Help repairing Cut ribbon cable - Page 1
Forum section: electronics / repair

author: OmegaHyperion
author_rank: Contributor
timestamp: August 16, 2017, 10:51:51 am
content: Hello all,So, to make a long story short, i have a piece of equipment that was not removed properly from its original home. This resulted in the cutting of, among other things, a ribbon cable.The cable is a rather coarse one if i recall, with around 20 conductors. The cut is clean and more or less square to the cable.So, since i want to get this piece of equipment working once more, i need to mend this cable. (or replace it)So, since i have never had to deal with a cut ribbon cable before, i decided to ask you guys for help.Note: The cable is not flat flex, its individual strands of copper coated in insulation and molded together with the conductor next to it.So, here are the options i have come up with sofar:- Replace the cable completely (more time consuming, as it is not a standard cable)- Solder together each conductor and put heat shrink on top- Get crimp cable connectors to reconnect the cableSo, which should i go for?If anyone has another idea, please tell me

author: bd139
author_rank: Super Contributor
timestamp: August 16, 2017, 11:09:00 am
content: If it's IDC connectors at each end, replace the cable. You can usually get it in short lengths from a supplier and the connectors individually. The connectors can be put on with a standard vice if you don't have the correct tools.If there is enough length left in it to do this, you can cut it either side of the break and put an IDC connector on each end and then use double pin headers to connect the two halves together. This is ugly but it works quite well.I'll probably get shot as there are proper tools for this, but I cut it with a pair of large sewing scissors against an engineers square.

author: floobydust
author_rank: Super Contributor
timestamp: August 16, 2017, 06:09:43 pm
content: I'd make a new one. I use a bench vise with wood blocks to crimp IDC connectors and it's DIY... Just make sure you know if it has a twist or flipped connector on one end.Digi-key will "value add" and premake a ribbon cable with certain ends/lenght.

author: KL27x
author_rank: Super Contributor
timestamp: August 17, 2017, 02:46:18 am
content: QuoteQuoteSounds like you could mend it in less than an hour, but if it's a very high speed signal, with redundant ground wires between each signal, it might lose some signal-to-noise and increase in EMI to surrounding cables. But 'twere me, I'd just mend it and see what happens. If the gauge is regular, say 0.05" pitch, you could use a piece of double-sided vero board to make the splice. Then wrap it over with electrical tape.

author: OmegaHyperion
author_rank: Contributor
timestamp: August 17, 2017, 02:39:03 pm
content: Thanks for the responses so far.I should probably clarify as to what signals are run threw the cable. To my knowledge, its DC power (various voltages) as well as analog signals. (sub 10MHz if im not mistaken).Maximum voltage is 400V DC. Other then the voltages, there are 4 analog data lines, which drive a CRT unit.

author: cdev
author_rank: Super Contributor
timestamp: August 17, 2017, 05:01:06 pm
content: Just be safe- 400v is a high voltage to be making assumptions about what you think you need to do. Try to get as much info as you can about this specific repair.Individual wires coated in rubber implies potentially dangerous high voltages to me.

author: floobydust
author_rank: Super Contributor
timestamp: August 17, 2017, 05:22:43 pm
content: OmegaHyperion, post a pic. It will help us give better advice.

author: OmegaHyperion
author_rank: Contributor
timestamp: August 17, 2017, 10:31:12 pm
content: Here is the best picture of the cable i could come up with on the spot. Its a crop from a larger image, where the cable is visible.I wont be able to go to the machine until Monday at the soonest, so this will have to do for now.I have some working experience with "High Voltage", though i don't consider 400V particularly high, nor is it the highest voltage in this machine. That would be 10KV (CRT acceleration voltage), i need to fix the cable as well, but i think i figured out how to mend it. By creating a nylon cylinder with inner space for epoxy resin, that goes about 2 or 3 cm over the cables. covering the solder joint, in addition to heat shrink covering the epoxy sealed cylinder.As to the voltages i have worked with, i have worked with up to 50KV AC and close to 100 KV DC. (though never inside of equipment, it was mostly in a lab environment, with a very long non conducting stick (not wood, for obvious reasons)The cable in question connects one of the CRT's of this machine to its video amp board. Im guessing here (as i have yet to look over the schematics for the CRT its self) the 400V is for the electron gun of the CRT. (the voltage is indicated on the video amp schematic where the connector goes to)

author: helius
author_rank: Super Contributor
timestamp: August 17, 2017, 11:09:00 pm
content: That's right, 400V would be for the screen grid (G2). As a temporary matter PVC electrical tape should be sufficiently insulating, but your solution of an epoxy bond covered in heatshrink would be a better permanent fix.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: August 17, 2017, 11:44:42 pm
content: That is not much of a photo. Try with higher resolution.

author: VK5RC
author_rank: Unknown
timestamp: August 18, 2017, 12:22:27 am
content: Not sure if this technique will work with that cable type (hard to tell from the photo) and possibly 400v. I would think of its own new wire if you can identify which wire has the high voltage. I generally don't 'bodge' high voltage!https://www.eevblog.com/forum/testgear/restoring-display-flex-on-an-old-micronta-22-191/Regards Rob

author: OmegaHyperion
author_rank: Contributor
timestamp: August 19, 2017, 06:36:52 pm
content: I managed to find the other end of the cable (its long, and in a large machine), and its connected to a proprietary connector. However, i should be able to (and am forced to) replace the entire cable, reusing the original connectors.Its a standard 14 conductor ribbon cable. If anyone wants to see the cable its self, ill upload the images.The high voltage (10KV) cable will need to be done with the nylon epoxy method i described earlier, as one end has the CRT cap, and the other a high voltage supply on it.There are other cables that need replacing as well. These are also standard ribbon cables, but i will probably replace some of them with round multi core cable, allowing me to add a nylon sleeve. (to protect against wear, as some of them had damage to the insulation)Thank you everyone for your help