Repairing vintage ribbon cable

[RobS]

Recently a former Honeywell field engineer gave me this ten foot long 36 way ribbon cable made in 1965 to use on my Honeywell 200 replica project but four of the 36 conductors are open circuit.



There are three ribbons each holding twelve black conductors embedded in the plastic ribbon.



The ends of the conductors appear to be soldered onto the tracks on the connector boards.



I measured the resistance of one of the conductors and got a reading of 0.7 Ohms for the ten foot run. From what I can find out on the internet these could well be carbon ribbons with graphite conductors in them although I also read that some contain metal tapes. My question is how I can repair the faulty conductors. I can probably trace the location of the faults by pricking through the plastic tape with a needle to attach a meter if the faults aren't in the soldered end connections but can such a ribbon be cut and rejoined?

Has anyone had any experience with this type of ribbon, especially one so old?

 

[Caleb H]

Looks pretty similar to a flex PCB. I've made flex PCBs at JLCPCB, and I've also repaired them using conductive paint pens.

 

[daver2]

That would be my first thought also - conductive silver paint.

You will have to find out where the break is (pins are the obvious weapon of choice), then scrape away the insulation from either side of the break, apply the conductive paint, cross your fingers and (if it works) find some way of insulating the resultant 'fix'.

Dave

 

[RobS]

Thanks for that suggestion chaps but I'm still wondering about those soldered connections at the ends of the ribbons. There are clearly what appear to be metal tags soldered to the PCBs. Would they have been embedded in the plastic just at the ends during manufacture? If so that means that some other method of connecting the ends to PCBs would be needed if I shortened a ribbon. I suppose that some means of gripping the ribbon without solder being used would work. Even so cutting the plastic ribbon to the right depth will be tricky as there are no signs of it being laminated along the edges so it cannot just be split apart.

I was surprised to encounter a ribbon cable from that era as I haven't seen any other signs of it having been used in Honeywell 200 computers back then. All the other H200 cable connectors that I have seen have had separate wires laced together into cable harnesses attached to them.

 

[syzygy]

There are clearly what appear to be metal tags soldered to the PCBs. Would they have been embedded in the plastic just at the ends during manufacture?

They certainly could have been....something like this...

From https://www.digikey.com/en/products/detail/te-connectivity-amp-connectors/FSP-22A-12/5591822

Looks like some kind of soldering tool was used (maybe during manufacturing) that leaves those two dimples on on the joint to the board. Note that it looks like three connections were re-flowed at some time. If you tried to use the cable without the wire ends you would still have the flat ribbon trace to work with but flexing would be a problem I would think.

I wonder if they start out as 'normal' wire and are flattened into the "trace" during manufacture - I don't know.

Still, if you can keep the length as is, the silver pen, as suggested, would seem to be the way to go.

 

[RobS]

Thanks for the advice chaps.

 

[andy]

If you can make a reliable repair, you may want to just replace the ribbon cables. Ones that use wire all the way through would be idea.

 

[RobS]

Andy: A key aspect of my replica Honeywell 200 project is that I am trying to use original Honeywell components from the 1960's as much as possible, so even acquiring an original H200 ribbon cable with the date 1965 stamped on one of the connector boards came as a surprise and I would prefer to preserve it. If I can't repair the broken conductors then I'll just use the other ones. However, at present while I am designing and building the computer there are likely to be two backplanes that are temporarily ten feet apart that will need such a cable across the room between them but once the component parts are all together in a cabinet (in the distant future) nothing in the machine will need ten feet of cable to connect it up.