Can Multimeter Detect Inconsistencies in Wiggle-Test? - Page 1
Forum section: electronics / beginners

author: Boris_yo
author_rank: Frequent Contributor
timestamp: July 07, 2022, 06:04:43 am
content: Hello. Based on what I have observed, I suspect 24-pin motherboard connector on my desktop computer to have faulty wire/wires. Can cheap multimeter detect inconsistencies in power supply when testing one wire at a time by wiggling-testing?I have cheap PSU tester but I doubt it would be sensitive enough to pick voltage inconsistencies. The problem is in one of power supplying wires while others work properly I assume PSU tester won't detect anything.I don't necessary need to figure out exactly which wire/wires are failing. Know that one of essential wires is failing is good enough to disqualify 24-pin connector as faulty and replace it.

author: theHWcave
author_rank: Regular Contributor
timestamp: July 07, 2022, 06:59:24 am
content: Well, you could use continuity mode of the multi-meter to check each ground pin of the connector against chassis ground (or against one of the other ground pins) while wiggling the black wire in question. Then you could use a piece of wire to connect the green PS-ON to ground which should turn the power on. Measuring one of the power voltages for drops while wiggling the green cable would show whether the green wire has a problem. If not, you could then proceed to measure each of the voltages at the connector while wiggling the corresponding wire to check for dips. Alternatively, just replace the whole cable+ connector. Another check is to use contact cleaner into the connector and inserting it a few times to see if the problem was actually bad contact of the connector rather than the cable. Lastly, examine the soldering of the receptacle on the PCB to see if the problem is actually a bad solder joint.Some PSUs may need to see load to produce voltage. So, consider a power resistor in parallel to your voltmeter to draw some current.

author: Boris_yo
author_rank: Frequent Contributor
timestamp: July 07, 2022, 09:26:19 am
content: Quote from: theHWcave on July 07, 2022, 06:59:24 amThe first method of testing continuity will allow me to find out if wires have physical damage inside, while the second method will allow me to detect voltage interruptions that go outside of proper range set for motherboard? I have done the latter test with power supply working and the voltages were within the proper range. I will try doing both methods again but this time with wiggle-test.Can there be a situation where I won't see any physical faults with first method while wiggle-testing but will see voltage interruptions with second method?My power supply is not fully-modular and replacing 24-pin connector would mean replacing entire power supply

author: Stray Electron
author_rank: Super Contributor
timestamp: July 07, 2022, 02:16:33 pm
content: Yes, some multimeters can usually catch those but but digital MMs update too slow to display them. You might see some flicker and random numbers on the display but they will be meaningless. Use the continuity buzzer (if it will withstand the voltage that you are measuring) on your DVM orbetter yet use an analog meter.

author: ebastler
author_rank: Super Contributor
timestamp: July 07, 2022, 05:31:41 pm
content: If you want to use the continuity buzzer, first make sure it has a fast enough response -- it can respond rather slowly in some cheap multimeters:Set your meter to "beep" mode, take one of the probes in each hand, and flick them against each other very briefly (like if you were fencing). You should hear brief clicks from the buzzer.If the buzzer responds too slowly and remains silent, then it will likewise not be able to detect brief interruptions when you measure and wiggle your cables under test.Edit: Oh, and donotconnect an external voltage while doing your continuity measurements! (I.e. switch the computer off.)

author: Gyro
author_rank: Super Contributor
timestamp: July 07, 2022, 05:43:04 pm
content: This is a case where the better quality meter continuity buzzers (the latching ones) can work against you. Extending the tone from a fleeting contact acts against you when you are looking for a fleeting interruption. Fast but non-latching is helpful here.

author: rsjsouza
author_rank: Super Contributor
timestamp: July 07, 2022, 05:58:07 pm
content: One additional aspect: if in your wiggle tests you find no issues at all with the cables, you can suspect the connector itself. The DMM will not catch that, unless you test the continuity between the connector and the motherboard header (the pads in the bottom layer).I have seen issues on this interface that caused intermittent problems on motherboards - when there was a strong current draw, a loose spring contact blade gave up and caused a voltage sag.Good luck in your investigation!

author: Shock
author_rank: Super Contributor
timestamp: July 08, 2022, 03:03:58 am
content: Most issues can be resolved either cleaning, resoldering or retensioning the connector. If the device has been sitting years it's normally oxidized contacts.

author: tooki
author_rank: Super Contributor
timestamp: July 08, 2022, 03:12:38 pm
content: Quote from: Gyro on July 07, 2022, 05:43:04 pmNot necessarily: some Fluke meters (like the 12 and 16) can also be set to capture “short to open” continuity (in addition to the usual “open to short” continuity). Others, like my 87V, claim to detect both short and open intermittent continuity. From the 87V manual:QuoteI interpret this to mean that it will latch on an intermittent open, too, extending the gap in the beep, making it easier to hear.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: July 08, 2022, 05:48:43 pm
content: Any DMM with a Min/Max function can pick up blips in voltage, and beep when doing it.Easy-Peasy.

author: wizard69
author_rank: Super Contributor
timestamp: July 10, 2022, 01:09:57 am
content: I recently had a similar problem with a robot and its I/O board. I actually narrowed the problem down accidentally when my forearm rubbed up against a bundle of wires. This lead to finding the faulty connector area. I then just replaced all the pins on the wire to board connector and also resoldered the pins on the circuit board jack.Now this might seem to be excessive but being absolutely sure the the potential one wire was not possible. Better to make everything 100% and not have to return to the problem. By the way the connector we are talking about here is of the same family as PC power supply connectors, the pins and sockets do loosen up over time. Thus there are two really high things on the possibilities list, that would be bad solder joints and the second being Loose sockets.

author: Boris_yo
author_rank: Frequent Contributor
timestamp: July 19, 2022, 10:57:05 am
content: Quote from: theHWcave on July 07, 2022, 06:59:24 amI am not sure I understand the part where I should wiggle the green cable. I used a small wire to connect pin #16 PS-ON with pin #17 Ground to start the power supply. I did not use resistor because I don't have it and I am also not experienced enough in working with resistors.I have tested continuity with all Ground pins and cointinuity with live pins with power supply off. Tried wiggling but have not noticed interference. Later I connected 3 chassis fans to power supply when testing voltage output. The voltages were stable until I pushed down and/or wiggled a group of cables residing on 4-pin connector. I think cable that connects to pin #12 causes voltage drops. It was hard to determine if there are other cables that cause it as well.I don't know if it is worth it to deal with international RMA because entire power supply will need to be replaced due to it being semi-modular. As long as cables on 4-pin connector are not being touched I probably should not worry and deduct motherboard cable from troubleshooting? Maybe I should buy contact cleaner either way and clean pins?Quote from: Stray Electronebastler told me to use continuity without powering on power supply. It is what I did.Quote from: rsjsouzaI have performed continuity tests without powering on power supply. I have not noticed any changes. Maybe I have not wiggled hard enough because I was afraid to cause damage? But then, during testing with power supply being powered on I have noticed that there is a voltage drop when wiggling all 4 cables in 4-pin connector (G, +12v, +12v, +5v). Specifically I feel that wiggling the cable connected to pin 12 causes voltage a drop. It shortly returns to normal readings even if I keep wires pushed down/wiggled. But since the motherboard cable is supplying a consistent voltages I probably should not be worried about interference. At least I can deduct it from motherboard troubleshooting.What is this loose spring contact blade on a motherboard that you mentioned by the way?Quote from: ShockThe computer has been purchased 2 years ago. I don't have electronic contacts cleaner at home. If retensioning requires a special tool then I don't have it. I have Isopropyl alcohol 99% though if it can help. Otherwise I will buy the necessary items if you advise so.Quote from: wizard69I feel that I have found the cable that causes voltage drops but it only happens when pushed down and/or wiggled. Strange that it is connected to pin #12 but causes voltage drop in pin #11. I thought these pins are isolated.Do pins and sockets loosen up with time by themselves? I found this 90 degree connector for motherboard connector. It probably would make it easier to plug and unplug motherboard cable and make for a bit more space inside computer chassis. Currently mine noticeably protrudes forth and pointed back 180 degrees in order to connect to the motherboard.