First time multimeter user having few doubts, please help. - Page 1
Forum section: electronics / beginners

author: cikain
author_rank: Newbie
timestamp: June 24, 2023, 03:11:23 pm
content: Hello people,Recently I got a job as field computer technician, I have been told to buy a multimeter for troubleshooting laptops and desktop, e.g. motherboard, adaptor, I/O board, powesupply etc. I never used a multimeter before, I do know how it works but never used it, please clear few of my doubts on this subject.While measuring A/C current if I accidently put red probe on nutral and black probe on phase, will it be damaging my multimeter?While measuring D/C current if I accidently put red probe on - and black probe on +, will it be damaging my multimeter?also suggest me few multimeter models price range 10-25 USDfor laptop and desktop troubleshootingMaybe this is the stupidest question but I will ask anyways. Have a nice weekend guys.

author: David Hess
author_rank: Super Contributor
timestamp: June 24, 2023, 05:06:56 pm
content: Quote from: cikain on June 24, 2023, 03:11:23 pmIn both cases if you are lucky, then only the fuse inside the multimeter will blow.

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 24, 2023, 05:23:28 pm
content: A proper decent multimeter should handle both cases without damaging itself.

author: tunk
author_rank: Super Contributor
timestamp: June 24, 2023, 05:28:01 pm
content: Until you learn and get experience - do not measure current at all.As a computer technician, I would guess that you mostly will check voltages.

author: liaifat85
author_rank: Regular Contributor
timestamp: June 24, 2023, 05:44:22 pm
content: 1) Yes. It can.2) Yes in case of high voltage. In case of low voltage, No. You will see negative reading only.

author: cikain
author_rank: Newbie
timestamp: June 24, 2023, 05:55:23 pm
content: Thanks for the quick response guys, I really appreciate it, any suggestion for beginner friendly multimeter within price range of 10-25 USD

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: June 25, 2023, 02:06:25 am
content: Used or Harbor Freight.Jeff

author: rstofer
author_rank: Super Contributor
timestamp: June 25, 2023, 02:50:56 am
content: In the OP, we are all assuming that 'current' is properly used from an EE point of view. What if it is generically used and really means voltage in this context?I would grab a 9V battery and three resistors around 1,000, 1500 and 2200 Ohms and wire them in series with the battery.. Measure the battery voltage and work out mathematically what the voltage drop across each resistor should be. Measure the voltage across each resistor and compare with the calculated value.Now set the meter to measure current and insert the probes with the red probe to battery + and the black lead to the resistor string. Does the current make sense given the battery voltage and the sum of the resistor values?Due to tolerances for the resistors, the values won't match the math by some percentage.Now set the meter up to measure voltage - never leave it set to measure current.Make more complex resistor networks then calculate, measure, compare. Get used to handling the meter.One way or another, you have the break in to a circuit to measure current with a DMM. I almost never do this. It is usually easier to measure voltage.

author: liaifat85
author_rank: Regular Contributor
timestamp: June 25, 2023, 06:23:49 pm
content: Dave made a review on 25 Dollar ANENG AN8008 Multimeter:

author: BeBuLamar
author_rank: Super Contributor
timestamp: June 25, 2023, 10:35:27 pm
content: Quote from: cikain on June 24, 2023, 05:55:23 pmIt's an important tool for the job. Get a decent meter not a $25 one. Other people do look at your tools and judge your skill (although it's not fair but they do).

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 12:56:23 am
content: From 2019 to 2022 I helped out a friend with a computer shop (viral issues with staff) by fixing PCs and laptops. I had a power supply tester and a handful of universal laptop power supplies but that was it. No DMM, no soldering iron, no scope. The only other tools were hand tools. I fixed on average 2 PCs and 3 laptops a day for nearly 3 years. Never once did I require a DMM or any other instrument. In general, component level repair is not practical. Most people will not spend the money to pay the labor + parts to diagnose and repair a MB or a peripheral controller in this commodity driven business and you'll need a whole lot more than a DMM to do that kind of work. Scopes, logic analyzers, lab grade power supplies, at least 2 DMMs, SMD re-work station, temperature controlled soldering iron, a supply of solders, solder pastes, fluxes, etc., etc... and time the customer will need to pay for.That said, a $25 DMM will last about a week in the hands of a road tech.

author: mengfei
author_rank: Regular Contributor
timestamp: June 26, 2023, 01:05:49 am
content: the multimeter I use is a cheap Digital AUTO everything & has only 4 buttons, it will measure according to source, it was like $5(sale) only & palm size.

author: mwb1100
author_rank: Frequent Contributor
timestamp: June 26, 2023, 02:55:30 am
content: Fluke 101 goes for about $45 in the US - maybe it’s close to your price range in India? It doesn’t measure current. If you don’t need that (and many or most repair jobs don’t), then you won’t have the worry about having your probes set up incorrectly. And Joe Smith (who does a series of YouTube’s testing meter robustness) has found that the Fluke 101 is among the most robust meters he’s tested.If that doesn’t meet your needs the various inexpensive Aneng meters like the AN8009 have a good reputation for features, accuracy and value if not robustness. There are a ton of reviews of Aneng meters on the internet to help you decide.

author: mengfei
author_rank: Regular Contributor
timestamp: June 26, 2023, 03:30:38 am
content: oh, i think that's the brand that I have "Aneng" one, had for almost 2 years now

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 03:37:08 am
content: Quote from: mengfei on June 26, 2023, 03:30:38 amAnd do you use it to troubleshoot laptops and modern PCs?

author: mengfei
author_rank: Regular Contributor
timestamp: June 26, 2023, 06:20:18 am
content: oh yes I do, very useful & handy to check voltage & resistance on the fly without fiddling with a switch or button, it even has a NCV check.check them outhttps://aneng.en.alibaba.com/https://www.amazon.com/ANENG-Multimeter-Auto-Ranging-Rechargeable-Anti-Burning/dp/B0B9RBLCMH?th=1mine is the M118 if i'm not mistaken

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 06:26:28 am
content: Quote from: mengfei on June 26, 2023, 06:20:18 amMarvelous! And when you find a resistance out of spec (love to know where you get the schematics) or a voltage you don't like, what do you do?And that NCV. How does it help you with a 1.8V CPU supply in a laptop?Maybe take us through a "typical" laptop repair here.Eagerly awaiting

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 06:28:47 am
content: Quote from: mengfei on June 26, 2023, 06:20:18 amYou could look at it.

author: rstofer
author_rank: Super Contributor
timestamp: June 26, 2023, 09:24:47 am
content: That Aneng AN8008 (video above) will do just fine and if it walks away it wasn't much money. $26 at Amazon.I have a bunch of DMMs including a Fluke 189 but the Aneng is the one I use most often. It's just handy to have around.https://www.amazon.com/Multimeter-True-RMS-Digital-Accurately-Measures/dp/B08JLKD9MQ

author: EEVblog
author_rank: Unknown
timestamp: June 26, 2023, 10:30:58 am
content: Quote from: cikain on June 24, 2023, 03:11:23 pmIf you do this on the mains, you will blow the fuse and get a loud BANG. This is the worst possible thing you could do to a multimeter, it's BAD, don't do it.If you are lucky you will only blow the fuse and not destroy your meterIf you do it on a motherboard or other lower power power supply you could damage the product (and blow the fuse), but not particually dangerous.Well designed meters use ceramic HRC fuses to help prevent damage to the meter so only the fuse blows.Generally a $20 meter is going to be quite poor in this regard.If you want to prevent this happening by accident, get a meter that doesn't have a current range. In that case you can't reaklly damage the meter regardless of what you do to it.

author: Jwillis
author_rank: Super Contributor
timestamp: June 26, 2023, 10:52:39 am
content: Quote from: EEVblog on June 26, 2023, 10:30:58 amIt's important to understand what a meter has been rated for and to know whether or not the manufacturer is IEC compliant.https://www.digikey.ca/en/blog/what-are-multimeter-cat-safety-ratings

author: EEVblog
author_rank: Unknown
timestamp: June 26, 2023, 11:00:48 am
content: Quote from: Jwillis on June 26, 2023, 10:52:39 amBasically any meter under $50 doesn't have a proper rating, and certainly not independently tested.But the OP is testing motherboards and other low level electronics etc, so it's not really important.

author: EPAIII
author_rank: Super Contributor
timestamp: June 26, 2023, 11:05:11 am
content: Since AC is just that, AC or ALTERNATING current, the answer to your first question is NO.As for the second question, I would have to say that in the $10 to $25 USD range, the answer would depend a lot on the individual meter.In either case the most important precaution would be to be sure to have the largest current range selected BEFORE connecting the meter's leads. Then, if the reading is very low on the scale, you can switch to lower current scales for better resolution.In either case, current measurements, AC of DC are only needed in a very few and very rare situations. As a beginner, you should not worry about them. Or attempt them for some time to come.While I do have and use some very inexpensive meters, I would not recommend them for a total beginner. While learning it is a lot better to have a somewhat better meter which will be more forgiving of your mistakes. It also may be less expensive in the long run. Here are some that I would suggest:https://www.lowes.com/pd/IDEAL-ID-600-Volt-Manual-Multimeter/5000045533?cm_mmc=shp-_-c-_-prd-_-elc-_-ggl-_-LIA_ELC_106_Tools-Wire-Connectors-_-5000045533-_-local-_-0-_-0&gclid=Cj0KCQjw7uSkBhDGARIsAMCZNJt3nAX8WlZB5vvCS18US6Xqbs0dJXEo4IF5yiu5s-H_5gR82lMDqpsaAtyQEALw_wcB&gclsrc=aw.dshttps://www.amazon.com/Fluke-101-Multimeter-Equipment-Industrial/dp/B01IB9S6WK/ref=asc_df_B01IB9S6WK/?tag=hyprod-20&linkCode=df0&hvadid=309819400004&hvpos=&hvnetw=g&hvrand=17360206466362974401&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9027887&hvtargid=pla-489059322205&psc=1&tag=&ref=&adgrpid=60510211606&hvpone=&hvptwo=&hvadid=309819400004&hvpos=&hvnetw=g&hvrand=17360206466362974401&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9027887&hvtargid=pla-489059322205https://www.homedepot.com/p/Klein-Tools-600-Volt-Digital-Multi-Meter-Manual-Ranging-MM325/320822947?source=shoppingads&locale=en-US&&mtc=SHOPPING-RM-RMP-GGL-D27-027_011_TOOLS_ACC-PB-KLEIN_TOOLS_INC-NA-SMART-NA-NA-MK681362200-NA-NBR-1927-CON-NA-FY23_1927_RM2&cm_mmc=SHOPPING-RM-RMP-GGL-D27-027_011_TOOLS_ACC-PB-KLEIN_TOOLS_INC-NA-SMART-NA-NA-MK681362200-NA-NBR-1927-CON-NA-FY23_1927_RM2-71700000083602792-58700007073070013-92700063677501837&gclid=Cj0KCQjw7uSkBhDGARIsAMCZNJtls71Hsvnc-8JPp9OCeh95JA2_czBMnl2-vb8T7FN0a9zMNFLXBcIaArXfEALw_wcB&gclsrc=aw.dsThey are not terribly more than your suggested cost range but they are all CAT III rated so they do incorporate at least some basic protection against catastrophic failure that could result in a bad of lethal shock. And all of them are made by known companies so they will likely be constructed better in general.Finally here is one more that I would recommend if you can spend even a bit more. I recently purchased one of their better meters and am very satisfied with it. They have a very good combination of low cost and great features.https://brymenmeter.com/brymen-bm236r-multimeter.htmlQuote from: cikain on June 24, 2023, 03:11:23 pm

author: EPAIII
author_rank: Super Contributor
timestamp: June 26, 2023, 11:33:33 am
content: Err, NO. A $25 meter will last about a week in the hands of a beginner. In the hands of an experienced tech, it should last a lifetime.Quote from: BillyO on June 26, 2023, 12:56:23 am

author: BillyO
author_rank: Super Contributor
timestamp: June 26, 2023, 02:03:43 pm
content: Quote from: EPAIII on June 26, 2023, 11:33:33 amReally? Sure, whatever you say.Just one question, given the OP's questions, which category would you put him in?

author: ArdWar
author_rank: Frequent Contributor
timestamp: June 26, 2023, 03:25:36 pm
content: I'm not even sure if OP was asking about current measurement or the effect of putting the probe backward, or both. The way the question is worded put a lot of emphasis on the probe being "wrong colors on the wrong voltage".Measuring "AC current" is just common colloquialism for measuring AC in general, often for its voltage.

author: EEVblog
author_rank: Unknown
timestamp: June 27, 2023, 01:27:02 am
content: Quote from: ArdWar on June 26, 2023, 03:25:36 pmYes, it should be made clear that any multimeter can safely have the probes back to front, and can measure negative voltages and currents.It's tryign to measure voltage when the probes are connected the Amps current jack that is the problem.

author: trilerian
author_rank: Regular Contributor
timestamp: June 27, 2023, 04:17:44 am
content: Quote from: BillyO on June 26, 2023, 12:56:23 amI'm going to agree with the above post. I have been in IT for the last 12 years. I started out as entry level helpdesk, moved up to desktop support, then a field tech, then systems admin, and now I am a network engineer. I have never used a dmm for my job. Generally speaking, it isn't worth the time to figure out why the power supply isn't working, or why the mobo is having issues. Just replace them.And I will parrot some of the other replies as well. If you get a dmm, just don't use the current measurements. Keep your probes connected to the voltage/resistance inputs and leave measuring current alone.

author: radiolistener
author_rank: Super Contributor
timestamp: June 27, 2023, 06:48:56 am
content: Quote from: cikain on June 24, 2023, 03:11:23 pmNo, for battery powered device (which doesn't have galvanic connection with mains) there is no difference between phase and neutral. But note that GND probe may be connected to a metal case (if any) and if you put GND to phase line it will be very dangerous to touch metal parts of the device.Quote from: cikain on June 24, 2023, 03:11:23 pmNo, for a usual DMM it should show minus sign before measured value. But note that if you're using custom device as DMM it may not support reverse polarity, so you're needs to check it in manual.

author: wasedadoc
author_rank: Super Contributor
timestamp: June 27, 2023, 04:24:53 pm
content: Quote from: EEVblog on June 27, 2023, 01:27:02 am"Anymultimeter" includes analogue multimeters (yes they still exist!). While it might be safe to connect the probes "back to front" it will be rather difficult to get a meaningful measure of voltages and currents!

author: BillyO
author_rank: Super Contributor
timestamp: June 27, 2023, 05:06:41 pm
content: Quote from: wasedadoc on June 27, 2023, 04:24:53 pmThe good ones had polarity switches on them. Junk is junk not matter what decade it was built in.