so applying 5 volts in ohms/continuity mode should result in no damage.Since the current source can operate with considerable resistance in series with its output, old multimeters often used a very small 120 volt light bulb in series with the ohm converter output. This is effectively a very fast 120 volt PTC fuse.

author: Kantilo
author_rank: Contributor
timestamp: August 22, 2021, 12:43:59 am
content: Hello, thank you for taking the time to answer me, it was a Brymen 235, and finally, in the case where I do a voltage test, the positive tip being in the positive of a Jack DC jack (5V also) and that without doing it on purpose I touch with the negative piece of the multimeter does it damage it? He displayed 0V when i shorted the tipsThank you

author: Nusa
author_rank: Super Contributor
timestamp: August 22, 2021, 02:34:06 am
content: Quote from: calzap on August 20, 2021, 02:53:58 pmMultimeter fuses only apply to the current ranges, as a rule. Remove them entirely, and all the other ranges should still work.

author: bdunham7
author_rank: Super Contributor
timestamp: August 22, 2021, 03:13:36 am
content: Quote from: Kantilo on August 22, 2021, 12:43:59 amIt would be impossible to damage that multimeter doing that unless it was broken already. The only way you could to anything to it with a 5 volt supply is if you had the leads in the current jacks--and then you would only blow a fuse.

author: David Hess
author_rank: Super Contributor
timestamp: August 23, 2021, 03:17:57 am
content: Quote from: Nusa on August 22, 2021, 02:34:06 amThe ohms converter might be protected by a fuse. It is protected by something.

author: Nusa
author_rank: Super Contributor
timestamp: August 23, 2021, 05:27:19 am
content: Quote from: David Hess on August 23, 2021, 03:17:57 amSure, on good multimeters there will be input protection components for all the ranges, but I've never seen actual replaceable fuses used for anything but current ranges. Feel free to throw out an example that breaks the rule, if you know of one. Doesn't change the general rule, of course.On bad multimeters, there may be nothing between the input and the processor pin.

author: james_s
author_rank: Super Contributor
timestamp: August 23, 2021, 05:37:09 am
content: Well whether likely or not, I'd say the first thing to do is check the fuses, if they're good and it still doesn't work then check elsewhere. Also confirm that the battery is good, I've never used a Brymen meter but I've seen others malfunction when the battery was low.

author: magic
author_rank: Super Contributor
timestamp: August 23, 2021, 06:24:57 am
content: Quote from: Nusa on August 23, 2021, 05:27:19 amUni-t meters load the input with 220kΩ IIRC in thermocouple mode to produce ambient temperature reading if no probe is connected. This resistor is placed behind the mA range fuse, resulting in some truly mystifying behavior when the fuse is blown and the input flaps around in the breeze.

author: joeqsmith
author_rank: Super Contributor
timestamp: August 23, 2021, 11:39:07 am
content: Quote from: Kantilo on August 20, 2021, 11:55:07 amNoQuote from: Kantilo on August 22, 2021, 12:43:59 amThe Brymen BM235 is a very robust meter. I have one that I have exposed to much more harsh conditions than a 5VDC supply and have not damaged it. If you ever do damage it, be sure and post what you did. It should be a pretty funny story...Quote from: David Hess on August 23, 2021, 03:17:57 amI have seen a few low end meters that have placed the fuses in series with the functions other than current. The ones I have seen do not have a dedicated mA/uA input. The BM235 is indeed protected but not by a fuse.

author: BeBuLamar
author_rank: Super Contributor
timestamp: August 23, 2021, 01:24:15 pm
content: Quote from: Kantilo on August 22, 2021, 12:43:59 amSo does it still work or not?

author: David Hess
author_rank: Super Contributor
timestamp: August 23, 2021, 08:17:37 pm
content: Quote from: Nusa on August 23, 2021, 05:27:19 amI agree. Below are some easy to access examples that I had available.The first shows the Tektronix DM502 which uses a 120 volt lamp to protect the ohms converter. It was intended to be user replaceable with a soldering iron but that would not likely be the case today. Tektronix used fuse clips to hold the bulb in place.The second shows the stock condition of a Tektronix DM501 which uses an actual 250 volt 1/16th amp glass cartridge fuse to protect the ohms converter. The third shows a DM501 where the fuse was blown and I replaced it with a pair of 28 volt grain-of-wheat bulbs in series because I had them immediately available and the proper fuse is not cheap. Those diodes are part of the protection for the ohms converter and once I pulled them to verify that they were not damaged, I elected to reinstall them and associated parts in collet socket pins.