Testing a usb2/usb3 cable using a multimeter

[fig]

Hello could you please help.
I have a multimeter but don't know how to use it properly. The sort of answers I'm looking for when searching google are.
1- does the cable have a partial break in it.
2- is the cable fit for what I'm using it for.

To be clear e.g. a usb cable has four wires in it and each wire is made up of many thin wires, what if the majority of those thin wires were broken and only a few remained intact what (bad things) would happen and how do I test for that. Also how can I test a cable to determine if it's usb2 or usb3.
Thanks

[fruit-uk]

Hello could you please help.
I have a multimeter but don't know how to use it properly. The sort of answers I'm looking for when searching google are.
1- does the cable have a partial break in it.

Easiest way is to grab an old cable with a matching plug/socket and chop it in half.
Strip sheathing and cables to leave enough bare end as a contact. Do this for both ends then use continuity on your meter to check black-black, red-red etc.

2- is the cable fit for what I'm using it for.

If you mean USB 2 or 3, look at the plug on the end!

There are other things to consider too eg. is your cable nearly all plastic with very little wire inside - as seems to happen too often!

[RST8]

Hello could you please help.
I have a multimeter but don't know how to use it properly. The sort of answers I'm looking for when searching google are.
1- does the cable have a partial break in it.
2- is the cable fit for what I'm using it for.

To be clear e.g. a usb cable has four wires in it and each wire is made up of many thin wires, what if the majority of those thin wires were broken and only a few remained intact what (bad things) would happen and how do I test for that. Also how can I test a cable to determine if it's usb2 or usb3.
Thanks

The short answer is if you have reason to suspect the cable is broken, throw it away, it just isn't worth the time to fix it or diagnose issues and if the majority of wires are broken, you are going to have issues.
If you really want to persist, then your multimeter should have a resistance tester, set it to the lowest scale, in the hundreds of ohms, test each connection using the probes, the reading should be fairly close to zero ohms resistance for each end, with no reading between each of the adjacent connectors.

If you do a quick google on USB 2 vs 3 cables, you'll see there is a difference.
You don't mention what you are using it for, but if your data needs really require USB 3, buy a decent cable, it's just not worth the bother using cheap or damaged ones.

Joe

[fig]

Thanks for the replies but I'm asking about how to use a multimeter to test a cable(usb in this case). Words like impedance, resistance and ohms are mentioned in articles but not explained in layman's terms.

Easiest way is to grab an old cable with a matching plug/socket and chop it in half.
Strip sheathing and cables to leave enough bare end as a contact. Do this for both ends then use continuity on your meter to check black-black, red-red etc.

There would still be continuity if the cable was partially broken but is there any way to test for a partial break using a multimeter.

The short answer is if you have reason to suspect the cable is broken, throw it away, it just isn't worth the time to fix it or diagnose issues and if the majority of wires are broken, you are going to have issues.

Is it possible to test for those issues using a multimeter.

[BMS Doug]

You are looking for a break in the wires, this will be indicated by a lack of continuity or a high resistance.

Resistance is measured in Ohms and is symbolised by the greek letter Omega


On this cheap multimeter (below) there are a selection of settings for resistance, you would want to set the multimeter to the lowest of these scales (200 in this case). The meter will then read a resistance value between 0- 200 Ohms).


With the leads not connected to anything you will have a high off-scale reading (you would also expect to see this if a wire was completely broken).

With the leads shorted to each other you will probably see about 0.2 Ohms (this is the resistance of your test leads and should be subtracted from any tests you do), if this reads 0 then your multi-meter is not capable of resolving the level of detail needed to show truly low resistance values.

To test a cable you will need to connect the multi-meter to each end of the cable at the same time, the easiest way to do this was described by fruit-uk.

check the resistance of each wire in the cable in turn, they should each be very vow.

don't check resistance while voltage is present, your multi-meter wont like it.

[RST8]

The short answer is if you have reason to suspect the cable is broken, throw it away, it just isn't worth the time to fix it or diagnose issues and if the majority of wires are broken, you are going to have issues.

Is it possible to test for those issues using a multimeter.[/quote]

Not really. A multimeter will tell you if there is break in the cable, or a short, but it is measuring this using DC current, not transmitting data. A USB cable will be sending signals at very high frequency and whilst the multimeter might show minimal resistance, no breaks or shorts with DC current, this doesn't mean that it will work when carrying USB data. A cable will act very differently when transmitting data at high frequency, the higher the transmission rate, the more demands made on the cable, which is why there are different form factors and standards and why there are limits in the lengths a cable can be.

To really test your cable, you will need a dedicated cable tester, such as
http://www.amazon.co.uk/Andoer-Remote-N ... ble+tester

But again I would suggest just buying a new cable, it's really not worth investing any time in the problem.

Joe

[drgeoff]

Breaks in cables are often intermittent. By flexing the cable in the right place, usually (but not always) at or close to where the cable goes into the plug moulding, the resistance will change. An old fashioned analogue meter is much better for seeing that.

Getting meter probes to touch the contacts in the plugs is fiddly and troublesome. As others have said, get another cable. If things work with the new one but not the old one then the old one was faulty and should be cut up and discarded. If the new cable doesn't work your problem is elsewhere.

[fruit-uk]

If things work with the new one but not the old one then the old one was faulty and should be cut up and discarded.

Or cut up and used for future use or tests - they come in very handy at times.