Ideas on finding a break in a length of multicore cable?

Thread Starter

seanstevens

Joined Sep 22, 2009
121
Hello all,

Looking for ideas, I have a PlayStation VR that has stopped working, I know the reason is 2 wires seem to have disconnected/cut somewhere in the length of the multicore (~30 wires) shielded cable. I know the 2 wires are cut most likely due to pressure or stretch somewhere in the 2 1/2 meter or so length of the cable, as I have continuity tested all the connections from one end of the HDMI connector to the inside of the VR headset connector.

I have looked at the condition of the cable, it doesn’t look too bad, a couple of small stressed/bend areas about 10mm, spliced the cover and found nothing broken there.

So, I don’t want to be splicing the whole cable in a random fashion or cut it in half and test each half, I am trying to keep the splicing to a minimum.

Would a TDR work in such a short distance?

I have already tried a 40dB EMI/EMC amp with its small loop antennas used in radiated EMC detection, it shows a lot of radiated stuff when moved over the cable cover with the unit switched on, but I was hoping to see an obvious drop in signal somewhere on the cable, but no luck it all looks the same, it was a long shot.

Thanks
 

AlbertHall

Joined Jun 4, 2014
12,023
I have already tried a 40dB EMI/EMC amp with its small loop antennas used in radiated EMC detection, it shows a lot of radiated stuff when moved over the cable cover with the unit switched on, but I was hoping to see an obvious drop in signal somewhere on the cable, but no luck it all looks the same, it was a long shot.
Maybe, ground all the other wires and connect a signal generator to the fault wire and then go hunting with the loop?
 

Thread Starter

seanstevens

Joined Sep 22, 2009
121
Maybe, ground all the other wires and connect a signal generator to the fault wire and then go hunting with the loop?
One end is HDMI, easy enough, the other end is tiny tiny connector that I had to use needle probes for the continuity test. I suppose I could feed something in on the HDMI side and try to trace it. Still not easy though. But still its a good idea!
 

MisterBill2

Joined Jan 23, 2018
11,900
A method that I have used for locating breaks in long power cords is to apply a high voltage to the ends of the wire with the break, and then see where the resulting arc burns through the insulation. This should only be done outside, and away from combustibles. And note that it does damage a small section of the cable.

OR, feed a signal into one end of the broken wire and ground the other end and then us a capacitive pickup along the cable to detect the change in amplitude. Since it is a shielded cable, the shield and all other wires should also be grounded. The picked up signal will be very weak.

But it may be better to recycle that cable and waste money on a replacement, because HDMI is a junk scheme anyway. It is the poor quality cheaper replacement for DVI connectors.
 

Thread Starter

seanstevens

Joined Sep 22, 2009
121
A method that I have used for locating breaks in long power cords is to apply a high voltage to the ends of the wire with the break, and then see where the resulting arc burns through the insulation. This should only be done outside, and away from combustibles. And note that it does damage a small section of the cable.

OR, feed a signal into one end of the broken wire and ground the other end and then us a capacitive pickup along the cable to detect the change in amplitude. Since it is a shielded cable, the shield and all other wires should also be grounded. The picked up signal will be very weak.

But it may be better to recycle that cable and waste money on a replacement, because HDMI is a junk scheme anyway. It is the poor quality cheaper replacement for DVI connectors.
Thank you for the suggestions. I think I was reading about your method of high-voltage here when I was searching, either posted by you or someone else suggested it. I think that method is a little too damaging to the many neighbouring tiny wires and may cause more problems than it may solve However the capacitive method is good, I will look into trying that.
 

Thread Starter

seanstevens

Joined Sep 22, 2009
121
Measuring the capacitance between the faulty wire and another wire from both ends should give the ratio of the lengths from each end to the break.
Thank you, sounds like a good method, I haven't got a capacitance meter, I do have a scope, is that any use?
 

Thread Starter

seanstevens

Joined Sep 22, 2009
121
But it may be better to recycle that cable and waste money on a replacement, because HDMI is a junk scheme anyway. It is the poor quality cheaper replacement for DVI connectors.
Sony refuses to sell the cable on its own. It is not just an HDMI cable, its a multicore cable with a 40 odd tiny SMD connecter at one end and on the other end an HDMI and a sony propriety connecter terminate the cable, so no way of making up a cable.
I agree with your assessment of HDMI, still better than the massive SCART disaster connector!
 

MisterBill2

Joined Jan 23, 2018
11,900
Another scheme, used for coaxial cables and data lines, is pulse reflection time measurement. That uses a scope and a fast pulse to measure the time for the pulse to be reflected from an impedance discontinuity. The pulse is created by a line-driver IC and so it is not a complex scheme. That can give you the proportion of the distance relative to the length of the whole cable length.

And it is worthwhile to know about the Sony repair parts policy.
It puts Sony products on my "Do not ever buy" list.

The high voltage method works very well for heavier extension cords, where the break is usually at an end, at least they have been for me. So I have 98 foot cords and 49 foot cords.
 

Ya’akov

Joined Jan 27, 2019
5,666
The method that @MisterBill2 is suggesting is usually called Time Domain Reflectometry (TDR) and it can be reasonably accurate though the shorter the cable the less reliable since the return time is shorter.

One possibility that uses a higher voltage is to apply an AC voltage (24VAC would probably do it), live and neutral, to two of the wires in the cable with no termination and ensure there no short at the end then use an ordinary but decent quality NCV (Non-Contact Voltage) detector like this Klein NCVT3P to follow the voltage up the cable until the indication stops. This works surprisingly well. I recommend the Klein because it has the low voltage range and is a known good device but you could use a cheaper one with 120VAC if you wanted to go that way, just be very careful.

1651055474926.jpeg
 

MisterBill2

Joined Jan 23, 2018
11,900
The method that @MisterBill2 is suggesting is usually called Time Domain Reflectometry (TDR) and it can be reasonably accurate though the shorter the cable the less reliable since the return time is shorter.

One possibility that uses a higher voltage is to apply an AC voltage (24VAC would probably do it), live and neutral, to two of the wires in the cable with no termination and ensure there no short at the end then use an ordinary but decent quality NCV (Non-Contact Voltage) detector like this Klein NCVT3P to follow the voltage up the cable until the indication stops. This works surprisingly well. I recommend the Klein because it has the low voltage range and is a known good device but you could use a cheaper one with 120VAC if you wanted to go that way, just be very careful.

Not sure how well that would work, because this is a shielded cable. This method, described in post #10, is similar to what I suggested previously, except that I suggested using an audio signal and a listening amplifier. A similar concept but a different technology.
 

Ramussons

Joined May 3, 2013
1,264
The method that @MisterBill2 is suggesting is usually called Time Domain Reflectometry (TDR) and it can be reasonably accurate though the shorter the cable the less reliable since the return time is shorter.

One possibility that uses a higher voltage is to apply an AC voltage (24VAC would probably do it), live and neutral, to two of the wires in the cable with no termination and ensure there no short at the end then use an ordinary but decent quality NCV (Non-Contact Voltage) detector like this Klein NCVT3P to follow the voltage up the cable until the indication stops. This works surprisingly well. I recommend the Klein because it has the low voltage range and is a known good device but you could use a cheaper one with 120VAC if you wanted to go that way, just be very careful.

That would mean a TDR with a pulse width less than 10 nSec !!! Much cheaper to buy a new cable :D
 

Thread Starter

seanstevens

Joined Sep 22, 2009
121
@MisterBill2, Thank you, I did wonder about the usage of TDR in my original post, but as the cable is fairly short, I didn't think it was an easy way - from my original post "Would a TDR work in such a short distance?"
And yes, sony is now on my list too!
@Yaakov, thank you, another good idea, but I probably will try @AlberHall and send some signal down from the HDMI connector and try to trace it to the break.

Thank you all for all the good ideas.
 
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